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Maintaining continuity of nutrient intake after weaning. II. Review of post-weaning strategies

Maintaining continuity of nutrient intake after weaning. II. Review of post-weaning strategies Maintaining continuity of nutrient intake after weaning. II. Review of post-weaning strategies †,1 † † † Madie R. Wensley, Mike D. Tokach, Jason C. Woodworth, Robert D. Goodband, ‡ † || Jordan T. Gebhardt, Joel M. DeRouchey, and Denny McKilligan Department of Animal Sciences and Industry, College of Agriculture, Manhattan, KS 66506-0201, USA; Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, || Manhattan, KS 66506-0201, USA; and TechMix Inc., Stewart, MN 55385, USA ABSTRACT:  Low feed consumption during the aggression in heavy pigs. Furthermore, water en- first 3 d post-weaning disrupts nutrient intake and richment with nutrient dense products have been results in what is commonly known as a post-wean- shown to improve growth performance and reduce ing growth check. While most pigs recover from morbidity and mortality in the early post-weaning this initial reduction in feed intake (FI), some pigs period. Because young pigs are sensitive to palat- fail to successfully make this transition leading to ability, diet form and complexity should also be morbidity and mortality. In this review, our ob- considered. Weanling pigs prefer diets manufac- jective is to describe the different post-weaning tured with coarse ground corn (700  μm) com- strategies that can be used to minimize nutrient pared to fine ground corn. Additionally, weanling intake disruption and improve FI in the imme- pigs are more attracted to large diameter pellets diate post-weaning period. Providing weanling (12  mm) compared with small pellets. Despite pigs with an environment that encourages them to these preferences, impacts on growth are relatively search out and consume feed is important. This small. Feeding complex diets with high levels of includes appropriate barn temperatures, resource lactose, animal protein products, or other palat- availability, and nursery placement strategies. able ingredients is another strategy shown to im- Research is needed to better understand the ideal prove growth performance during the first week environmental temperatures to encourage pen ex- post-weaning; however, the initial benefits quickly ploration and reduce time to initial FI. Likewise, diminished as pigs become older. Other strategies mat and gruel feeding are commonly practiced that warrant further investigation include the ef- throughout the industry to increase feed accessi- fect of crumble diets on feed preference and the bility; however, limited research data is available to concept of perinatal or social interaction flavor validate protocols or benefits. Nursery placement learning. In summary, strategic post-weaning nu- strategies include sorting light weight pigs into trition and management practices must focus on uniform body weight groups and average or heavy maintaining continuity of nutrient intake in order weight pigs into variable body weight groups to to reduce morbidity and mortality in the imme- provide benefit to light pigs while reducing initial diate post-weaning period. Key words: feed intake, nutrient disruption, pig, post-weaning © The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. This is an Open Access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Transl. Anim. Sci. 2021.5:1-16 doi: 10.1093/tas/txab022 Corresponding author: wensleym@ksu.edu Received November 20, 2020. Accepted February 2, 2021. 1 Wensley et al. INTRODUCTION for FI after weaning. Factors that have a significant impact on post-weaning behavior and consequently In modern swine production, weaning often oc- FI, include barn temperatures, agonistic behavior curs during a critical window of gut maturation, or hierarchy establishment, lack of feeding stimuli, marked by increased epithelial function, microbiota feed palatability, and resource availability (Brooks colonization, immune cell proliferation, and enteric and Tsourgiannis, 2003), many of which will be nervous system development (Moeser et al., 2017). covered herein. Furthermore, the transition from Excessive immune stimuli in response to weaning a single milk-based diet (sow’s milk) to separate stressors during this period has been linked to im- feed and water sources, requires an abrupt learn- paired neurodevelopment (Kelly et  al., 2015) and ing period that pigs must adapt to after weaning gastrointestinal (GI) maturation (Moeser, 2016; in order to familiarize themselves with the differ- Pluske, 2016). Williams et  al (1997) also reported ence between hunger and thirst satiety (Brooks and a reduction in feed intake (FI), low protein accre- Tsourgiannis, 2003). It is for this reason that water tion, and diminishing body leanness as a result of consumption remains elevated for the first several chronic immune system activation. Inflammatory days post-weaning (Brooks et al., 1984). However, cytokines which are released in response to immune once feed is discovered and pigs become more com- stimuli are known to further suppress appetite and fortable in their new environment, normal eating inhibit nutrient absorption (Escobar et  al., 2004). and drinking patterns are established (Brooks et al., In herds under chronic disease challenge, prolonged 1984). production of cytokines induces muscle and fat ca- The question then becomes how we can increase tabolism, as well as impaired carbohydrate metab- exploratory behavior and encourage FI early after olism (Matthys and Billiau, 1997; Escobar et  al., weaning. In an attempt to investigate the social 2004). This deterioration in energy metabolism learning behavior of piglets after weaning, Morgan can be detrimental to the central nervous system, et  al (2001) observed that experienced eaters were altering the brains ability to function properly able to stimulate earlier feeding behavior in wean- and elicit physical responses to stimuli, including ling pigs who were unfamiliar with solid feed. When the newly weaned pigs’ decision to search out and housed in the same pen as experienced eaters, inex- consume feed. perienced eaters exhibited increased FI and more Low FI after weaning reduces the flow of nutri- frequent visits to the feeder, compared to pens that ents through the GI track, resulting in what is com- housed only inexperienced eaters. These results in- monly known as a post-weaning growth check. This dicate a potential mechanism where eating behavior period is marked by body weight (BW) loss and in- and exploration is learned by non-eaters from those testinal disturbances that lead to a high occurrence already consuming feed. Pairing inexperienced of GI inflammation (McCracken et  al., 1999) and eaters with those familiar with solid feed may also diarrhea. While most pigs recover from the initial encourage the pigs innate drive for synchronized reduction in FI, some pigs fail to successfully make feeding like suckling; however, this has not been this transition leading to morbidity and mortality. fully proven. Interestingly, recent data suggests that The objective of this review is to describe the dif- the day of weaning may not be the best time for pigs ferent post-weaning strategies to minimize nutrient to discovery solid feed, due to the stress of weaning intake disruption and improve FI in the immediate on the pigs learning ability (Millet et al., 2019). The post-weaning period. authors investigated the effect of allowing newly weaned pigs an opportunity to rest (18 h) and get acclimated with their new environment before feed Post-weaning FI was provided in the pen. Pigs that received feed 18 h The primary limiting factor affecting FI in newly after weaning had increased FI and average daily weaned pigs is their physical capacity to ingest feed gain (ADG) from d 0 to 21 compared to pigs that (Li and Patience, 2017). Therefore, low FI immedi- received feed at weaning. This feed management ately post-weaning often does not provide enough strategy could offer a way to synchronize pigs to eat nutrients to the pig to satisfy maintenance require- together, stimulating pigs to search out feed when ments, subsequently leading to reduced growth. they hear it dropped into feeders. This concept re- However, it is important to understand what fac- quires more research. Nonetheless, it is apparent tors are involved in the regulation of FI in newly that behavior plays a crucial role in initial FI. weaned pigs in order to develop successful manage- While external stressors tend to be additive in ment and feeding programs to better prepare pigs their negative effects (Hyun et  al., 1998), it is well Translate basic science to industry innovation Continuity of nutrient intake after weaning established that increasing nutrient intake after wean-to-finish facilities with large pens sizes, can weaning can minimize stress associated losses in help accomplish a range of temperature zones that intestinal barrier function (Wijtten et  al., 2011; are suitable for pigs of all sizes. When temperatures Verdonk, 2006). Consequently, feed deprivation reach the upper boundary of the thermoneutral (72 h) has been reported to alter the endocrine and zone, pigs will often search out cool, damp places neuroendocrine axis and hypothalamic pituitary to lay, spreading out across the pen in an attempt to adrenal (HPA) axis hormones, negatively influ- avoid contact with other pigs. As a result, pigs will encing FI (Salfen et  al., 2003). Stress conditions, often decrease FI and increase water consumption. such as those surrounding the time of weaning In contrast, when temperatures reach the lower are thought to suppress feed consumption due to boundary of the thermoneutral zone, pigs will the anorectic effects of corticotropin release factor often pile close together and if they have already (CRF, Pelleymounter et al., 2000). As a result, ab- found feed, will increase FI to compensate for en- sence of nutrients to the lumen has been shown to ergy used to maintain body heat (NRC, 1981). This increase active ion transport across the epithelial, may be less of a concern immediately after weaning an indicator of intestinal permeability (Carey et al., because many pigs have not yet identified feed. 1994). Likewise, increased intestinal permeability Thus, temperatures below the thermoneutral zone can reduce nutrient absorption capacity (Moeser may instead prevent weanling pigs from searching et  al., 2017), therefore leading to lower BW gain out feed. For these reasons, it is essential that care- (Pluske et al., 2013). takers provide an adequate thermal environment In summary, there are several external and that encourages weanling pigs to discover feed. internal factors that influence FI after weaning. Resource availability.  Providing weanling pigs Consequently, low FI results in decreased intestinal easy access to resources like feed and water is im- barrier function and villous atrophy, followed by portant. Increasing resource availability includes a a period of BW loss that often takes several days variety of management practices for offering pigs from which to recover (Reviewed by Brooks and feed and water, such as feeder design, wet and dry Tsourgiannis, 2003). Therefore, maintaining a con- feeding systems, mat or gruel feeding, as well as tinuous supply of nutrients post-weaning is crucial drinker access. to minimizing the post-weaning growth check and Pluske and Williams (1996) tested the hypoth- ensure a more successful weaning transition. esis that providing water in addition to feed from a single space, wet/dry feeder would stimulate FI com- pared to a single space, dry or multi-space feeder. POST-WEANING STRATEGIES TO However, the use of wet/dry single space feeders re- INCREASE FI AFTER WEANING duced gain in the first week after weaning. The au- thors observed that pigs had difficulty learning how to manage the wet/dry feeder, often filling the bowl Environmental Factors Influencing Nutrient Intake with excess water. It is important to note that pigs After Weaning per feeder space were not considered in this study. Thermoneutral zone.  Caretaker understanding More recently, it was reported that decreasing the of the thermoneutral zone, or effective tempera- number of pigs per feeder hole decreased time to ture, is important in order to prevent heat or cold feeding. Pens of pigs with 3.75 pigs per feeder hole stress of pigs at the time of weaning. In addition began consuming feed approximately 8  h earlier to room temperature, other environmental factors compared to pens of pigs with 6.25 pigs per feeder impacting effective temperature include heat loss hole (Laskoski et al., 2019). via convection, conduction, and radiation which Mat feeding in addition to standard trough in turn are affected by air movement, floor type, feeding has been reported to reduce morbidity and building insulation (Baker, 2004). Other con- and mortality during the first 3-weeks post-wean- tributing factors to the effective temperature in- ing (Corrigan, 2000; Potter et al., 2010). Similarly, clude air quality and humidity (Lammers et  al., there is evidence that gruel feeding pigs reduces 2007). According to PIC’s wean-to-finish guidelines morbidity compared to pigs offered only dry (2019), the recommended barn temperature for pigs feed (Corrigan, 2000). In a series of experiments, at weaning ranges from 23 to 29 °C depending on Corrigan (2000) observed that both gruel and the use of zone heating. The use of zone-heating mat feeding increased feed disappearance, but such as brooders, heat lamps, and floor mats dur - largely due to increased feed wastage. Potter et al. ing the first weeks post-weaning, particularly in (2010) observed a similar response, with mat-fed Translate basic science to industry innovation Wensley et al. pigs exhibiting poorer feed efficiency, particularly also observed less agonistic behavior in groups of when mat-fed for 7 d as compared to 3 d after pigs that came from the same litter. These data are weaning. However, mat feeding increased eating inconsistent with earlier reports that showed mix- behavior the first day after weaning (Corrigan, ing unfamiliar pigs at weaning actually promotes 2000) and resulted in fewer pig removals during FI and improves growth rate (Pluske and Willams, the nursery period (Potter et al., 2010). Providing 1996). pigs feed in the for m of a gruel increased consump- Another strategy that has been evaluated is tion but reduced eating and drinking behavior at sorting by sow parity. Because gilt progeny often the feeder and drinker. Thus, gruel should not be have poorer lifetime performance compared to used to meet all the feeding requirements. Rather, sow progeny, Craig et  al (2017) hypothesized it is recommended gruel be provided intermit- that segregating gilt and sow progeny at place- tently (3–4 times daily) as to still encourage dry ment would improve the growth and survival of FI. This is to prevent pigs from needing a second both groups. However, this strategy resulted in no transition to get them to the feeder once gruel added benefits. feeding has ended. Generally, gruel is prepared As group size increases, the number of dyadic with equal amounts of water and solid feed; relationships a pig must establish also increases however, the amount of gruel prepared often de- (Turner and Edwards, 2004). This suggests that pends on the number of pigs per pen and should there is more opportunity for aggressive behavior only be enough to last a short period of time to between pigs when attempting to establish social prevent feed spoilage. Depending on the health hierarchy. However, Turner and Edwards (2004) status of pigs receiving gruel feed, intensive care observed no elevation in aggressive tendencies as supplements which are highly palatable and often group size increased above 50 pigs per pen com- aromatic can be added to the gruel to further en- pared with a more conventional group size (10–30 courage FI. Similar to the events surrounding pigs). In an earlier review, Turner et  al. (2003) re- suckling, mat or gruel feeding after weaning may ported that as group size increased, weanling pigs help stimulate group feeding behavior; however, had significant reductions in ADG due to decreased more research is needed to fully understand the FI. It is important to note that group number and implications of mat and gruel feeding strategies. space allowance ranged from 3–120 pigs per pen and 0.186–0.74 m per pig, respectively. These re- sults are consistent with previous findings, in which Sorting Pigs at Nursery Placement reduced oor fl -space allowance reduced pig growth Nursery placement strategies influence pig be- performance during the nursery period (Wolter havior and latency to first FI. While weaning into et  al., 2000a). It has also been suggested that re- variable versus uniform BW groups has shown to source placement may affect feeding behavior, par- have little effects on overall performance, heavy ticularly in large groups. To quantify the effect of weight pigs in uniform groups have lower initial FI feeder location on the performance of weanling than heavy weight pigs in variable weight groups pigs, Wolter et  al. (2000b) evaluated two pen de- (Bruininx et al., 2001). More recently, Faccin et al signs using either five two-sided feeders in a single, (2019) observed increased aggressive behavior and central location or five two sided feeders in multiple delayed FI in pens sorted into all heavy pigs com- locations throughout the pen. The use of multiple pared to pens sorted into light or medium weight feeder locations in a large group pen design did pigs. It is likely that heavy pigs spend more time not increase FI or growth. Additional research is establishing dominance than consuming feed. Sex needed to better characterize the eating behavior of also has a known impact on the behavior and per- pigs in different group sizes and spacing allowances, formance of pigs at placement. Bruininx et  al and how feeder arrangement relative to drinker lo- (2001) observed that gilts had increased FI and cation may affect FI and subsequent performance. gain compared to barrows during the first week In summary, these data suggest that sorting after weaning. Similarly, initial mixing aggression light weight pigs into uniform groups may be bene- tended to decrease when sorting groups of pigs by ficial, while remaining pigs should be randomly gender (Colson et  al., 2006). Furthermore, data placed without sorting by weight to reduce aggres- indicates that pigs weaned into familiar groups sion in the heavy weight pigs. In addition to BW, consume more feed and grow faster the first week sorting by sex or socializing pigs prior to weaning post-weaning than pigs weaned into unfamiliar reduces initial aggression and may also increase FI groups (Turpin et  al., 2017). Hwang et  al. (2016) and immediate post-weaning growth. Translate basic science to industry innovation Continuity of nutrient intake after weaning Water Consumption and Enrichment fill immediately after weaning (Torrey et al., 2008). In a series of experiments, Torrey and Widowski The recommended water requirement for nursery (2004, 2006) and Torrey et  al. (2008) investigated pigs up to 27.2 kg BW is 2.8 L per pig per day (NPB, different drinker types on pig preference, intake 2003), which equates to 2.5–3 L per kg of feed con- and wastage. Nipple drinkers resulted in increased sumed. However, in the first 5 d post-weaning, water water wastage and belly nosing behavior compared consumption is typically not linked to FI or physio- to push-lever bowl drinkers (Torrey and Widowski, logical need but rather weaning influenced consump- 2004; Torrey et  al., 2008). The authors suggest tion patterns (previously discussed; McLeese et  al., that motor patterns involved with ingesting water 1992). Water intake tends to be the greatest in the first from bowl drinkers may mimic suckling stimuli 24  h, suggesting dietary supplements may be more that satisfies nosing motivation; therefore, decreas- beneficial when administered through the water rather ing belly nosing behavior. Furthermore, pigs with than feed (Dybkjær et  al., 2006). Options to enrich bowl drinkers spent more time at the feeder. This the water include acidification (De Busser et al., 2011; is in contrast to a later study that indicated pigs Escuredo et  al., 2016), plasma-based globulin prod- with push-lever bowls spent less time at the feeder ucts, glucose or lactose-based energy products, elec- (Torrey et al., 2008). Despite water usage and time trolytes, or a combination of enrichments (Steidinger spent at the feeder, drinker type did not influence et  al., 2002; Myers et  al., 2011; Morris et  al., 2017; FI or ADG. When given a choice between different Schmitt et al., 2018). Studies have reported improved drinker types, weanling pigs found nipple and growth performance in the early post-weaning period oa fl t bowl drinkers faster than push-lever drinkers when water-soluble sources of animal plasma protein (Torrey and Widowski, 2006). Throughout the dur- and energy are provided in the drinking water, with ation of the study, pigs continued to prefer nipple diminishing results thereafter (Steidinger et al., 2002; and float bowl drinkers over push-lever bowls, Vande Pol et al., 2017). Reductions in morbidity and which may be due to easier water access. Based on mortality have also been observed with water enrich- these three experiments, the authors recommend ment (Morris et al., 2017; Schmitt et al., 2018). While the use of push-lever bowl drinkers to prevent ex- most water enrichment strategies are administered cessive water wastage while not negatively affecting during the first 3 to 7 d post-weaning, timing and dur - FI and BW gain (Torrey et al., 2008). ation of administration may influence efficacy. It is also important to consider the impact of According to the Swine Housing and Equipment water quality, particularly sulfate concentrations Handbook (MWPS, 1983), there should be 10 and total dissolved solids, on water and feed con- nursery pigs per nipple drinker space; however, a sumption. Patience et al. (2004) observed that sul- ratio of 25:1 is more common in the US industry fate levels up to 1,650 mg/L did not hinder growth (Jackson, 2007). Because too few waterers can re- performance. Flohr et  al (2014) observed that duce water intake and consequently FI, Jackson adding sodium sulfate at higher levels (3,000 mg/L) (2007) investigated the effect of increasing water resulted in a significant impact on growth perform- access in pens of 25 pigs. When pigs were offered ance. Conversely, earlier reports suggest that water more places to drink, they visited the water bowl containing high levels of total dissolved solids more frequently. This tended to increase ADG (4,390 mg/L, 2,650 mg of SO /L, 947 mg of Na/L, throughout the nursery period. Interestingly, pigs 288  mg of C/L, 88  mg of Mg/L, 70  mg of Cl/L, demonstrated drinker location preference with the and 15 mg of K/L) may actually promote water and alley waterer receiving the fewest visits compared to FI during the first 10 d post-weaning (Maenz et al., waterers located on the same side of the pen as the 1994). High levels of sulfate and dissolved solids feeder or on the back wall. Furthermore, Turner may affect growth performance differently, how- et al. (1999) reported that as pigs per pen increased ever, water quality is known to influence diarrhea without increasing water sources, total drinking scours and appearance of looseness (Maenz et al., time per pig decreased and drinking bouts termin- 1994; Flohr et al., 2014). ated by aggression increased. Therefore, offering more water access points could minimize low water Diet Considerations intake, subsequently improving FI; however, water access location within the pen should be considered. Feeding a nutrient dense, highly palatable, and Water intake, similar to feeding, is a social ac- readily digestible diet is necessary to stimulate nu- tivity (Torrey and Widowski, 2006), and may be as- trient intake and weanling pig growth. The ad- sociated with an attempt to satisfy hunger by gut vancements made in understanding GI metabolism Translate basic science to industry innovation Wensley et al. have led to a wide range of feed ingredients that treatment differences between liquid and solid feed- target enhancing the naïve pig’s innate and adap- ing programs. However, these data indicate that tive immune responses, reducing pathogen loads liquid feeding may have added benefits for light- and the occurrence of post-weaning diarrhea, weight or early weaned pigs. Regardless, liquid feed- encouraging microbial growth, and stimulating di- ing strategies offer opportunities to increase DM gestive maturation immediately after weaning (de intake in the immediate post-weaning period prior Lange et al., 2010). All of which impacts nutrient to solid feed consumption. This provides newly intake and subsequent growth performance. Some weaned pigs with a continued energy supply neces- of these nutritional strategies include diet acidifi- sary for cognitive function and GI development. cation, fiber, and crude protein content, fatty acid Conversely, offering liquid feed immediately after (FA) supplementation, and functional amino acid weaning may require a “second weaning” period inclusion (AA). Additionally, the effect of liquid when pigs are transitioned from liquid diet to solid feeding and diet form, as well as diet complexity feed. Limited research surrounding the potential and palatability have been considered and offer adverse effects associated with a second weaning opportunities to improve FI in the immediate have not been conducted but should be considered. post-weaning period. Diet form. Common diet forms fed to weanling Liquid feeding. Liquid feeding stimulates GI de- pigs are meal, pellet, or crumble. Feed efficiency is velopment in newly weaned pigs, with a linear cor- often improved with pelleted diets as compared to relation observed between villous height and DM meal diets (Traylor et  al., 1996; Groesbeck et  al., intake (Pluske et  al., 1996b), and ADG (Pluske 2009; Nemechek et al., 2015). There is limited pub- et  al., 1996a). During the first 3 d post-weaning, lished research available on the effects of feeding pigs provided ewes milk or a liquid milk replacer crumble diets compared to meal or pelleted diets. diet had increased DM intake compared to those Medel et  al. (2004) also observed increased nu- offered starter feed; however, by d 5 DM intake trient digestibility when pigs were provided pel- was greatest for pigs consuming the dry starter feed leted diets. Likewise, steam cooking cereal grains (Pluske et  al., 1996a; Bergstrom and McKilligan, prior to grinding and pelleting has been shown to 2006). If producers are able to improve DM in- improve nutrient digestibility and ADG of pigs in take, particularly in the lightweight population, the immediate post-weaning period (Medel et  al., Bergstrom and McKilligan (2006) showed that 2004). It is well established that particle size also there may be an opportunity to decrease death loss influences nutrient digestibility and growth per - and culling rates in the immediate post-weaning formance in nursery pigs (Goodband et  al.,1995), period. Liquid feeding can also be applied to im- as well as feed preference (Bokelman et  al., 2015; prove ADG in pigs weaned younger than 21 d of Gebhardt et  al., 2018). For meal diets, a particle age (Kim et al., 2001). In an attempt to compare the size of 600 μm is known to improve feed efficiency, effectiveness of lactose versus protein in preserving whereas for pelleted diets, a particle size as fine mucosal integrity, Spreeuwenberg et  al. (2001) fed as 350 μm has been reported to improve feed ef- a low lactose/high protein- or high lactose/low pro- ficiency (De Jong et  al., 2014). More importantly tein-liquid milk replacer diet for 4 d post-weaning. for young pigs, diet form effects feed preference The authors observed that pigs offered the high which is influenced by particle size, ingredient lactose/low protein milk replacer tended to have composition, and manufacturing processes (Sola- increased villous length and decreased intestinal Oriol et al., 2009; De Jong et al., 2014). Regardless permeability. However, the effect of diet compos- if fed as mash or pellets, pigs prefer to consume ition on mucosal integrity was less important than diets manufactured with coarser (700 μm) ground the low energy intake observed in both treatment corn (Bokelman et al., 2015; Gebhardt et al., 2018). groups. Fermented liquid feeds is another strategy Furthermore, coarse ground mash diets may offer that may offer potential benefits by helping to de- GI benefits by lowering stomach pH and reducing crease stomach pH through lactic acid production, the incidence of pathogenic bacteria (Vukmirovic thereby inhibiting the growth of pathogenic organ- et  al., 2017). Similarly, research shows that young isms (Moran, 2001). However, Lawlor et al. (2002) pigs prefer pellets with a large diameter (12  mm) observed no added benefit from feeding weanling compared to smaller pellets (van den Brand et al., pigs a fresh liquid milk replacer or fermented liquid 2014). In fact, Clark et  al. (2015) observed that diet, as compared to a standard dry pelleted diet. feeding a large pellet immediately post-weaning In summary, due to low FI immediately increased FI, regardless of previous creep feed post-weaning, researchers often struggle to detect pellet size. In agreement with this data, others have Translate basic science to industry innovation Continuity of nutrient intake after weaning observed irrespective of pellet diameter provided oats having the highest preference during the nur- after weaning, pigs exposed to large creep pel- sery phase. Furthermore, the authors observed fish lets pre-weaning exhibit improved FI and growth meal, soybean meal and spray dried porcine blood post-weaning (van den Brand et  al., 2014). These plasma to have the highest preference of protein data suggest a relationship between diet form and sources which was, greater than that for dried skim particle size when offered both pre- and post-wean- milk. Specifically, dried porcine solubles has a large ing on preference and FI. mean particle size (Sola-Oriol et  al., 2009), which Palatability.  Young pigs are sensitive to palat- may explain the preference for this ingredient. While ability, which therefore drives consumption pref- palatability of feed ingredients should be taken into erences. Undoubtedly, odor and taste play an account when formulating diets for weanling pigs, it important role in palatability (Sola-Oriol et  al., is important to note that preference doesn’t always 2009). Nowicki et  al. (2015) observed that objects equate to higher FI, especially when pigs are not aromatized with moist soil, grass, and dried mush- given a choice between diets. rooms were more attractive to weanling pigs than Diet complexity.  Diet complexity in the im- synthetic aromas. This study did not investigate mediate post-weaning period can mean many dif- the effect of aroma preference on FI but does offer ferent things, including the addition of cooked potential opportunities for environmental enrich- or heat processed cereal grains, a variety of spe- ment strategies to improve exploratory behavior cialty protein products, and dried milk alternatives. and reduce weaning stress. Furthermore, adding Generally, feeding more complex diets during the flavor enhancers or sweeteners to starter diets im- first week post-weaning improves pig growth and mediately after weaning may encourage solid FI efficiency (Sulabo et al., 2010; Collins et al., 2017). (Torrallardona et al., 2001; Langendijk et al., 2007; However, the initial benefits of providing complex Sterk et  al., 2008). However, the literature is in- diets is quickly diminished as pigs become older. consistent, and data are largely dependent on the Four experiments conducted by Mahan et al. (2004) amount and flavor used, feeding duration, and at demonstrated that pigs had increased initial growth what point flavored feed was introduced to pigs. performance when fed complex diets with lactose Flavor imprinting is another strategy that could until 25 kg BW. Others have reported no improve- be used to reduce weaning stress and encourage FI ment in performance when complex diets were fed after weaning. Oostindjer et al (2010) observed that (Steidinger et al., 2002). Because complex diets are pigs exposed to flavors in the diet of the sow be- often more expensive, Collins et  al. (2017) inves- fore birth and during lactation, then subsequently tigated the economic impacts of diet complexity re-exposing to the same flavor at weaning had in- when fed to light, medium, and heavy weight pigs. creased FI and reduced incidence of stress-related The authors observed that feeding more complex behaviors. Figueroa et al. (2013) also observed that diets was only cost effective for light weight pigs brief contact with a demonstrator pig that recently (<6.5  kg), which was attributed to increased life- consumed flavored feed was enough to change the time performance. Douglas et  al. (2014) showed feeding behavior of naïve observers, enhancing that feeding a high-quality starter regime to the low their preference for flavored feed. These effects may birth weight population improved post-weaning pig be in response to reduced stress due to the pres- performance and increased profitability, whereas ence of a familiar flavor in the post weaning en- there was no effect of starter regime on the average vironment (Oostindjer et  al., 2010). As previously or heavy birth weight population. Similar improve- discussed, feed preferences are also influenced by ments have been observed with increasing lactose diet form and complexity. Sola-Oriol et  al. (2009) in diets for light weight pigs (Mahan et al., 2004). demonstrated that while particle size characteristics These data indicate that light weight pigs or those showed only marginal correlations with feed prefer- less developmentally mature may be better suited ence, the hardness, fragility, and time spent chewing for more complex starter diets. showed a statistically significant negative correl- It is well understood that starter diets are im- ation with FI. This supports the presumption that portant for providing glucose and other essential feed requiring a shorter chewing time may be pre- nutrients to the newly weaned pig. Regardless ferred in weanling pigs. In a series of experiments of composition though, the challenge becomes investigating a variety of common feed ingredients, getting pigs to actually consume feed following Sola-Oriol et al. (2014) determined that cereal grain weaning. Under normal circumstances when en- preference increased as digestible starch increased ergy intake is low, the hypothalamus senses dimin- and crude fiber decreased, with naked or refined ishing plasma glucose concentrations subsequently Translate basic science to industry innovation Wensley et al. inhibiting the mechanistic target of rapamycin acidity and improve weanling pig buffer capacity complex 1 signaling pathway (mTORC1; Takei (Ravindran and Kornegay, 1993). Likewise, re- et  al., 2014). Inhibition of mTORC1 is thought search has demonstrated that diet acidification to elicit an increase in FI (Wiczer and Thomas, helps improve protein digestibility (Ravindran and 2010). Unfortunately, this is often not the case in Kornegay, 1993). Similar to organic acids, the in- the immediate post-weaning period. As discussed clusion of whey or lactose in starter diets helps by Wensley et al. (2020), weaning associated stress lower gastric pH by ensuring continued lactic acid may impair normal hypothalamic activation. This production (Lawlor et al., 2005), thereby reducing suggests a complex relationship between stress the need for diet acidification (Partanen and Mroz, and energy homeostasis, which may impact the 1999). These responses are found to decrease with pig’s decision to consume feed. Amino acid levels, age as GI enzymatic activity develops (Yen, 2001). growth factors, and insulin signaling also regu- The improvement of weanling pig buffer capacity late mTORC1 activity, therefore playing a role in through a better understanding of feed ingredi- a multitude of cellular processes necessary for FI, ents is an area of research that still requires further and subsequent growth and survival (Takei et  al., investigation. 2014). Dietary fiber content is another feeding strategy Influence of diet complexity on GI maturation of interest. Providing insoluble fibers in the diet is and post-weaning diarrhea. Diet composition is cru- known to accelerate digesta passage rates and lower cial to the growth and development of the naïve intestinal bacterial adhesion, which increases fecal pig’s GI system, as well as reducing the occurrence DM, offering an opportunity to reduce post-wean- of post-weaning diarrhea. Soybean meal contains ing diarrhea (Montagne et  al., 2003). Conversely, anti-nutritional factors and allergenic proteins that providing soluble fibers in the diet slows digesta reduce nutrient utilization and lower growth per- passage, increasing the production of short-chain formance following first exposure (Li et al., 1990). fatty acids (SCFA). Specifically, butyrate is a SCFA These effects are often temporary with pigs devel- that can be used as a readily available source of en- oping tolerance after 1–2 weeks (Engle, 1994). ergy for a variety of GI functions (Blaut, 2002), Consequently, specialty animal proteins are fre- including regulation of epithelial cell growth (Liu quently added to nursery starter diets in place of et  al., 2018), and reduced intestinal inflammation soybean meal because they contain highly digest- (Liu, 2015). While data is limited, supplementing ible AA and are often more palatable than plant butyrate may be conditionally important in young protein sources. This helps alleviate the adverse pigs undergoing intestinal maturation while also ex- effects of soybean hypersensitivity by slowly accli- periencing weaning stress. Research evaluating the mating wean pigs to increasing levels of soybean effect of fiber sources often observe no performance meal in the diet. Furthermore, feeding low crude differences (Menegat et  al., 2019a). However, gut protein/AA fortified diets, allows nutritionists the health tends to be positively impacted, with a more opportunity to reduce intact protein sources while pronounced response observed when insoluble fi- concurrently increasing the use of highly digest- bers are fed immediately after weaning (Menegat ible crystalline AA (Wang et  al., 2018). For these et al., 2019a). reason, low crude protein diets have gained atten- Lastly, zinc is commonly added to nursery pig tion over the last decade because of their ability to diets at pharmacological levels to reduce post-wean- effectively lower post-weaning diarrhea (Heo et al., ing diarrhea and improve growth performance 2009). (Hill et  al., 2001). High levels of zinc have also Because suckling pigs are consuming high been shown to positively influence intestinal integ- levels of milk lactose, a precursor for lactic acid, rity and the immune system of weanling pigs (Liu stomach acidification by HCl is inhibited (Cranwell et al., 2018). While the mechanisms of pharmaco- et al., 1976). At weaning, consumption of solid feed logical levels of zinc are largely unknown, Ou et al. reduces lactic acid production, thereby stimulating (2007) observed that added zinc inhibited stem cell the production of HCl (Yen, 2001). This often leads factor gene expression, which are responsible for to an elevation in gastric pH resulting in reduced di- mast cell proliferation and subsequent histamine gestion of feed and a more favorable environment expression. Mast cell derived histamine has been for pathogenic bacteria, which may incite diarrhea linked to the pathogenesis of diarrhea, indicating (Lawlor et  al., 2005; Wang et  al., 2018). The add- one potential mode of action for added zinc (Ou ition of organic acids to starter diets is a well-recog- et  al., 2007). Copper is another important trace nized feeding strategy used to manipulate stomach mineral that offers improved fecal consistency and Translate basic science to industry innovation Continuity of nutrient intake after weaning growth promoting benefits when added at pharma- diets increased gut microbial diversity and decreased cological levels in nursery pig diets (Menegat et al., body lesions in pigs during immediate post-wean- 2019b). While it’s mode of action is also not well ing period (Parois et al., 2020). Furthermore, added defined, the growth promoting effects of copper L-glutamine resulted in decreased tear staining and have been attributed to its bacteriostatic and bac- greater interest in novel objects. An earlier report tericidal properties (Espinosa and Stein, 2021). showed that lying behavior in the first 2 d after Copper supplementation is also recognized to in- simulated transport was increased in groups that crease lipase activity, stimulate growth hormone se- did not receive antibiotics compared to antibiotic cretion, indirectly improve immune responses, and or L-glutamine fed pigs (Johnson and Lay, 2017). It increase mRNA genes involved in post-absorptive is well established in humans and rodents that mi- metabolism of lipids (Espinosa and Stein, 2021). crobial dysbiosis is associated with depressive and Feed ingredients that may impact GI health anxiety like behaviors (Kelly et  al., 2015), which and FI.  Gastrointestinal health around the time may explain the reduction in aggression, stress, and of weaning is often compromised as a result of fear related behaviors observed in pigs fed added stress and low FI. Fatty acids and other lipids in glutamine (Johnson and Lay, 2017; Parois et  al., sow’s milk are a highly digestible energy source 2020). Together, these data suggest that glutamine frequently not provided in the post-weaning diet has an interactive role on GI health, development, (Lauridsen, 2020). The strategic use of FA supple- and the microbiome-gut-brain axis. While these mentation may benefit the growth and development data suggest a positive response to glutamine when of the GI system through energy maintenance, es- fed in nursery starter diets, widespread adaptation pecially while under inflammatory conditions (Liu, of glutamine supplementation has not been seen. 2015). Trials conducted in rats and humans have Glutamine has not approved for feeding in all loca- demonstrated that diets enriched with omega-3 tions globally. polyunsaturated FA may help downregulate meta- Tryptophan (Trp) is an essential AA that acts bolic factors associated with glucose depletion and as a precursor for the neurotransmitter serotonin, GI inflammation (Barber et al., 1999; 2001; Huber which is associated with mood, sleep and appetite et al., 2018). Adding dietary FA post-weaning, may regulation (Le Floc’h and Seve, 2007). It is well provide opportunities to improve pig health and established that diets deficient in Trp reduce FI. increase nutrient utilization, particularly in health Furthermore, when pigs are exposed to inflamma- challenged systems. tory, immune or environmental stressors, serotonin Glutamine is a conditionally essential AA catabolism in the brain increases (Takeda et  al., that has been also been identified for its role in 2004). This mechanism is designed to help prevent GI function (Lewis, 2001). Specifically, glutamine mood disturbances and depressive disorders; how- is recognized as the primary energy source for in- ever, it may lead to a shortage of serotonin as ex- testinal enterocytes (Wu et  al., 1996). When sup- penditure exceeds synthesis (Takeda et  al., 2004). plemented in starter diets at 1%, L-glutamine has These effects may be intensified when FI is limited been shown to prevent jejunal atrophy during the (Le Floc’h and Seve, 2007). Supplemental Trp has first week postweaning (Wu et  al., 1996), increase been reported to reduce stress hormone concen- intestinal cell proliferation, and reduce the ex- trations, which may be beneficial in the immediate pression of genes associated with oxidative stress post-weaning period (Koopmans et  al., 2005; Liu (Wang et al., 2008). Similarly, others have demon- et al., 2013). Early research has indicated that Trp strated the importance of glutamine on tight junc- may also modulate plasma insulin secretion and tion protein regulation and CRF expression (Wang sensitivity (Cortamira et  al., 1991), suggesting a et  al., 2015). In support of these findings, earlier role in glucose metabolism. Increasing dietary Trp reports indicate that glutamine may become con- also induces high ghrelin levels along the GI tract ditionally essential in times of immune system ac- (Zhang et  al., 2007). Ghrelin is a 28-AA peptide tivation, particularly during stress when the body’s hormone secreted from the stomach that is involved glutamine requirement appears to exceed its rate of in the mTOR signaling pathway and is believed to production (Lacey and Wilmore, 1990). Duttlinger regulate FI in response to serotonin levels (Zhang et al. (2019) showed that after a 12 h transport, re- et al., 2007; Nørgaard et al., 2015). placing dietary antibiotics with 0.20% L-glutamine Sodium and chloride are also of particular improved pig performance and health during the importance for nursery pigs. These minerals, first 14 d after placement. Under similar transport commonly fed in the form of salt, are involved conditions, L-glutamine supplementation in starter in nutrient absorption, electrolyte balance, and Translate basic science to industry innovation Wensley et al. regulation of pH (Menegat et  al., 2019b). Diets • Liquid feeding/milk replacer: Liquid feeding that are deficient in salt result in decreased growth strategies do offer opportunities to increase DM performance due to reduced FI and poor feed ef- intake in the immediate post-weaning period, ficiency (Shawk et al., 2018a, b). For 5–7 kg wean- particularly in lightweight pigs. The implications ling pigs, providing 0.4% and 0.5% sodium and on death loss and culling rates need to be con- chloride, respectively is necessary to meet their sidered. Does offering liquid feed immediately requirement. after weaning require a second weaning period Enzymes are another area commonly studied, when pigs are transitioned from the liquid diet to with phytases contributing the greatest benefit. solid feed? While phytase is not known for increasing FI, it • Delayed feeding: Does delayed feeding offer an is well established that adding exogenous phytase opportunity for pigs to get acclimated with a new to swine diets helps improve phosphorus avail- environment and pen mates, prior to feed stim- ability. Compared to standard doses (<1,000 FTU), uli? Would the sound of feed being dropped into super-dosing phytase (<2,000 FTU) has been shown feeders encourage feed behavior? And how long to provide additional benefits beyond phosphorus of a delay is too long? release, which may be attributed to the release of • Diet form: Influence of crumble diets on pig inositol from the phytate complex. Moran et  al. feeding preference and growth performance, (2019) demonstrated that increasing exogenous compared to meal and pellet diets. inositol improved feed efficiency in pigs fed diets • Diet palatability: More research is needed on without phytase, equivalent to the improvement the concept of early flavor experiences. Does observed with super-dosing phytase. Following the perinatal or social interaction flavor learning in- immediate post-weaning period, FI increased as in- crease feed acceptance post-weaning as a result ositol supplementation increased in the absence of of flavor association? phytase. Though the mode of action is unknown, • Diet considerations: More research is still needed this suggests that inositol may be conditionally es- to determine the effect high fiber and low crude sential in diets of weanling pigs. Croze and Soulage protein, AA fortified diets on post-weaning diar - (2013) suggest that myo-inositol has a role in insulin rhea and growth performance. signaling and protein synthesis, possibly improving glucose metabolism and contributing to improved performance. CONCLUSION Weaning older, heavier pigs and encouraging Gaps in Knowledge feeding behavior through environmental and nu- Reducing nutrient disruption after weaning can tritional strategies will help improve FI and early be accomplished through further exploration of growth immediately after weaning. According to a multiple post-weaning strategies. Understanding study conducted by Pluske (2013), husbandry and the long-term implications of these strategies is also management techniques, including hygiene and crucial. education, offer the greatest potential for reducing nutrient disruption at the time of weaning. Several • Thermoneutral zone: What environmental tem- factors are known to influence nutrient intake after peratures are ideal, in accordance with season, weaning including: to encourage pen exploration and reduce latency to first feeding? • Feed availability: Easy access to feed improves • Feed availability: Mat and gruel feeding are com- immediate post-weaning FI. This is influenced monly practiced throughout the industry; how- by pen size, group size, feeder design, and loca- ever, limited data is available to document the tion of feeder relative to water. value of these feeding strategies. • Water quality: High levels of dissolved minerals • Water availability: More research in commercial in the water do not hinder performance but may settings with larger group sizes is needed to de- influence diarrhea scours and appearance of termine adequate water space. Additionally, how looseness. does wet/dry feeding impact water space require- • Water enrichment: Water enrichment strategies ments? And how does feeder arrangement rela- do provide additional nutrients that have been tive to drinker location affect FI and subsequent shown to benefit growth performance and mor - performance. bidity and mortality when FI is low. Translate basic science to industry innovation Continuity of nutrient intake after weaning patients with pancreatic cancer. Br. J.  Cancer 81:80–86. • Nursery placement: Sorting pigs into uniform doi:10.1038/sj.bjc.6690654 BW groups is beneficial for light weight pigs but Bergstrom,  J., and D.  McKilligan. 2006. An evaluation of li- not heavy weight pigs. quid feeding immediately post-weaning to improve the • Diet form: For young pigs the implication of diet performance of the lightest pigs within a nursery group. form on palatability preference is an important Allen D. Leman Swine Conference, Minneapolis, MN. Blaut,  M. 2002. Relationship of prebiotics and food intes- consideration. Pelleted diets increase feed effi- tinal microflora. Eur. J.  Nutr. 41:11–16. doi:10.1007/ ciency and nutrient digestibility compared to s00394-002-1102-7 meal diets. Regardless if fed as a meal or pellet Bokelman,  G.  E., J.  A.  De  Jong, J.  R.  Kalivoda, A.  Yoder, though, weanling pigs prefer diets manufactured C. R. Stark, J. C. Woodworth, and C. K. Jones. 2015. Finely with coarse (700  μm) ground corn rather than grinding cereal grains in pelleted diets offers little improve- fine ground corn. When pelleted diets are fed ment in nursery pig growth performance. Kansas Agric Exp Station Res Rep. 1:17. doi:10.4148/2378–5977.1122 however, young pigs prefer pellets with a larger van  den  Brand,  H., D.  Wamsteeker, M.  Oostindjer, diameter. L. C. M. van Enckevort, A. F. B. van der Poel, B. Kemp, and • Diet complexity: Feeding more complex diets J.  E.  Bolhuis. 2014. Effects of pellet diameter during and during the first week post-weaning improves pig after lactation on feed intake of piglets pre- and postwean- growth and efficiency, with the greatest response ing. J. Anim. Sci. 92:4145–4153. doi: 10.2527/jas2014-7408 Brooks, P. H., S. J. Russell, and J. L. Carpenter. 1984. Water in- observed in the lightweight pig population. The take of weaned piglets from three to seven weeks old. Vet. initial benefits observed in performance tend to Rec. 115:513–515. doi:10.1136/vr.115.20.513 decrease with increasing time post-weaning. Brooks,  P.  H., and C.  H.  Tsourgiannis. 2003. Factors af- • Diet palatability: Young pigs are sensitive to pal- fecting the voluntary feed intake of the weaned pig. atability which is influenced by odor, taste, and In: J.  Le  Dividich, J.  R.  Pluske, M.  W.  A.  Verstegen, texture. Therefore, feed ingredients should be editor, Weaning the Pig: Concepts and Consequences. Wageningen, Netherlands: Wageningen Academic taken into account when formulating diets for Publishers. p. 81–116. newly weaned pigs. Increased preference doesn’t Bruininx,  E.  M.  A.  M., C.  M.  C.  van  der  Peet-Schwering, always equate to higher FI, especially when pigs J. W. Schrama, P. F. G. Vereijken, P. C. Vesseur, H. Everts, are not given a choice between diets. L.  A.  den  Hartog, and A.  C.  Beynen. 2001. Individually • Diet ingredients and nutrients: Organic acid supple- measured feed intake characteristics and growth perform- ance of group-housed weanling pigs: effects of sex, initial mentation, crude protein level, insoluble fiber in- body weight, and bodyweight distribution within groups. clusion, and zinc and copper concentrations alter J. Anim. Sci. 79:301–308. doi: 10.2527/2001.792301x the occurrence of post-weaning diarrhea. Fatty ac- Carey, H. V., U. L. Hayden, and K. E. Tucker. 1994. Fasting al- ids and functional AA such as glutamine and Trp ters basal and stimulated ion transport in piglet jejunum. positively influence gut health and subsequent FI. Am. J.  Physiol. 267(1 Pt 2):R156–R163. doi:10.1152/ Salt concentrations also play an important role in ajpregu.1994.267.1.R156 Clark, A. B., J. A. De Jong, J. M. DeRouchey, M. D. Tokach, FI and palatability preferences, with myo-inositol S. S. Dritz, R. D. Goodband, and J. C. Woodworth. 2015. having more recent implications on FI. Effects of creep feed pellet diameter on suckling and nur- sery pig performance. Kansas Agric Exp Station Res Rep. ACKNOWLEDGMENTS 8:13. doi:10.4148/2378–5977.1118 Collins, C. L., J. R. Pluske, R. S. Morrison, T. N. McDonald, Contribution no.  21-114-J from the Kansas R. J. Smits, D. J. Henman, I. Stensland, and F. R. Dunshea. Agricultural Experiment Station, Manhattan, 2017. Post-weaning and whole-of-life performance of pigs 66506-0201. Appreciation is expressed to TechMix is determined by live weight at weaning and the com- plexity of the diet fed after weaning. Anim. 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In A.  J.  Lewis and L.  L.  Southern, domaniend.2006.04.005 Translate basic science to industry innovation http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Translational Animal Science Oxford University Press

Maintaining continuity of nutrient intake after weaning. II. Review of post-weaning strategies

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Maintaining continuity of nutrient intake after weaning. II. Review of post-weaning strategies †,1 † † † Madie R. Wensley, Mike D. Tokach, Jason C. Woodworth, Robert D. Goodband, ‡ † || Jordan T. Gebhardt, Joel M. DeRouchey, and Denny McKilligan Department of Animal Sciences and Industry, College of Agriculture, Manhattan, KS 66506-0201, USA; Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, || Manhattan, KS 66506-0201, USA; and TechMix Inc., Stewart, MN 55385, USA ABSTRACT:  Low feed consumption during the aggression in heavy pigs. Furthermore, water en- first 3 d post-weaning disrupts nutrient intake and richment with nutrient dense products have been results in what is commonly known as a post-wean- shown to improve growth performance and reduce ing growth check. While most pigs recover from morbidity and mortality in the early post-weaning this initial reduction in feed intake (FI), some pigs period. Because young pigs are sensitive to palat- fail to successfully make this transition leading to ability, diet form and complexity should also be morbidity and mortality. In this review, our ob- considered. Weanling pigs prefer diets manufac- jective is to describe the different post-weaning tured with coarse ground corn (700  μm) com- strategies that can be used to minimize nutrient pared to fine ground corn. Additionally, weanling intake disruption and improve FI in the imme- pigs are more attracted to large diameter pellets diate post-weaning period. Providing weanling (12  mm) compared with small pellets. Despite pigs with an environment that encourages them to these preferences, impacts on growth are relatively search out and consume feed is important. This small. Feeding complex diets with high levels of includes appropriate barn temperatures, resource lactose, animal protein products, or other palat- availability, and nursery placement strategies. able ingredients is another strategy shown to im- Research is needed to better understand the ideal prove growth performance during the first week environmental temperatures to encourage pen ex- post-weaning; however, the initial benefits quickly ploration and reduce time to initial FI. Likewise, diminished as pigs become older. Other strategies mat and gruel feeding are commonly practiced that warrant further investigation include the ef- throughout the industry to increase feed accessi- fect of crumble diets on feed preference and the bility; however, limited research data is available to concept of perinatal or social interaction flavor validate protocols or benefits. Nursery placement learning. In summary, strategic post-weaning nu- strategies include sorting light weight pigs into trition and management practices must focus on uniform body weight groups and average or heavy maintaining continuity of nutrient intake in order weight pigs into variable body weight groups to to reduce morbidity and mortality in the imme- provide benefit to light pigs while reducing initial diate post-weaning period. Key words: feed intake, nutrient disruption, pig, post-weaning © The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. This is an Open Access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Transl. Anim. Sci. 2021.5:1-16 doi: 10.1093/tas/txab022 Corresponding author: wensleym@ksu.edu Received November 20, 2020. Accepted February 2, 2021. 1 Wensley et al. INTRODUCTION for FI after weaning. Factors that have a significant impact on post-weaning behavior and consequently In modern swine production, weaning often oc- FI, include barn temperatures, agonistic behavior curs during a critical window of gut maturation, or hierarchy establishment, lack of feeding stimuli, marked by increased epithelial function, microbiota feed palatability, and resource availability (Brooks colonization, immune cell proliferation, and enteric and Tsourgiannis, 2003), many of which will be nervous system development (Moeser et al., 2017). covered herein. Furthermore, the transition from Excessive immune stimuli in response to weaning a single milk-based diet (sow’s milk) to separate stressors during this period has been linked to im- feed and water sources, requires an abrupt learn- paired neurodevelopment (Kelly et  al., 2015) and ing period that pigs must adapt to after weaning gastrointestinal (GI) maturation (Moeser, 2016; in order to familiarize themselves with the differ- Pluske, 2016). Williams et  al (1997) also reported ence between hunger and thirst satiety (Brooks and a reduction in feed intake (FI), low protein accre- Tsourgiannis, 2003). It is for this reason that water tion, and diminishing body leanness as a result of consumption remains elevated for the first several chronic immune system activation. Inflammatory days post-weaning (Brooks et al., 1984). However, cytokines which are released in response to immune once feed is discovered and pigs become more com- stimuli are known to further suppress appetite and fortable in their new environment, normal eating inhibit nutrient absorption (Escobar et  al., 2004). and drinking patterns are established (Brooks et al., In herds under chronic disease challenge, prolonged 1984). production of cytokines induces muscle and fat ca- The question then becomes how we can increase tabolism, as well as impaired carbohydrate metab- exploratory behavior and encourage FI early after olism (Matthys and Billiau, 1997; Escobar et  al., weaning. In an attempt to investigate the social 2004). This deterioration in energy metabolism learning behavior of piglets after weaning, Morgan can be detrimental to the central nervous system, et  al (2001) observed that experienced eaters were altering the brains ability to function properly able to stimulate earlier feeding behavior in wean- and elicit physical responses to stimuli, including ling pigs who were unfamiliar with solid feed. When the newly weaned pigs’ decision to search out and housed in the same pen as experienced eaters, inex- consume feed. perienced eaters exhibited increased FI and more Low FI after weaning reduces the flow of nutri- frequent visits to the feeder, compared to pens that ents through the GI track, resulting in what is com- housed only inexperienced eaters. These results in- monly known as a post-weaning growth check. This dicate a potential mechanism where eating behavior period is marked by body weight (BW) loss and in- and exploration is learned by non-eaters from those testinal disturbances that lead to a high occurrence already consuming feed. Pairing inexperienced of GI inflammation (McCracken et  al., 1999) and eaters with those familiar with solid feed may also diarrhea. While most pigs recover from the initial encourage the pigs innate drive for synchronized reduction in FI, some pigs fail to successfully make feeding like suckling; however, this has not been this transition leading to morbidity and mortality. fully proven. Interestingly, recent data suggests that The objective of this review is to describe the dif- the day of weaning may not be the best time for pigs ferent post-weaning strategies to minimize nutrient to discovery solid feed, due to the stress of weaning intake disruption and improve FI in the immediate on the pigs learning ability (Millet et al., 2019). The post-weaning period. authors investigated the effect of allowing newly weaned pigs an opportunity to rest (18 h) and get acclimated with their new environment before feed Post-weaning FI was provided in the pen. Pigs that received feed 18 h The primary limiting factor affecting FI in newly after weaning had increased FI and average daily weaned pigs is their physical capacity to ingest feed gain (ADG) from d 0 to 21 compared to pigs that (Li and Patience, 2017). Therefore, low FI immedi- received feed at weaning. This feed management ately post-weaning often does not provide enough strategy could offer a way to synchronize pigs to eat nutrients to the pig to satisfy maintenance require- together, stimulating pigs to search out feed when ments, subsequently leading to reduced growth. they hear it dropped into feeders. This concept re- However, it is important to understand what fac- quires more research. Nonetheless, it is apparent tors are involved in the regulation of FI in newly that behavior plays a crucial role in initial FI. weaned pigs in order to develop successful manage- While external stressors tend to be additive in ment and feeding programs to better prepare pigs their negative effects (Hyun et  al., 1998), it is well Translate basic science to industry innovation Continuity of nutrient intake after weaning established that increasing nutrient intake after wean-to-finish facilities with large pens sizes, can weaning can minimize stress associated losses in help accomplish a range of temperature zones that intestinal barrier function (Wijtten et  al., 2011; are suitable for pigs of all sizes. When temperatures Verdonk, 2006). Consequently, feed deprivation reach the upper boundary of the thermoneutral (72 h) has been reported to alter the endocrine and zone, pigs will often search out cool, damp places neuroendocrine axis and hypothalamic pituitary to lay, spreading out across the pen in an attempt to adrenal (HPA) axis hormones, negatively influ- avoid contact with other pigs. As a result, pigs will encing FI (Salfen et  al., 2003). Stress conditions, often decrease FI and increase water consumption. such as those surrounding the time of weaning In contrast, when temperatures reach the lower are thought to suppress feed consumption due to boundary of the thermoneutral zone, pigs will the anorectic effects of corticotropin release factor often pile close together and if they have already (CRF, Pelleymounter et al., 2000). As a result, ab- found feed, will increase FI to compensate for en- sence of nutrients to the lumen has been shown to ergy used to maintain body heat (NRC, 1981). This increase active ion transport across the epithelial, may be less of a concern immediately after weaning an indicator of intestinal permeability (Carey et al., because many pigs have not yet identified feed. 1994). Likewise, increased intestinal permeability Thus, temperatures below the thermoneutral zone can reduce nutrient absorption capacity (Moeser may instead prevent weanling pigs from searching et  al., 2017), therefore leading to lower BW gain out feed. For these reasons, it is essential that care- (Pluske et al., 2013). takers provide an adequate thermal environment In summary, there are several external and that encourages weanling pigs to discover feed. internal factors that influence FI after weaning. Resource availability.  Providing weanling pigs Consequently, low FI results in decreased intestinal easy access to resources like feed and water is im- barrier function and villous atrophy, followed by portant. Increasing resource availability includes a a period of BW loss that often takes several days variety of management practices for offering pigs from which to recover (Reviewed by Brooks and feed and water, such as feeder design, wet and dry Tsourgiannis, 2003). Therefore, maintaining a con- feeding systems, mat or gruel feeding, as well as tinuous supply of nutrients post-weaning is crucial drinker access. to minimizing the post-weaning growth check and Pluske and Williams (1996) tested the hypoth- ensure a more successful weaning transition. esis that providing water in addition to feed from a single space, wet/dry feeder would stimulate FI com- pared to a single space, dry or multi-space feeder. POST-WEANING STRATEGIES TO However, the use of wet/dry single space feeders re- INCREASE FI AFTER WEANING duced gain in the first week after weaning. The au- thors observed that pigs had difficulty learning how to manage the wet/dry feeder, often filling the bowl Environmental Factors Influencing Nutrient Intake with excess water. It is important to note that pigs After Weaning per feeder space were not considered in this study. Thermoneutral zone.  Caretaker understanding More recently, it was reported that decreasing the of the thermoneutral zone, or effective tempera- number of pigs per feeder hole decreased time to ture, is important in order to prevent heat or cold feeding. Pens of pigs with 3.75 pigs per feeder hole stress of pigs at the time of weaning. In addition began consuming feed approximately 8  h earlier to room temperature, other environmental factors compared to pens of pigs with 6.25 pigs per feeder impacting effective temperature include heat loss hole (Laskoski et al., 2019). via convection, conduction, and radiation which Mat feeding in addition to standard trough in turn are affected by air movement, floor type, feeding has been reported to reduce morbidity and building insulation (Baker, 2004). Other con- and mortality during the first 3-weeks post-wean- tributing factors to the effective temperature in- ing (Corrigan, 2000; Potter et al., 2010). Similarly, clude air quality and humidity (Lammers et  al., there is evidence that gruel feeding pigs reduces 2007). According to PIC’s wean-to-finish guidelines morbidity compared to pigs offered only dry (2019), the recommended barn temperature for pigs feed (Corrigan, 2000). In a series of experiments, at weaning ranges from 23 to 29 °C depending on Corrigan (2000) observed that both gruel and the use of zone heating. The use of zone-heating mat feeding increased feed disappearance, but such as brooders, heat lamps, and floor mats dur - largely due to increased feed wastage. Potter et al. ing the first weeks post-weaning, particularly in (2010) observed a similar response, with mat-fed Translate basic science to industry innovation Wensley et al. pigs exhibiting poorer feed efficiency, particularly also observed less agonistic behavior in groups of when mat-fed for 7 d as compared to 3 d after pigs that came from the same litter. These data are weaning. However, mat feeding increased eating inconsistent with earlier reports that showed mix- behavior the first day after weaning (Corrigan, ing unfamiliar pigs at weaning actually promotes 2000) and resulted in fewer pig removals during FI and improves growth rate (Pluske and Willams, the nursery period (Potter et al., 2010). Providing 1996). pigs feed in the for m of a gruel increased consump- Another strategy that has been evaluated is tion but reduced eating and drinking behavior at sorting by sow parity. Because gilt progeny often the feeder and drinker. Thus, gruel should not be have poorer lifetime performance compared to used to meet all the feeding requirements. Rather, sow progeny, Craig et  al (2017) hypothesized it is recommended gruel be provided intermit- that segregating gilt and sow progeny at place- tently (3–4 times daily) as to still encourage dry ment would improve the growth and survival of FI. This is to prevent pigs from needing a second both groups. However, this strategy resulted in no transition to get them to the feeder once gruel added benefits. feeding has ended. Generally, gruel is prepared As group size increases, the number of dyadic with equal amounts of water and solid feed; relationships a pig must establish also increases however, the amount of gruel prepared often de- (Turner and Edwards, 2004). This suggests that pends on the number of pigs per pen and should there is more opportunity for aggressive behavior only be enough to last a short period of time to between pigs when attempting to establish social prevent feed spoilage. Depending on the health hierarchy. However, Turner and Edwards (2004) status of pigs receiving gruel feed, intensive care observed no elevation in aggressive tendencies as supplements which are highly palatable and often group size increased above 50 pigs per pen com- aromatic can be added to the gruel to further en- pared with a more conventional group size (10–30 courage FI. Similar to the events surrounding pigs). In an earlier review, Turner et  al. (2003) re- suckling, mat or gruel feeding after weaning may ported that as group size increased, weanling pigs help stimulate group feeding behavior; however, had significant reductions in ADG due to decreased more research is needed to fully understand the FI. It is important to note that group number and implications of mat and gruel feeding strategies. space allowance ranged from 3–120 pigs per pen and 0.186–0.74 m per pig, respectively. These re- sults are consistent with previous findings, in which Sorting Pigs at Nursery Placement reduced oor fl -space allowance reduced pig growth Nursery placement strategies influence pig be- performance during the nursery period (Wolter havior and latency to first FI. While weaning into et  al., 2000a). It has also been suggested that re- variable versus uniform BW groups has shown to source placement may affect feeding behavior, par- have little effects on overall performance, heavy ticularly in large groups. To quantify the effect of weight pigs in uniform groups have lower initial FI feeder location on the performance of weanling than heavy weight pigs in variable weight groups pigs, Wolter et  al. (2000b) evaluated two pen de- (Bruininx et al., 2001). More recently, Faccin et al signs using either five two-sided feeders in a single, (2019) observed increased aggressive behavior and central location or five two sided feeders in multiple delayed FI in pens sorted into all heavy pigs com- locations throughout the pen. The use of multiple pared to pens sorted into light or medium weight feeder locations in a large group pen design did pigs. It is likely that heavy pigs spend more time not increase FI or growth. Additional research is establishing dominance than consuming feed. Sex needed to better characterize the eating behavior of also has a known impact on the behavior and per- pigs in different group sizes and spacing allowances, formance of pigs at placement. Bruininx et  al and how feeder arrangement relative to drinker lo- (2001) observed that gilts had increased FI and cation may affect FI and subsequent performance. gain compared to barrows during the first week In summary, these data suggest that sorting after weaning. Similarly, initial mixing aggression light weight pigs into uniform groups may be bene- tended to decrease when sorting groups of pigs by ficial, while remaining pigs should be randomly gender (Colson et  al., 2006). Furthermore, data placed without sorting by weight to reduce aggres- indicates that pigs weaned into familiar groups sion in the heavy weight pigs. In addition to BW, consume more feed and grow faster the first week sorting by sex or socializing pigs prior to weaning post-weaning than pigs weaned into unfamiliar reduces initial aggression and may also increase FI groups (Turpin et  al., 2017). Hwang et  al. (2016) and immediate post-weaning growth. Translate basic science to industry innovation Continuity of nutrient intake after weaning Water Consumption and Enrichment fill immediately after weaning (Torrey et al., 2008). In a series of experiments, Torrey and Widowski The recommended water requirement for nursery (2004, 2006) and Torrey et  al. (2008) investigated pigs up to 27.2 kg BW is 2.8 L per pig per day (NPB, different drinker types on pig preference, intake 2003), which equates to 2.5–3 L per kg of feed con- and wastage. Nipple drinkers resulted in increased sumed. However, in the first 5 d post-weaning, water water wastage and belly nosing behavior compared consumption is typically not linked to FI or physio- to push-lever bowl drinkers (Torrey and Widowski, logical need but rather weaning influenced consump- 2004; Torrey et  al., 2008). The authors suggest tion patterns (previously discussed; McLeese et  al., that motor patterns involved with ingesting water 1992). Water intake tends to be the greatest in the first from bowl drinkers may mimic suckling stimuli 24  h, suggesting dietary supplements may be more that satisfies nosing motivation; therefore, decreas- beneficial when administered through the water rather ing belly nosing behavior. Furthermore, pigs with than feed (Dybkjær et  al., 2006). Options to enrich bowl drinkers spent more time at the feeder. This the water include acidification (De Busser et al., 2011; is in contrast to a later study that indicated pigs Escuredo et  al., 2016), plasma-based globulin prod- with push-lever bowls spent less time at the feeder ucts, glucose or lactose-based energy products, elec- (Torrey et al., 2008). Despite water usage and time trolytes, or a combination of enrichments (Steidinger spent at the feeder, drinker type did not influence et  al., 2002; Myers et  al., 2011; Morris et  al., 2017; FI or ADG. When given a choice between different Schmitt et al., 2018). Studies have reported improved drinker types, weanling pigs found nipple and growth performance in the early post-weaning period oa fl t bowl drinkers faster than push-lever drinkers when water-soluble sources of animal plasma protein (Torrey and Widowski, 2006). Throughout the dur- and energy are provided in the drinking water, with ation of the study, pigs continued to prefer nipple diminishing results thereafter (Steidinger et al., 2002; and float bowl drinkers over push-lever bowls, Vande Pol et al., 2017). Reductions in morbidity and which may be due to easier water access. Based on mortality have also been observed with water enrich- these three experiments, the authors recommend ment (Morris et al., 2017; Schmitt et al., 2018). While the use of push-lever bowl drinkers to prevent ex- most water enrichment strategies are administered cessive water wastage while not negatively affecting during the first 3 to 7 d post-weaning, timing and dur - FI and BW gain (Torrey et al., 2008). ation of administration may influence efficacy. It is also important to consider the impact of According to the Swine Housing and Equipment water quality, particularly sulfate concentrations Handbook (MWPS, 1983), there should be 10 and total dissolved solids, on water and feed con- nursery pigs per nipple drinker space; however, a sumption. Patience et al. (2004) observed that sul- ratio of 25:1 is more common in the US industry fate levels up to 1,650 mg/L did not hinder growth (Jackson, 2007). Because too few waterers can re- performance. Flohr et  al (2014) observed that duce water intake and consequently FI, Jackson adding sodium sulfate at higher levels (3,000 mg/L) (2007) investigated the effect of increasing water resulted in a significant impact on growth perform- access in pens of 25 pigs. When pigs were offered ance. Conversely, earlier reports suggest that water more places to drink, they visited the water bowl containing high levels of total dissolved solids more frequently. This tended to increase ADG (4,390 mg/L, 2,650 mg of SO /L, 947 mg of Na/L, throughout the nursery period. Interestingly, pigs 288  mg of C/L, 88  mg of Mg/L, 70  mg of Cl/L, demonstrated drinker location preference with the and 15 mg of K/L) may actually promote water and alley waterer receiving the fewest visits compared to FI during the first 10 d post-weaning (Maenz et al., waterers located on the same side of the pen as the 1994). High levels of sulfate and dissolved solids feeder or on the back wall. Furthermore, Turner may affect growth performance differently, how- et al. (1999) reported that as pigs per pen increased ever, water quality is known to influence diarrhea without increasing water sources, total drinking scours and appearance of looseness (Maenz et al., time per pig decreased and drinking bouts termin- 1994; Flohr et al., 2014). ated by aggression increased. Therefore, offering more water access points could minimize low water Diet Considerations intake, subsequently improving FI; however, water access location within the pen should be considered. Feeding a nutrient dense, highly palatable, and Water intake, similar to feeding, is a social ac- readily digestible diet is necessary to stimulate nu- tivity (Torrey and Widowski, 2006), and may be as- trient intake and weanling pig growth. The ad- sociated with an attempt to satisfy hunger by gut vancements made in understanding GI metabolism Translate basic science to industry innovation Wensley et al. have led to a wide range of feed ingredients that treatment differences between liquid and solid feed- target enhancing the naïve pig’s innate and adap- ing programs. However, these data indicate that tive immune responses, reducing pathogen loads liquid feeding may have added benefits for light- and the occurrence of post-weaning diarrhea, weight or early weaned pigs. Regardless, liquid feed- encouraging microbial growth, and stimulating di- ing strategies offer opportunities to increase DM gestive maturation immediately after weaning (de intake in the immediate post-weaning period prior Lange et al., 2010). All of which impacts nutrient to solid feed consumption. This provides newly intake and subsequent growth performance. Some weaned pigs with a continued energy supply neces- of these nutritional strategies include diet acidifi- sary for cognitive function and GI development. cation, fiber, and crude protein content, fatty acid Conversely, offering liquid feed immediately after (FA) supplementation, and functional amino acid weaning may require a “second weaning” period inclusion (AA). Additionally, the effect of liquid when pigs are transitioned from liquid diet to solid feeding and diet form, as well as diet complexity feed. Limited research surrounding the potential and palatability have been considered and offer adverse effects associated with a second weaning opportunities to improve FI in the immediate have not been conducted but should be considered. post-weaning period. Diet form. Common diet forms fed to weanling Liquid feeding. Liquid feeding stimulates GI de- pigs are meal, pellet, or crumble. Feed efficiency is velopment in newly weaned pigs, with a linear cor- often improved with pelleted diets as compared to relation observed between villous height and DM meal diets (Traylor et  al., 1996; Groesbeck et  al., intake (Pluske et  al., 1996b), and ADG (Pluske 2009; Nemechek et al., 2015). There is limited pub- et  al., 1996a). During the first 3 d post-weaning, lished research available on the effects of feeding pigs provided ewes milk or a liquid milk replacer crumble diets compared to meal or pelleted diets. diet had increased DM intake compared to those Medel et  al. (2004) also observed increased nu- offered starter feed; however, by d 5 DM intake trient digestibility when pigs were provided pel- was greatest for pigs consuming the dry starter feed leted diets. Likewise, steam cooking cereal grains (Pluske et  al., 1996a; Bergstrom and McKilligan, prior to grinding and pelleting has been shown to 2006). If producers are able to improve DM in- improve nutrient digestibility and ADG of pigs in take, particularly in the lightweight population, the immediate post-weaning period (Medel et  al., Bergstrom and McKilligan (2006) showed that 2004). It is well established that particle size also there may be an opportunity to decrease death loss influences nutrient digestibility and growth per - and culling rates in the immediate post-weaning formance in nursery pigs (Goodband et  al.,1995), period. Liquid feeding can also be applied to im- as well as feed preference (Bokelman et  al., 2015; prove ADG in pigs weaned younger than 21 d of Gebhardt et  al., 2018). For meal diets, a particle age (Kim et al., 2001). In an attempt to compare the size of 600 μm is known to improve feed efficiency, effectiveness of lactose versus protein in preserving whereas for pelleted diets, a particle size as fine mucosal integrity, Spreeuwenberg et  al. (2001) fed as 350 μm has been reported to improve feed ef- a low lactose/high protein- or high lactose/low pro- ficiency (De Jong et  al., 2014). More importantly tein-liquid milk replacer diet for 4 d post-weaning. for young pigs, diet form effects feed preference The authors observed that pigs offered the high which is influenced by particle size, ingredient lactose/low protein milk replacer tended to have composition, and manufacturing processes (Sola- increased villous length and decreased intestinal Oriol et al., 2009; De Jong et al., 2014). Regardless permeability. However, the effect of diet compos- if fed as mash or pellets, pigs prefer to consume ition on mucosal integrity was less important than diets manufactured with coarser (700 μm) ground the low energy intake observed in both treatment corn (Bokelman et al., 2015; Gebhardt et al., 2018). groups. Fermented liquid feeds is another strategy Furthermore, coarse ground mash diets may offer that may offer potential benefits by helping to de- GI benefits by lowering stomach pH and reducing crease stomach pH through lactic acid production, the incidence of pathogenic bacteria (Vukmirovic thereby inhibiting the growth of pathogenic organ- et  al., 2017). Similarly, research shows that young isms (Moran, 2001). However, Lawlor et al. (2002) pigs prefer pellets with a large diameter (12  mm) observed no added benefit from feeding weanling compared to smaller pellets (van den Brand et al., pigs a fresh liquid milk replacer or fermented liquid 2014). In fact, Clark et  al. (2015) observed that diet, as compared to a standard dry pelleted diet. feeding a large pellet immediately post-weaning In summary, due to low FI immediately increased FI, regardless of previous creep feed post-weaning, researchers often struggle to detect pellet size. In agreement with this data, others have Translate basic science to industry innovation Continuity of nutrient intake after weaning observed irrespective of pellet diameter provided oats having the highest preference during the nur- after weaning, pigs exposed to large creep pel- sery phase. Furthermore, the authors observed fish lets pre-weaning exhibit improved FI and growth meal, soybean meal and spray dried porcine blood post-weaning (van den Brand et  al., 2014). These plasma to have the highest preference of protein data suggest a relationship between diet form and sources which was, greater than that for dried skim particle size when offered both pre- and post-wean- milk. Specifically, dried porcine solubles has a large ing on preference and FI. mean particle size (Sola-Oriol et  al., 2009), which Palatability.  Young pigs are sensitive to palat- may explain the preference for this ingredient. While ability, which therefore drives consumption pref- palatability of feed ingredients should be taken into erences. Undoubtedly, odor and taste play an account when formulating diets for weanling pigs, it important role in palatability (Sola-Oriol et  al., is important to note that preference doesn’t always 2009). Nowicki et  al. (2015) observed that objects equate to higher FI, especially when pigs are not aromatized with moist soil, grass, and dried mush- given a choice between diets. rooms were more attractive to weanling pigs than Diet complexity.  Diet complexity in the im- synthetic aromas. This study did not investigate mediate post-weaning period can mean many dif- the effect of aroma preference on FI but does offer ferent things, including the addition of cooked potential opportunities for environmental enrich- or heat processed cereal grains, a variety of spe- ment strategies to improve exploratory behavior cialty protein products, and dried milk alternatives. and reduce weaning stress. Furthermore, adding Generally, feeding more complex diets during the flavor enhancers or sweeteners to starter diets im- first week post-weaning improves pig growth and mediately after weaning may encourage solid FI efficiency (Sulabo et al., 2010; Collins et al., 2017). (Torrallardona et al., 2001; Langendijk et al., 2007; However, the initial benefits of providing complex Sterk et  al., 2008). However, the literature is in- diets is quickly diminished as pigs become older. consistent, and data are largely dependent on the Four experiments conducted by Mahan et al. (2004) amount and flavor used, feeding duration, and at demonstrated that pigs had increased initial growth what point flavored feed was introduced to pigs. performance when fed complex diets with lactose Flavor imprinting is another strategy that could until 25 kg BW. Others have reported no improve- be used to reduce weaning stress and encourage FI ment in performance when complex diets were fed after weaning. Oostindjer et al (2010) observed that (Steidinger et al., 2002). Because complex diets are pigs exposed to flavors in the diet of the sow be- often more expensive, Collins et  al. (2017) inves- fore birth and during lactation, then subsequently tigated the economic impacts of diet complexity re-exposing to the same flavor at weaning had in- when fed to light, medium, and heavy weight pigs. creased FI and reduced incidence of stress-related The authors observed that feeding more complex behaviors. Figueroa et al. (2013) also observed that diets was only cost effective for light weight pigs brief contact with a demonstrator pig that recently (<6.5  kg), which was attributed to increased life- consumed flavored feed was enough to change the time performance. Douglas et  al. (2014) showed feeding behavior of naïve observers, enhancing that feeding a high-quality starter regime to the low their preference for flavored feed. These effects may birth weight population improved post-weaning pig be in response to reduced stress due to the pres- performance and increased profitability, whereas ence of a familiar flavor in the post weaning en- there was no effect of starter regime on the average vironment (Oostindjer et  al., 2010). As previously or heavy birth weight population. Similar improve- discussed, feed preferences are also influenced by ments have been observed with increasing lactose diet form and complexity. Sola-Oriol et  al. (2009) in diets for light weight pigs (Mahan et al., 2004). demonstrated that while particle size characteristics These data indicate that light weight pigs or those showed only marginal correlations with feed prefer- less developmentally mature may be better suited ence, the hardness, fragility, and time spent chewing for more complex starter diets. showed a statistically significant negative correl- It is well understood that starter diets are im- ation with FI. This supports the presumption that portant for providing glucose and other essential feed requiring a shorter chewing time may be pre- nutrients to the newly weaned pig. Regardless ferred in weanling pigs. In a series of experiments of composition though, the challenge becomes investigating a variety of common feed ingredients, getting pigs to actually consume feed following Sola-Oriol et al. (2014) determined that cereal grain weaning. Under normal circumstances when en- preference increased as digestible starch increased ergy intake is low, the hypothalamus senses dimin- and crude fiber decreased, with naked or refined ishing plasma glucose concentrations subsequently Translate basic science to industry innovation Wensley et al. inhibiting the mechanistic target of rapamycin acidity and improve weanling pig buffer capacity complex 1 signaling pathway (mTORC1; Takei (Ravindran and Kornegay, 1993). Likewise, re- et  al., 2014). Inhibition of mTORC1 is thought search has demonstrated that diet acidification to elicit an increase in FI (Wiczer and Thomas, helps improve protein digestibility (Ravindran and 2010). Unfortunately, this is often not the case in Kornegay, 1993). Similar to organic acids, the in- the immediate post-weaning period. As discussed clusion of whey or lactose in starter diets helps by Wensley et al. (2020), weaning associated stress lower gastric pH by ensuring continued lactic acid may impair normal hypothalamic activation. This production (Lawlor et al., 2005), thereby reducing suggests a complex relationship between stress the need for diet acidification (Partanen and Mroz, and energy homeostasis, which may impact the 1999). These responses are found to decrease with pig’s decision to consume feed. Amino acid levels, age as GI enzymatic activity develops (Yen, 2001). growth factors, and insulin signaling also regu- The improvement of weanling pig buffer capacity late mTORC1 activity, therefore playing a role in through a better understanding of feed ingredi- a multitude of cellular processes necessary for FI, ents is an area of research that still requires further and subsequent growth and survival (Takei et  al., investigation. 2014). Dietary fiber content is another feeding strategy Influence of diet complexity on GI maturation of interest. Providing insoluble fibers in the diet is and post-weaning diarrhea. Diet composition is cru- known to accelerate digesta passage rates and lower cial to the growth and development of the naïve intestinal bacterial adhesion, which increases fecal pig’s GI system, as well as reducing the occurrence DM, offering an opportunity to reduce post-wean- of post-weaning diarrhea. Soybean meal contains ing diarrhea (Montagne et  al., 2003). Conversely, anti-nutritional factors and allergenic proteins that providing soluble fibers in the diet slows digesta reduce nutrient utilization and lower growth per- passage, increasing the production of short-chain formance following first exposure (Li et al., 1990). fatty acids (SCFA). Specifically, butyrate is a SCFA These effects are often temporary with pigs devel- that can be used as a readily available source of en- oping tolerance after 1–2 weeks (Engle, 1994). ergy for a variety of GI functions (Blaut, 2002), Consequently, specialty animal proteins are fre- including regulation of epithelial cell growth (Liu quently added to nursery starter diets in place of et  al., 2018), and reduced intestinal inflammation soybean meal because they contain highly digest- (Liu, 2015). While data is limited, supplementing ible AA and are often more palatable than plant butyrate may be conditionally important in young protein sources. This helps alleviate the adverse pigs undergoing intestinal maturation while also ex- effects of soybean hypersensitivity by slowly accli- periencing weaning stress. Research evaluating the mating wean pigs to increasing levels of soybean effect of fiber sources often observe no performance meal in the diet. Furthermore, feeding low crude differences (Menegat et  al., 2019a). However, gut protein/AA fortified diets, allows nutritionists the health tends to be positively impacted, with a more opportunity to reduce intact protein sources while pronounced response observed when insoluble fi- concurrently increasing the use of highly digest- bers are fed immediately after weaning (Menegat ible crystalline AA (Wang et  al., 2018). For these et al., 2019a). reason, low crude protein diets have gained atten- Lastly, zinc is commonly added to nursery pig tion over the last decade because of their ability to diets at pharmacological levels to reduce post-wean- effectively lower post-weaning diarrhea (Heo et al., ing diarrhea and improve growth performance 2009). (Hill et  al., 2001). High levels of zinc have also Because suckling pigs are consuming high been shown to positively influence intestinal integ- levels of milk lactose, a precursor for lactic acid, rity and the immune system of weanling pigs (Liu stomach acidification by HCl is inhibited (Cranwell et al., 2018). While the mechanisms of pharmaco- et al., 1976). At weaning, consumption of solid feed logical levels of zinc are largely unknown, Ou et al. reduces lactic acid production, thereby stimulating (2007) observed that added zinc inhibited stem cell the production of HCl (Yen, 2001). This often leads factor gene expression, which are responsible for to an elevation in gastric pH resulting in reduced di- mast cell proliferation and subsequent histamine gestion of feed and a more favorable environment expression. Mast cell derived histamine has been for pathogenic bacteria, which may incite diarrhea linked to the pathogenesis of diarrhea, indicating (Lawlor et  al., 2005; Wang et  al., 2018). The add- one potential mode of action for added zinc (Ou ition of organic acids to starter diets is a well-recog- et  al., 2007). Copper is another important trace nized feeding strategy used to manipulate stomach mineral that offers improved fecal consistency and Translate basic science to industry innovation Continuity of nutrient intake after weaning growth promoting benefits when added at pharma- diets increased gut microbial diversity and decreased cological levels in nursery pig diets (Menegat et al., body lesions in pigs during immediate post-wean- 2019b). While it’s mode of action is also not well ing period (Parois et al., 2020). Furthermore, added defined, the growth promoting effects of copper L-glutamine resulted in decreased tear staining and have been attributed to its bacteriostatic and bac- greater interest in novel objects. An earlier report tericidal properties (Espinosa and Stein, 2021). showed that lying behavior in the first 2 d after Copper supplementation is also recognized to in- simulated transport was increased in groups that crease lipase activity, stimulate growth hormone se- did not receive antibiotics compared to antibiotic cretion, indirectly improve immune responses, and or L-glutamine fed pigs (Johnson and Lay, 2017). It increase mRNA genes involved in post-absorptive is well established in humans and rodents that mi- metabolism of lipids (Espinosa and Stein, 2021). crobial dysbiosis is associated with depressive and Feed ingredients that may impact GI health anxiety like behaviors (Kelly et  al., 2015), which and FI.  Gastrointestinal health around the time may explain the reduction in aggression, stress, and of weaning is often compromised as a result of fear related behaviors observed in pigs fed added stress and low FI. Fatty acids and other lipids in glutamine (Johnson and Lay, 2017; Parois et  al., sow’s milk are a highly digestible energy source 2020). Together, these data suggest that glutamine frequently not provided in the post-weaning diet has an interactive role on GI health, development, (Lauridsen, 2020). The strategic use of FA supple- and the microbiome-gut-brain axis. While these mentation may benefit the growth and development data suggest a positive response to glutamine when of the GI system through energy maintenance, es- fed in nursery starter diets, widespread adaptation pecially while under inflammatory conditions (Liu, of glutamine supplementation has not been seen. 2015). Trials conducted in rats and humans have Glutamine has not approved for feeding in all loca- demonstrated that diets enriched with omega-3 tions globally. polyunsaturated FA may help downregulate meta- Tryptophan (Trp) is an essential AA that acts bolic factors associated with glucose depletion and as a precursor for the neurotransmitter serotonin, GI inflammation (Barber et al., 1999; 2001; Huber which is associated with mood, sleep and appetite et al., 2018). Adding dietary FA post-weaning, may regulation (Le Floc’h and Seve, 2007). It is well provide opportunities to improve pig health and established that diets deficient in Trp reduce FI. increase nutrient utilization, particularly in health Furthermore, when pigs are exposed to inflamma- challenged systems. tory, immune or environmental stressors, serotonin Glutamine is a conditionally essential AA catabolism in the brain increases (Takeda et  al., that has been also been identified for its role in 2004). This mechanism is designed to help prevent GI function (Lewis, 2001). Specifically, glutamine mood disturbances and depressive disorders; how- is recognized as the primary energy source for in- ever, it may lead to a shortage of serotonin as ex- testinal enterocytes (Wu et  al., 1996). When sup- penditure exceeds synthesis (Takeda et  al., 2004). plemented in starter diets at 1%, L-glutamine has These effects may be intensified when FI is limited been shown to prevent jejunal atrophy during the (Le Floc’h and Seve, 2007). Supplemental Trp has first week postweaning (Wu et  al., 1996), increase been reported to reduce stress hormone concen- intestinal cell proliferation, and reduce the ex- trations, which may be beneficial in the immediate pression of genes associated with oxidative stress post-weaning period (Koopmans et  al., 2005; Liu (Wang et al., 2008). Similarly, others have demon- et al., 2013). Early research has indicated that Trp strated the importance of glutamine on tight junc- may also modulate plasma insulin secretion and tion protein regulation and CRF expression (Wang sensitivity (Cortamira et  al., 1991), suggesting a et  al., 2015). In support of these findings, earlier role in glucose metabolism. Increasing dietary Trp reports indicate that glutamine may become con- also induces high ghrelin levels along the GI tract ditionally essential in times of immune system ac- (Zhang et  al., 2007). Ghrelin is a 28-AA peptide tivation, particularly during stress when the body’s hormone secreted from the stomach that is involved glutamine requirement appears to exceed its rate of in the mTOR signaling pathway and is believed to production (Lacey and Wilmore, 1990). Duttlinger regulate FI in response to serotonin levels (Zhang et al. (2019) showed that after a 12 h transport, re- et al., 2007; Nørgaard et al., 2015). placing dietary antibiotics with 0.20% L-glutamine Sodium and chloride are also of particular improved pig performance and health during the importance for nursery pigs. These minerals, first 14 d after placement. Under similar transport commonly fed in the form of salt, are involved conditions, L-glutamine supplementation in starter in nutrient absorption, electrolyte balance, and Translate basic science to industry innovation Wensley et al. regulation of pH (Menegat et  al., 2019b). Diets • Liquid feeding/milk replacer: Liquid feeding that are deficient in salt result in decreased growth strategies do offer opportunities to increase DM performance due to reduced FI and poor feed ef- intake in the immediate post-weaning period, ficiency (Shawk et al., 2018a, b). For 5–7 kg wean- particularly in lightweight pigs. The implications ling pigs, providing 0.4% and 0.5% sodium and on death loss and culling rates need to be con- chloride, respectively is necessary to meet their sidered. Does offering liquid feed immediately requirement. after weaning require a second weaning period Enzymes are another area commonly studied, when pigs are transitioned from the liquid diet to with phytases contributing the greatest benefit. solid feed? While phytase is not known for increasing FI, it • Delayed feeding: Does delayed feeding offer an is well established that adding exogenous phytase opportunity for pigs to get acclimated with a new to swine diets helps improve phosphorus avail- environment and pen mates, prior to feed stim- ability. Compared to standard doses (<1,000 FTU), uli? Would the sound of feed being dropped into super-dosing phytase (<2,000 FTU) has been shown feeders encourage feed behavior? And how long to provide additional benefits beyond phosphorus of a delay is too long? release, which may be attributed to the release of • Diet form: Influence of crumble diets on pig inositol from the phytate complex. Moran et  al. feeding preference and growth performance, (2019) demonstrated that increasing exogenous compared to meal and pellet diets. inositol improved feed efficiency in pigs fed diets • Diet palatability: More research is needed on without phytase, equivalent to the improvement the concept of early flavor experiences. Does observed with super-dosing phytase. Following the perinatal or social interaction flavor learning in- immediate post-weaning period, FI increased as in- crease feed acceptance post-weaning as a result ositol supplementation increased in the absence of of flavor association? phytase. Though the mode of action is unknown, • Diet considerations: More research is still needed this suggests that inositol may be conditionally es- to determine the effect high fiber and low crude sential in diets of weanling pigs. Croze and Soulage protein, AA fortified diets on post-weaning diar - (2013) suggest that myo-inositol has a role in insulin rhea and growth performance. signaling and protein synthesis, possibly improving glucose metabolism and contributing to improved performance. CONCLUSION Weaning older, heavier pigs and encouraging Gaps in Knowledge feeding behavior through environmental and nu- Reducing nutrient disruption after weaning can tritional strategies will help improve FI and early be accomplished through further exploration of growth immediately after weaning. According to a multiple post-weaning strategies. Understanding study conducted by Pluske (2013), husbandry and the long-term implications of these strategies is also management techniques, including hygiene and crucial. education, offer the greatest potential for reducing nutrient disruption at the time of weaning. Several • Thermoneutral zone: What environmental tem- factors are known to influence nutrient intake after peratures are ideal, in accordance with season, weaning including: to encourage pen exploration and reduce latency to first feeding? • Feed availability: Easy access to feed improves • Feed availability: Mat and gruel feeding are com- immediate post-weaning FI. This is influenced monly practiced throughout the industry; how- by pen size, group size, feeder design, and loca- ever, limited data is available to document the tion of feeder relative to water. value of these feeding strategies. • Water quality: High levels of dissolved minerals • Water availability: More research in commercial in the water do not hinder performance but may settings with larger group sizes is needed to de- influence diarrhea scours and appearance of termine adequate water space. Additionally, how looseness. does wet/dry feeding impact water space require- • Water enrichment: Water enrichment strategies ments? And how does feeder arrangement rela- do provide additional nutrients that have been tive to drinker location affect FI and subsequent shown to benefit growth performance and mor - performance. bidity and mortality when FI is low. Translate basic science to industry innovation Continuity of nutrient intake after weaning patients with pancreatic cancer. Br. J.  Cancer 81:80–86. • Nursery placement: Sorting pigs into uniform doi:10.1038/sj.bjc.6690654 BW groups is beneficial for light weight pigs but Bergstrom,  J., and D.  McKilligan. 2006. An evaluation of li- not heavy weight pigs. quid feeding immediately post-weaning to improve the • Diet form: For young pigs the implication of diet performance of the lightest pigs within a nursery group. form on palatability preference is an important Allen D. Leman Swine Conference, Minneapolis, MN. Blaut,  M. 2002. Relationship of prebiotics and food intes- consideration. Pelleted diets increase feed effi- tinal microflora. Eur. J.  Nutr. 41:11–16. doi:10.1007/ ciency and nutrient digestibility compared to s00394-002-1102-7 meal diets. Regardless if fed as a meal or pellet Bokelman,  G.  E., J.  A.  De  Jong, J.  R.  Kalivoda, A.  Yoder, though, weanling pigs prefer diets manufactured C. R. Stark, J. C. Woodworth, and C. K. Jones. 2015. Finely with coarse (700  μm) ground corn rather than grinding cereal grains in pelleted diets offers little improve- fine ground corn. When pelleted diets are fed ment in nursery pig growth performance. Kansas Agric Exp Station Res Rep. 1:17. doi:10.4148/2378–5977.1122 however, young pigs prefer pellets with a larger van  den  Brand,  H., D.  Wamsteeker, M.  Oostindjer, diameter. L. C. M. van Enckevort, A. F. B. van der Poel, B. Kemp, and • Diet complexity: Feeding more complex diets J.  E.  Bolhuis. 2014. Effects of pellet diameter during and during the first week post-weaning improves pig after lactation on feed intake of piglets pre- and postwean- growth and efficiency, with the greatest response ing. J. Anim. Sci. 92:4145–4153. doi: 10.2527/jas2014-7408 Brooks, P. H., S. J. Russell, and J. L. Carpenter. 1984. Water in- observed in the lightweight pig population. The take of weaned piglets from three to seven weeks old. Vet. initial benefits observed in performance tend to Rec. 115:513–515. doi:10.1136/vr.115.20.513 decrease with increasing time post-weaning. Brooks,  P.  H., and C.  H.  Tsourgiannis. 2003. Factors af- • Diet palatability: Young pigs are sensitive to pal- fecting the voluntary feed intake of the weaned pig. atability which is influenced by odor, taste, and In: J.  Le  Dividich, J.  R.  Pluske, M.  W.  A.  Verstegen, texture. Therefore, feed ingredients should be editor, Weaning the Pig: Concepts and Consequences. Wageningen, Netherlands: Wageningen Academic taken into account when formulating diets for Publishers. p. 81–116. newly weaned pigs. Increased preference doesn’t Bruininx,  E.  M.  A.  M., C.  M.  C.  van  der  Peet-Schwering, always equate to higher FI, especially when pigs J. W. Schrama, P. F. G. Vereijken, P. C. Vesseur, H. Everts, are not given a choice between diets. L.  A.  den  Hartog, and A.  C.  Beynen. 2001. Individually • Diet ingredients and nutrients: Organic acid supple- measured feed intake characteristics and growth perform- ance of group-housed weanling pigs: effects of sex, initial mentation, crude protein level, insoluble fiber in- body weight, and bodyweight distribution within groups. clusion, and zinc and copper concentrations alter J. Anim. Sci. 79:301–308. doi: 10.2527/2001.792301x the occurrence of post-weaning diarrhea. Fatty ac- Carey, H. V., U. L. Hayden, and K. E. Tucker. 1994. Fasting al- ids and functional AA such as glutamine and Trp ters basal and stimulated ion transport in piglet jejunum. positively influence gut health and subsequent FI. Am. J.  Physiol. 267(1 Pt 2):R156–R163. doi:10.1152/ Salt concentrations also play an important role in ajpregu.1994.267.1.R156 Clark, A. B., J. A. De Jong, J. M. DeRouchey, M. D. Tokach, FI and palatability preferences, with myo-inositol S. S. Dritz, R. D. Goodband, and J. C. Woodworth. 2015. having more recent implications on FI. Effects of creep feed pellet diameter on suckling and nur- sery pig performance. Kansas Agric Exp Station Res Rep. ACKNOWLEDGMENTS 8:13. doi:10.4148/2378–5977.1118 Collins, C. L., J. R. Pluske, R. S. Morrison, T. N. McDonald, Contribution no.  21-114-J from the Kansas R. J. Smits, D. J. Henman, I. Stensland, and F. R. Dunshea. Agricultural Experiment Station, Manhattan, 2017. Post-weaning and whole-of-life performance of pigs 66506-0201. Appreciation is expressed to TechMix is determined by live weight at weaning and the com- plexity of the diet fed after weaning. Anim. 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Journal

Translational Animal ScienceOxford University Press

Published: Feb 8, 2021

Keywords: feed intake; nutrient disruption; pig; post-weaning

References