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In situ rumen degradation of kernels from short-season corn silage hybrids as affected by processing,

In situ rumen degradation of kernels from short-season corn silage hybrids as affected by... Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of kernels from short-season corn silage hybrids as 1,2 affected by processing ,† † ‡ †,3 Renan L. Miorin,* Lucia Holtshausen, Vern Baron, and Karen A. Beauchemin *Departamento de Zootecnia, Universidade Estadual de São Paulo, Jaboticabal, SP, Brazil; Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB T1J 4B1, Canada; and Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, Lacombe, AB T4L 1W1, Canada ABSTRACT: The objective of this in situ study Differences in digestion kinetics among hybrids was to evaluate the rumen degradability of ker- were generally more pronounced for starch than nels from short-season corn hybrids grown for DM. The hybrids differed in starch degradability silage in Western Canada (Lacombe, AB) and (P  <  0.05), with earlier maturing hybrids having determine whether decreasing kernel particle lower A  fraction, lower k , and lower ED, with size would enhance ruminal degradability in a hybrid effects on ED being accentuated with faster similar manner for all hybrids. The study was a passage rate. Kernel DM content (r  =  −0.85, completely randomized design with 3 beef cows −0.87), hardness (r = −0.89, −0.86), and density (replicates) and a 6 (hybrid) × 3 (particle size) (r = −0.84, −0.85) were negatively correlated with factorial arrangement of treatments. Kernels ED4 and ED8 of starch, respectively, due mainly were processed to generate three different parti- to decreased k of fraction B. Reducing the par- cle sizes: large (2.3 mm), medium (1.4 mm), and ticle size of kernels increased ED of starch due small (0.7  mm). Processed samples were incu- to increased A fraction and k of the B fraction. bated in the rumen for 0, 3, 6, 12, 24, and 48  h A  tendency (P  =  0.09) for hybrid × processing using the in situ method and degradation kinet- effects for ED6 and ED8 indicated that process- ics of DM and starch were determined. Effective ing had greater effects on increasing ED of starch rumen degradability (ED) was estimated using for earlier maturing hybrids. We conclude that a passage rate of 0.04 (ED4), 0.06 (ED6), and short-season hybrids that mature early may have 0.08/h (ED8). Hybrids exhibited a range in whole lower ED of DM and starch and would benefit plant DM content (23.7 to 25.0%), starch con- from prolonged ensilage time. Kernel process- tent (15.9 to 28.1% DM), kernel hardness (21.9 to ing during silage making is recommended for 34.4 s/20 g) and density (3.57 to 4.18 g/mL), and short-season corn hybrids as a means of enhanc- prolamin content (8.24 to 11.34  g/100  g starch). ing rumen availability of starch. Key words: corn heat unit, corn silage, degradability, grain processing, starch © Crown copyright 2018. Transl. Anim. Sci. 2018.2:428–438 doi: 10.1093/tas/txy084 INTRODUCTION This study was conducted with financial sup - Corn silage is used extensively in cattle diets port from the Beef Cattle Research Council worldwide. Development of corn hybrids that (Canada) and Agriculture and Agri-Food Canada. require a short growing season together with Lethbridge Research and Development Centre contribu- changes in climate have led to increased corn tion number: 38718023. 3 silage acreages in areas with colder climates such Corresponding author: karen.beauchemin@agr.gc.ca as parts of Canada, Asia, and Northern Europe Received June 11, 2018. Accepted July 3, 2018. (Ramirez-Cabral et al., 2017). Corn silage can be 428 Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 429 a good alternative to other forages for beef and Development Centre Animal Care Committee in dairy cattle because of its high DM yield and compliance with the guidelines of the Canadian high total digestible nutrient content [National Council on Animal Care (1993). Academies of Sciences, Engineering, and Medicine (NASEM), 2016]. Corn Hybrids and Kernel Preparation Corn hybrids marketed in Canada are rated for Six short-season corn hybrids (H1 to H6) were maturity using the corn heat unit (CHU) system grown in 2015 at Lacombe, AB (latitude: 52°28′N; (Brown and Bootsma, 1993). This rating indicates longitude, 113°45′W), an area with fine sandy loam the number of accumulated thermal units needed soil and Orthic black soil classification. Lacombe for corn to reach maturity. Areas within Canada has a long-term CHU rating of 1800 to 2000. are mapped according to long-term weather data During the study year, 1,837 CHU accumulated and hybrids are then selected such that their CHU between seeding and harvest; thus, the year was rating fits within the CHU rating of the location in relatively cool but within the long-term average for which they are grown. Short-season corn hybrids the location (Table  1). The hybrids were selected are of flint and dent genetic populations, with flint to provide a range in CHU ratings suitable for the heritage used to confer early silking dates, cool tem- area (2,000 to 2,200 CHU). Hybrids H1 (7632HR, perature and drought tolerance, and resistance to 2,200 CHU), H4 (39M26, 2,100 CHU), H5 (7213R, kernel damage during combining (Unterseer et al., 2,050 CHU), and H6 (39F44, 2,000 CHU) were 2016). obtained from Pioneer Hi-Bred (Johnston, IA), Corn grain has a protein matrix in its endo- whereas H3 (Edge, 2,015 CHU) was from Elite sperm that protects the starch granules. Hybrids (Saint-Hyacinthe, QC) and H2 (2262RR, 2,175 of flint origin have greater proportion of vitreous CHU) from Pickseed (Lindsay, ON). The hybrids endosperm in the kernel making the starch harder were seeded (average plot size of 11.0 m ) on May to degrade because it is protected by a thick pro- 5 (74,000 seeds/ha and row spacing 75  cm using tein matrix that hinders access of ruminal bac- two-row corn planter, John Deere), The corn was teria to the site of digestion (Szasz et  al., 2007; not irrigated but received 278.6  mm of precipita- Hoffman and Shaver, 2009; Rossi et al., 2016). In tion during the growing season. Inorganic fertil- contrast, hybrids of dent origin have greater pro- izer was applied to the plots to supply 212 kg/ha N, portion of floury endosperm and thus have more 60 kg/ha P, and 72 kg/ha K. The hybrids were har- digestible starch because the granules are loosely vested on September 15 because frost was forecasted packed and the surrounding protein matrix is thin- to occur later in the week (minimum temperature ner (Hoffman and Shaver, 2009; Rossi et al., 2016). was −2.0 °C and −0.2 °C on September 17 and 18, It is uncertain whether starch degradability of 2015, respectively). short-season corn hybrids grown for silage is lim- At harvest, five ears from each hybrid were col - ited by genetic origin, and whether extensive pro- lected, frozen (−20 °C), and shipped to Lethbridge, cessing is needed to maximize rumen availability. AB. The remaining plants were harvested and a Kernel processing during harvesting for silage can 5-kg representative sample was dried at 55 °C to a minimize the effects of kernel hardness and vitre- constant weight and used to determine whole plant ousness on starch digestibility; thus, it is possible starch and NDF contents. Silk and husks were that starch degradability of short-season hybrids could be increased by more extensive processing (Philippeau et al., 1999; Andrae et al., 2001; Szasz Table  1. Corn heat unit (CHU) rating and whole et al., 2007). plant nutrient and physical composition of corn The objective of this in situ study was to evalu- hybrids grown at Lacombe, AB, Canada in 2015 ate the degradability of kernels from short-season Hybrids CHU DM, % CP, % DM Starch, % DM NDF, % DM corn hybrids grown for silage in Western Canada H1 2,200 23.7 8.02 15.9 54.4 (Lacombe, AB) and determine whether process- H2 2,175 24.9 8.21 16.4 53.9 ing to decrease particle size would enhance kernel H3 2,150 25.7 8.04 18.2 53.3 degradability. H4 2,100 23.7 8.09 21.8 51.1 H5 2,050 24.2 8.34 19.7 54.1 H6 2,000 25.0 8.31 28.1 50.5 MATERIALS AND METHODS Accumulated CHU, calculated starting from the day following three Animal handling and care procedures were consecutive days after seeding with mean daily temperature ≥12.8 °C approved by the Lethbridge Research and until harvest, were 1,837 at Lacombe, AB, in 2015. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 430 Miorin et al. removed from the cobs, frozen cobs were broken in required to produce 17  mL of flour when a 20-g half, and 10 kernels were removed from the edge of sample of air-dried kernels is passed through a cut- each half and dried at 55 °C to a constant weight ter mill (Retsch GmbH, Haan, Germany) equipped to determine DM content of kernels. The cobs were with a 2-mm screen. Density was measured as the then air-dried in a temperature controlled, well ven- weight of the ground sample (g/mL). tilated room until dry. Kernels were removed from Mean size by mass (mm) of the processed ker- the cobs using a lab-scale sheller and retained for nels used in the in situ study was determined using the study. a sieve shaker (Ro-Tap, W.S. Tyler, Mentor, OH) equipped with eight sieves arranged in descending order (4.75, 2.36, 1.18, 0.6, 0.425, 0.3, 0.212, and Treatments 0.096  mm) above a collection pan. A  subsample The study was a completely randomized design (100  g) of air-dried kernels from each processed with 3 beef cows (replicates) and a 6 (hybrid) × 3 hybrid was placed on the top sieve and shaken con- (particle size) factorial arrangement of treatments. tinuously for 10  min. Weight over size generated The kernels from each hybrid were processed to during this procedure was used to compute the generate three different particle sizes (Table  2): geometric mean diameter size and standard devi- large (cracked with hammer), medium (chopped ation (SD ), according the ASABE Standard gmd using a Ninja blender, SharkNinja Co., Champlain, (2008) methodology. The assumption is that par- NY), and small (ground through a 2-mm screen, ticle size of ground feeds is logarithmic-normally standard model 4 Wiley Mill, Arthur Thomas Co., distributed. Philadelphia, PA). Geometric mean diameter (mm) was calculated as follows: Physical Measurements   (l Wi og di ) −1   Geometricmeandiametersizel = og Kernel hardness (Table  3) of whole kernels   Wi   was determined using the Stenvert test (Blandino et al., 2010), which measured the time (in seconds) where Wi = weight (g) on the ith sieve. Table  2. Geometric mean diameter size (GMD, In Situ Measurements mm) and standard deviation (SD ) of processed gmd Ruminal degradation of DM and starch was kernels from short-season corn silage hybrids grown determined using the in situ method as adapted by in Lacombe, AB, Canada Griffith et  al. (2017) . Three mature, ruminally can- Size nulated beef cows (mean ± SD; 650  ±  30  kg BW) Large Medium Small were offered for ad libitum intake a diet consisting GMD, mm SD GMD, mm SD GMD, mm SD Hybrid gmd gmd gmd of 19% barley grain, 62% corn silage, 13% corn dis- H1 2.39 0.29 1.29 0.28 0.68 0.19 tillers dried grains, and 6% vitamin/mineral supple- H2 2.19 0.29 1.40 0.29 0.71 0.20 ment (DM basis). Approximately 6 g of each hybrid H3 2.22 0.29 1.36 0.28 0.74 0.20 sample was weighed in duplicate into 10  ×  18  cm H4 2.21 0.28 1.36 0.30 0.71 0.22 polyester bags (R1020, ANKOM Technology, H5 2.38 0.28 1.59 0.30 0.69 0.21 Macedon, NY; 50-μm porosity). The bags were H6 2.41 0.27 1.48 0.30 0.74 0.21 sealed, placed inside larger mesh bags (30 × 30 cm) Log-normal SD. with three equal-sized channels sewn into them to Table  3. Nutrient and physical composition of the corn hybrid kernels during the growing season at Lacombe, AB, Canada in 2015 Hybrid DM, % DM Starch, % DM Hardness, s/20 g Density, g/mL Prolamin, g/100 g starch H1 35.8 60.4 21.9 3.57 8.24 H2 37.3 59.0 23.2 3.70 10.01 H3 39.9 57.6 24.9 3.86 8.29 H4 45.8 56.4 24.9 4.04 11.34 H5 43.8 60.0 28.2 3.81 10.22 H6 49.7 58.2 34.4 4.18 10.51 Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 431 keep the smaller polyester bags from aggregating 2005) by drying samples at 135 °C for 2 h, followed together. Three polyester bags were placed in both by hot weighing. The original kernels and bag outside channels of the larger mesh bags, and two residues were ground using a ball grinder (Mixer were placed in the middle channel of the mesh bags. Mill MM2000; Retsch, Haan, Germany) prior to There were a total of eight polyester bags per mesh determination of starch content in duplicate by bag and one mesh bag per time point. All bags were enzymatic hydrolysis of α-linked glucose polymers inserted in the rumen at 0900, just before the morn- as described by Chung et  al. (2011). The original ing meal. The bags were removed following 3, 6, 12, ground kernel samples were also used to determine 24, and 48 h of ruminal incubation. After removal, prolamin content in duplicate as described by Nellis bags were rinsed in cold water with ice and washed et al. (2013). For analysis of the whole plant mate- in cold water until clean. To estimate the soluble and rial, the dried samples were ground through a 1-mm washout fraction, 0-h bags were not inserted into the screen (standard model 4 Wiley Mill) and analyzed rumen, but were washed following the same process in duplicate for analytical DM content (method as previously described. Cows were the replicates, 930.15; AOAC, 2005), NDF (Ankom 200 system, such that for each incubation time 54 bags were incu- ANKOM Technology, Fairport, NY; heat-stable bated (6 hybrids × 3 particle sizes × 3 cows), total- α-amylase and sodium sulfite used in the assay), ing 324 bags (54 bags × 6 times) for the study. Bags and starch content as previously described. and residues were dried in a 55  °C forced-air oven for a minimum of 48 h. Dried bags with residue were Statistical Analysis weighed to determine DM disappearance (DMD). If Data for digestion kinetics were analyzed with the coefficient of variation was >10%, the bags were the MIXED procedure of SAS 9.2. The model reweighed or the outlier duplicate bag was discarded. included fixed effects of hybrid, particle size, The residues from each bag were analyzed for starch and their interaction, and cow as random effect. content to determine starch disappearance. Correlations were calculated using the CORR pro- The degradation kinetics of each hybrid and cedure of SAS 9.2. Means were declared signifi - treatment were calculated using the NLIN proce- cantly different when P < 0.05. dure in SAS program. Dry matter and starch dis- appearance values for the individual bags at each RESULTS time point were fitted to an exponential model: −kt Disappearance () tA =+ B () 1 − e Characterization of the Hybrids and Kernels where A  =  rapidly degradable fraction and wash- It was not possible to statistically evaluate out fraction (%); B  =  potentially degradable frac- −1 hybrid differences in chemical composition because tion (%); k  = degradation constant rate (h ), and there was only one field replication of each hybrid. t = incubation time (h). The hybrids ranged minimally in DM content from Effective ruminal degradability (ED) of DM 23.7% to 25.7%, yet starch content varied widely and starch was calculated according to equation: from 15.9 to 28.1% DM (Table  1). The CP (8.02   k to 8.34% DM) and NDF (50.5 to 54.4% DM) con- ED =+ AB   tents also varied minimally. The geometric mean kk +   dp diameter size and S of kernels from the hybrids gmd where k was the fractional ruminal passage rate after processing indicated that large, medium, and −1 (h ), which was assumed to be 0.04 (ED4), 0.06 small particles were obtained as planned (Table 2). (ED6), and 0.08 (ED8). The DM content of kernels at harvest varied from 35.8% to 49.7%, whereas starch content varied min- imally from 56.4 to 60.4% DM (Table  3). Kernel Chemical Analysis hardness varied from 21.9 to 34.4  s/20  g, density Whole kernels were weighed fresh and then ranged from 3.57 to 4.18 g/mL, and prolamin con- dried in a forced-air oven to a constant weight for tent ranged from 8.24 to 11.34 g/100 g of starch. the determination of kernel dry weight. Dried ker- nels were ground through a 2-mm screen (stand- DM and Starch Disappearance ard model 4 Wiley Mill; Arthur Thomas Co., Philadelphia, PA) and analyzed in duplicate for Differences among hybrids for DMD occurred analytical DM content (method 930.15; AOAC, at 0, 3, 6, and 24 h (P < 0.001; Table 4). Between 0 Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 432 Miorin et al. Table  4. Influence of hybrid and particle size Table  5. Influence of hybrid and particle size on on ruminal DM disappearance for kernels from ruminal starch disappearance for kernels from short-season corn hybrids grown in Lacombe, AB, short-season corn hybrids grown in Lacombe, AB, Canada Canada Incubation time, h Time (h) 0 3 6 12 24 48 0 3 6 12 24 48 Hybrid Hybrids a a a a b a ab a a a H1 25.6 43.6 52.0 55.7 83.5 92.3 H1 13.5 39.3 46.4 53.6 89.6 96.5 ab ab a a a a a a ab a H2 24.6 42.0 52.6 51.7 82.5 90.5 H2 20.4 40.9 50.8 52.7 88.7 97.6 b bc b a a b b a ab a H3 23.9 40.0 48.0 47.8 80.1 92.6 H3 19.8 32.2 42.4 44.9 83.8 95.9 c abc b a b b c a b ab H4 21.5 41.2 47.9 51.3 79.1 89.5 H4 13.5 31.8 35.1 50.6 82.2 93.2 c c b a ab b b a ab a H5 20.9 39.1 48.4 50.0 82.0 90.2 H5 15.3 31.0 44.6 46.8 85.7 94.0 d d c b b c d b c b H6 19.7 33.1 41.4 42.9 68.3 85.9 H6 13.4 21.7 29.1 31.4 64.2 87.9 SEM 0.67 2.70 2.70 6.05 4.76 4.57 SEM 3.04 4.42 3.88 7.38 5.23 4.02 Size Size c c c c b c c b b b Large 18.4 33.8 43.9 45.8 73.0 84.4 Large 10.9 25.5 36.8 42.4 74.7 87.8 b b b b a b b b b a Medium 21.7 40.2 47.4 50.4 78.1 91.3 Medium 16.3 33.3 37.5 47.0 79.3 95.9 a a a a a a a a a a Small 28.0 45.5 53.8 53.5 86.6 94.9 Small 20.7 39.7 49.9 50.6 93.1 98.8 P-value P-value Hybrid <0.001 <0.001 <0.001 0.160 <0.001 0.173 Hybrid 0.018 <0.001 <0.001 <0.001 <0.001 0.017 Size <0.001 <0.001 <0.001 0.088 <0.001 <0.001 Size <0.001 <0.001 <0.001 0.151 <0.001 <0.001 Hybrid × size 0.289 0.920 0.005 0.951 0.568 0.470 Hybrid × size 0.019 0.751 0.006 0.653 0.199 0.419 a–d a–d Means in the same column within hybrid and size categories with- Means in the same column within hybrid and size categories with- out a common subscript letter differ at P < 0.05. out a common subscript letter differ at P < 0.05. and 24 h of incubation (except 12 h), DMD of H6 degradable fraction (B) (P ≥ 0.179), with no interac- was clearly less than that of other hybrids (P < 0.05), tions (P ≥ 0.417) between hybrid and size (Table 6). but after 48 h of incubation hybrid differences were The soluble fraction A  was greater (P  <  0.05) for minimal (P = 0.173). Particle size influenced DMD H1 and H2 compared with the others, with hybrid at all incubation times (P < 0.001, except P = 0.088 H6 having the lowest soluble fraction, although at 12  h), with clear differences among the three not statistically different from H5 (P > 0.05). The particle sizes until 24 h. After 48 h, large particles rate of degradation (k ) (P  <  0.05) was lower for had lower DMD than the other particles (P ≤ 0.05), H6 compared with all other hybrids. Differences with no difference (P > 0.05) between medium and among hybrids for ED depended upon the rumen small particles. passage rate. With a slow passage rate, hybrid H6 Differences among hybrids (P ≤ 0.017) for had lower ED4 than the others (P < 0.05). With a starch disappearance occurred at all incubation medium passage rate, H6 had lower ED6 than the times (Table  5, Figures  1 and 2). Disappearance others (P < 0.05), but H4 also ranked lower than H2 of starch was always lower for H6 than for other (P < 0.05). For ED8, H6 remained lower than the hybrids (P  <  0.05), except at 0  h when it differed others (P < 0.05), but H3 and H4 also ranked lower only from H2 and H3 and at 48 h when it did not than H2 (P < 0.05). Thus, ED of DM was positively differ from H4. Particle size influenced starch dis - associated with CHU rating of the hybrid, and dif- appearance at almost all incubation times (Table 5, ferences in the degradability of hybrids increased as Figure 3). For the short incubation times of 0 and passage rate increased. The A fraction, ED4, ED6, 3 h the three sizes differed (P < 0.05), at 6 and 24 h and ED8 differed for large, medium, and small par- large and medium particles differed from small par- ticles (P  <  0.05), whereas k was similar for large ticles (P < 0.05), and at 48 h small and medium were and medium particles, but 33% greater for small similar but differed from large particles (P < 0.05). particles (P < 0.05). DM Degradation Kinetics Starch Degradation Kinetics The kinetics of DM degradation showed sig- For the kinetics of starch degradation (Table 7), nificant differences ( P  <  0.001) due to hybrid and significant ( P < 0.001) hybrid and particle size effects particle size for all variables except the potentially were observed for all variables (except size effect for Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 433 Figure  1. Influence of short-season corn hybrid and particle size on ruminal starch disappearance from kernels.  Symbols indicate observed values, while lines indicate predicted values based on Table 7. fraction B, P  =  0.122), and there was a tendency hybrids, H6 was consistently lowest, and the others for an interaction for ED6 (P  =  0.099) and ED8 were intermediate (P < 0.05). Hybrid H4 had lower (P = 0.070). Fraction A (P < 0.05) was greater for H2 ED (P < 0.05) than the other intermediate hybrids, compared with the other hybrids, with H4 and H6 when the passage rate was faster (ED6 and ED8). being lowest. The potentially degradable B fraction Thus, earlier maturing hybrids had lower A fraction, was lowest for H2, and greatest for H1, H4, and H6 lower k , and lower ED, with hybrid effects on ED (P < 0.05). For k , H6 was lower (P < 0.05) than all being accentuated with faster passage rate. others, which were similar. For ED (ED4, ED6, and Decreasing the particle size of the incubated ED8), H2 was consistently greater than the other material increased ED (P < 0.001), regardless of Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 434 Miorin et al. Figure 2. Influence of short-season corn hybrid on ruminal starch disappearance from kernels. Symbols indicate observed values, whereas lines indicate predicted values based on Table 7. Figure 3. Influence of particle size of kernels (large, medium, small) on ruminal starch disappearance for short-season corn hybrids. Symbols indicate observed values, whereas lines indicate predicted values based on Table 7. passage rate, mainly due to an increase in fraction small and medium sized particles on disappear- A and an increase in k for small vs. medium and ance were less for the later maturing hybrids. large particles (Table 7). The tendency for interac- tion between hybrid and size for ED6 (P = 0.099) Correlations and ED8 (P = 0.070) indicates that with a faster rate of passage, the effects of particle size reduc- There were positive correlations between tion on ED tended to differ among hybrids. The kernel DM content and hardness and density of interaction effects between hybrid and size on kernels (Table  8), and these characteristics were starch disappearance (observed and predicted) is negatively correlated with CHU rating of the shown in Figure  1. Processing the kernels had a hybrid, ED4 and ED8. As hardness and density much greater effect on starch disappearance of increased, k of starch degradation decreased. the earlier maturing hybrids (H3, H4, H5, and There was also a significant negative correlation H6) than for the later maturing hybrids (H1, between the A and B fractions (P < 0.01), where H2). Furthermore, the earlier maturing hybrids hybrids with a greater A fraction had less B frac- required fine processing to maximize starch dis - tion. In addition, there were positive correlations appearance, whereas the differences between between A, ED4, and ED8, where hybrids with Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 435 Table  6. Influence of hybrid and particle size Table  7. Influence of hybrids and particle sizes on ruminal DM disappearance for kernels from on ruminal starch disappearance for kernels from short-season corn hybrids grown in Lacombe, AB, short-season corn hybrids grown in Lacombe, AB, Canada Canada Item Item 1 2 3 −1 4 5 6 2 3 4 −1 5 6 7 A, % B, % k , h ED4, % ED6, % ED8, % A, % B, % k , h ED4, % ED6, % ED8, % d d 1 1 Hybrids Hybrids a a a ab ab bc ab a b b b H1 27.5 67.9 0.065 69.2 62.5 57.7 H1 15.8 83.1 0.069 67.9 59.8 53.9 a a a a a a c a a a a H2 27.0 68.6 0.069 69.8 63.1 58.2 H2 24.2 74.9 0.071 71.4 64.1 58.8 ab a a ab b b b a bc b b H3 25.4 71.4 0.063 67.8 60.8 55.8 H3 17.2 81.4 0.068 66.9 59.0 53.3 bc a a b b cd a a c c c H4 24.2 71.2 0.064 67.5 60.4 55.4 H4 11.1 88.4 0.062 64.1 55.3 49.1 cd a a ab ab bc b a bc b b H5 22.7 71.7 0.074 68.5 61.6 56.5 H5 15.1 81.5 0.072 66.8 58.9 53.2 d b b c c d ab b d d d H6 21.5 73.8 0.043 58.3 51.1 46.3 H6 9.88 87.5 0.042 53.1 44.7 39.1 SEM 1.30 3.85 0.007 2.36 2.20 2.05 SEM 2.84 3.84 0.008 2.91 2.89 2.82 Size Size c b c c c c b c c c Large 20.5 71.7 0.055 61.4 54.0 49.0 Large 11.1 84.9 0.052 58.4 49.9 44.1 b b b b b b b b b b Medium 24.5 71.9 0.058 66.2 59.3 54.2 Medium 16.0 83.2 0.058 64.1 55.9 50.1 a a a a a a a a a a Small 29.0 68.6 0.075 73.1 66.5 61.7 Small 19.6 80.3 0.082 72.7 65.1 59.5 P-values P-values Hybrid <0.001 0.316 <0.001 <0.001 <0.001 <0.001 Hybrid <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Size <0.001 0.179 <0.001 <0.001 <0.001 <0.001 Size <0.001 0.122 <0.001 <0.001 <0.001 <0.001 Hybrid × size 0.705 0.786 0.496 0.640 0.521 0.417 Hybrid × size 0.159 0.703 0.305 0.139 0.099 0.070 a–d a–d Means in the same column within hybrid and size categories with- Means in the same column within hybrid and size categories with- out a common subscript letter differ at P < 0.05. out a common subscript letter differ at P < 0.05. 1 1 Rapidly degradable fraction (%). Hybrids grown at Lacombe, AB, were within 2,000–2,200 CHU. 2 2 Slowly degradable fraction (%). Rapidly degradable fraction, %. 3 −1 3 Degradation rate constant (h ) of fraction B. Slowly degradable fraction, %. 4 4 −1 Effective degradability (%) with fractional passage rate of 0.04/h. Degradation constant rate, h . 5 5 Effective degradability (%) with fractional passage rate of 0.06/h. Effective degradability, with fractional passage rate of 4.0%/h. 6 6 Effective degradability (%) with fractional passage rate of 0.08/h. Effective degradability, with fractional passage rate of 6.0%/h. Effective degradability, with fractional passage rate of 8.0%/h. greater fraction A were more degradable. In con- trast, fraction B showed an inverse correlation Thus, this study aims to show potential differ- with ED. ences among hybrids adapted to a given location, rather than provide specific information for indi - DISCUSSION vidual hybrids. The corn hybrids used in the study were not ensiled; thus, the results indicate the effects of hybrid and particle size on ruminal degradation Characterization of the Hybrids and Kernels without the confounding effects of ensiling. The ensilage process would be expected to further The CHU ratings of the hybrids (Table  2) to increase ruminal starch degradability by 8 to 10 per- reach grain maturity exceeded the CHU received centage points after 3 mo in the silo (Der Bedrosian during the growing season. This is typical practice et  al., 2012; Windle et  al., 2014). Although whole for short-season growing areas as corn hybrids with plant corn is typically ensiled prior to feeding, in <2000 CHU rating are not commercially available. some cases, silage is fed prior to the optimum ensil- Because of the cool climate of this region, corn is ing duration because of limited feed supply (Heguy grown for silage rather than grain. In some years, et al., 2016). Furthermore, there is increasing use of the DM content at the end of the growing season direct grazed and swathed grazed whole plant corn is below the minimum recommended level of 30% for ensilage (Mahanna and Chase, 2003) especially for beef cattle (Baron et al., 2014b). for hybrids with greater CHU ratings. Because of The hybrids were grown in a single year and low temperatures and risk of frost, it is not possi- location. It is well known that maturity at har- ble to extend the growing season to increase matu- vest and chemical composition of a hybrid can rity at harvest. Such was the case in the present vary due to environmental growing conditions. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 436 Miorin et al. Table 8. Pearson correlation coefficients among variables for kernel characteristics and degradation kinet - −1 ics of starch with effective degradability estimated using a fractional passage rate of 0.04 h (ED4) and −1 0.08 h (ED8) Item Hardness Density CHU Starch Prolamin A B k ED4 ED8 DM 0.87* 0.94** −0.95** −0.49 0.72 −0.79 0.72 −0.77 −0.85* −0.87* Hardness 0.80* −0.94** −0.15 0.45 −0.61 0.48 −0.81* −0.89** −0.86* Density −0.83* −0.70 0.65 −0.71 0.69 −0.82* −0.84* −0.85* CHU 0.22 −0.63 −0.69 −0.55 0.69 0.81* 0.80* Starch −0.46 0.36 −0.47 0.38 0.31 0.36 Prolamin −0.38 0.37 −0.39 −0.38 −0.40 A,% −0.97** 0.69 0.80* 0.86* B,% −0.67 −0.75 −0.81* −1 k , h 0.96** 0.95** ED4, % 0.99** *P < 0.05. **P < 0.01. study where whole plant DM averaged (mean ± Greater differentiation in degradability kinet- SD) 24.5  ±  0.80%. The range in starch content of ics among the hybrids occurred when ED was the whole plant material from 15.9 to 28.1% DM estimated using a faster passage rate (i.e., ED8 vs. indicated that kernel filling was incomplete, espe - ED4), indicating that hybrid effects may be more cially for the hybrids that required greater CHU for important for dairy cows vs. feedlot cattle. Due maturity. The NDF content in corn silage declines as to faster rate of passage of feed from the rumen plants mature due to the dilution effect of increasing in dairy cows, proportionally less total tract diges- starch content (Hatew et  al., 2016); thus, the rela- tion of starch occurs in the rumen of dairy cows tively high NDF content of the whole plant hybrids compared with feedlot cattle (NASEM, 2016). (50.5 to 54.4% DM) is consistent with the low starch Shifting starch digestion from the rumen to the contents. In comparison, NASEM (2016) reported small intestine can decrease the risk of acidosis average values for corn silage grown in the United and improve the efficiency of energy yield if small States of (mean ± SD, DM basis) 33.1 ± 5.6% DM, intestinal digestibility is high (>75%) (Huntington 32.6 ± 7.0% starch, and 43.0 ± 5.5% NDF. The DM et al., 2006). However, small intestinal digestibility content of the kernels ranged from 35.8% to 49.7%, is typically only high when animals are fed at low which is consistent with the relatively immature stage intakes or when grains are highly processed; thus, of development of the hybrids at harvest. Although total tract digestibility may be reduced in dairy kernel stage of development was not measured in the cows fed short-season corn hybrids with low CHU present study, based on kernel DM content, it was rating. Furthermore, in vivo evaluations are needed probably close to early dough (Wiersma et al., 1993). to validate this hypothesis. Decreasing the particle size of the kernels increased availability of the DM and starch in the DM and Starch Degradation rumen by increasing the A fraction and k of the B fraction. Increased A fraction indicates greater Generally, differences in digestion kinetics washout and solubility occurred with smaller among hybrids were more pronounced for starch particle size, whereas increased k indicates that than for DM. The kernels from the hybrids dif- accessibility of substrate to the ruminal microor- fered in their rumen degradablity kinetics, with the ganisms was rate limiting with larger kernel size. greatest difference occurring between H6 (i.e., 2000 The tendency for hybrid × processing interaction CHU rating) and the other hybrids. The lower ED for ED6 and ED8 occurred because processing of H6 may have been due to its greater kernel hard- had greater effects on increasing ED of starch for ness and density resulting from the kernels being earlier maturing hybrids. The results indicate that more mature as indicated by kernel DM content. short-season hybrids, especially those with low In contrast, greater ED of H2 (i.e., 2175 CHU rat- CHU rating that mature early (i.e., H6), may have ing) compared with the other hybrids could not be lower ED of DM and starch, and would benefit directly attributed to differences kernel character- from aggressive kernel processing during harvest. istics as these were relatively similar for all hybrids This is somewhat surprising given the relatively excluding H6. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 437 early stage of maturity of the kernels in the pres- of the corn endosperm depends on the constitu- ent study. Harvesters equipped with onboard pro- ent proteins (quantity of zein) and starch (crystal- cessing rolls that reduce particle size of kernels linity) (Gayral et  al., 2016). However, the lack of are increasing used in commercial corn silage significant correlations between kernel properties production to increase starch digestibility (Heguy and prolamin content, together with the relatively et al., 2016). small differences in prolamin content of the vari- Ramos et  al. (2009) processed corn to three ous hybrids, suggests that the hybrids may have sizes that were similar to those used in the pres- been relatively similar in terms of endosperm type. ent study: ground through 3-mm sieve (526  μm), These results suggest that the observed differences cracked with a roller mill (1,360 μm), and cracked to in kernel hardness and density among hybrids were large particles (2,380 μm). Those authors observed mainly due to differences in kernel stage of matu- that the degradability of starch increased linearly rity at harvest. as the particle size decreased, but when kernels with The positive correlations between DM con- the same particle size were compared, the degrad- tent, kernel hardness, kernel density and the neg- ability differed among genotypes with a linear neg- ative correlations between those variables and ED ative effect of vitreousness. The authors concluded indicate that kernel characteristics affected starch that when corn grain is milled, genotype (i.e., vit- availability in the rumen. Thus, as kernel filling reosity) is the main limiting factor for the access increased due to physiological maturation of the of bacteria to starch. In contrast, when kernels are plants, the rumen availability of starch was neg- only broken, the main limiting factor becomes par- atively affected. Similarly, Třináctý et  al. (2016) ticle size (i.e., granulometry) that limits access of reported that small differences in maturity of corn bacteria to starch due to less available surface area. for silage significantly influenced the degradability Although we did not measure vitreousness via man- of DM and starch. Our results support the sugges- ual dissection in the present study, prolamin protein tion by Correa et al. (2002) that density, which is a content can be used as an indication of vitreous- relatively simple inexpensive measurement, is a reli- ness. In the present study, the prolamin content var- able predictor of ruminal starch availability. ied minimally (from 8.24 to 11.34/100  g starch or 1.3 to 2.5% DM) and was considerably below the CONCLUSION threshold prolamin concentration (>4.5% of DM) Short-season corn hybrids grown for silage used to designate vitreous corn starch. Thus, differ- production in Lacombe, AB, differed in rumen ences in rumen degradation characteristics among degradability of DM and starch, most likely due hybrids were probably not related to vitreousness to differences in maturity at harvest that affected of the endosperm. kernel hardness and density. Differences in degrad- ability were mainly due to rate of disappearance, Correlations which was highly correlated to kernel density. Thus, hybrids with low CHU ratings may have low effect- The negative correlation between kernel DM ive rumen degradability of starch, especially if ensil- content and CHU rating is consistent with the ing time is short. Increasing the degree of kernel expectation that hybrids with lower CHU rating processing enhanced rumen degradability of starch mature earlier (Baron  et al., 2014a). Advanced for all hybrids. Thus, regardless of CHU rating of maturity increased density and hardness of kernels hybrids, kernel processing during silage making as indicated by positive correlations between kernel is recommended as a means of enhancing rumen DM content, hardness, and density. Correa et  al. availability of starch for short-season corn hybrids. (2002) reported a strong linear correlation between kernel hardness and density for 14 dent and 5 flint LITERATURE CITED hybrids. Thus, it is possible that in the present study differences in kernel hardness were also due Andrae, J. G., C. W. Hunt, G. T. Pritchard, L. R. Kennington, to genetic differences among hybrids. Short-season J. H. Harrison, W. Kezar, and W. Mahanna. 2001. Effect of hybrid, maturity, and mechanical processing of corn corn hybrids contain flint genetics in their pedigree silage on intake and digestibility by beef cattle. J. Anim. to increase cold and drought tolerance and to pro- Sci. 79:2268–2275. doi:10.2527/2001.7992268x mote early maturation. Flint-endosperm hybrids AOAC. 2005. Official methods of analysis. 18th ed. contain a greater proportion of vitreous endo- Gaithersburg (MD): AOAC International. sperm in the kernel making them harder (Larson ASABE Standard. 2008. Method of determining and express- and Hoffman, 2008). Hardness or vitreousness ing fineness of feed materials by sieving, ASABE S319.3. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 438 Miorin et al. St. Joseph (MI): American Society of Agricultural Larson, J., and P. C. Hoffman. 2008. Technical note: a method Engineers. to quantify prolamin proteins in corn that are negatively Baron, V., K. A.  Beauchemin, P.  Juskiw, and R. R.  Doce. related to starch digestibility in ruminants. J. Dairy Sci. 2014a. Managing short-season corn and small-grain silage 91:4834–4839. doi:10.3168/jds.2008-1378 in Western Canada. In: Proceedings of the 35th Western Mahanna, B., and L. E.  Chase. 2003. Practical application Nutrition Conference, University of Alberta, Edmonton, and solutions to silage problems. In: Silage science and AB, Canada. p. 147–162. technology. Chapter  19. Agronomy Monograph No. 42. Baron, V. S., R. R.  Doce, J.  Basarab, and C.  Dick. 2014b. Fitchburg (WI): American Society of Agronomy, Crop Swath-grazing triticale and corn compared to barley and a Science Society of America, Soil Science Society of traditional winter feeding method in central Alberta. Can. America. p. 855–895. J. Plant Sci. 94:1125–1137. National Academies of Sciences, Engineering, and Medicine Blandino, M., M.  C. Mancini, A. Peila, L. Rolle, F. Vanara, (NASEM). 2016. Nutrient requirements of beef cat- and A.  Reyneri. 2010. Determination of maize kernel tle. 8th rev. ed. Natl. Acad. Press, Washington, DC. hardness: comparison of different laboratory tests to pre- doi:177226/19014 dict dry-milling performance. J. Sci. Food Agric. 90:1870– Nellis, S. E., P. C. Hoffman, and R. D. Shaver. 2013. Technical 1878. doi:10.1002/jsfa.4027 note: a modified method to quantify prolamin proteins in Brown, D. M., and A.  Bootsma. 1993. Crop heat units for dry and high-moisture corn. J. Dairy Sci. 96:4647–4652. corn and other warm-season crops in Ontario. Ontario doi:10.3168/jds.2013-6575 Ministry of Agriculture and Food Factsheet No. 93–119, Philippeau, C., F. Le Deschault de Monredon, and Agdex 111/31. 4 pp. [accessed September 16, 2016]. http:// B.  Michalet-Doreau. 1999. Relationship between www.omafra.gov.on.ca/english/crops/facts/93–119.htm. ruminal starch degradation and the physical char- Canadian Council on Animal Care. 1993. Guide to the care acteristics of corn grain. J. Anim. Sci. 77:238–243. and use of experimental animals (revised 2017). 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Increasing harvest maturity of whole-plant Unterseer, S., S. D.  Pophaly, R.  Peis, P.  Westermeier, corn silage reduces methane emission of lactating dairy cows. M.  Mayer, M. A.  Seidel, G.  Haberer, K. F.  Mayer, J. Dairy Sci. 99:354–368. doi:10.3168/jds.2015-10047 B. Ordas, H. Pausch, et al. 2016. A comprehensive study Heguy, J. M., D. Meyer, and N. Silva-Del-Río. 2016. A survey of the genomic differentiation between temperate dent of silage management practices on California dairies. J. and flint maize. Genome Biol. 17:137. doi:10.1186/ Dairy Sci. 99:1649–1654. doi:10.3168/jds.2015-10058 s13059-016-1009-x Hoffman, P.C., and R. D.  Shaver. 2009. Corn biochemis- Wiersma, D. W., P. R. Carter, K. A. Albrecht, and J. G. Coors. try: Factors related to starch digestibility in ruminants. 1993. Kernel milkline stage and corn forage yield, quality, In: Dairy Health and Nutrition Conference, Cornell and dry matter content. J. Prod. Agric. 6:94–99. University, New York, NY. Windle, M. 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In situ rumen degradation of kernels from short-season corn silage hybrids as affected by processing,

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Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of kernels from short-season corn silage hybrids as 1,2 affected by processing ,† † ‡ †,3 Renan L. Miorin,* Lucia Holtshausen, Vern Baron, and Karen A. Beauchemin *Departamento de Zootecnia, Universidade Estadual de São Paulo, Jaboticabal, SP, Brazil; Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB T1J 4B1, Canada; and Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, Lacombe, AB T4L 1W1, Canada ABSTRACT: The objective of this in situ study Differences in digestion kinetics among hybrids was to evaluate the rumen degradability of ker- were generally more pronounced for starch than nels from short-season corn hybrids grown for DM. The hybrids differed in starch degradability silage in Western Canada (Lacombe, AB) and (P  <  0.05), with earlier maturing hybrids having determine whether decreasing kernel particle lower A  fraction, lower k , and lower ED, with size would enhance ruminal degradability in a hybrid effects on ED being accentuated with faster similar manner for all hybrids. The study was a passage rate. Kernel DM content (r  =  −0.85, completely randomized design with 3 beef cows −0.87), hardness (r = −0.89, −0.86), and density (replicates) and a 6 (hybrid) × 3 (particle size) (r = −0.84, −0.85) were negatively correlated with factorial arrangement of treatments. Kernels ED4 and ED8 of starch, respectively, due mainly were processed to generate three different parti- to decreased k of fraction B. Reducing the par- cle sizes: large (2.3 mm), medium (1.4 mm), and ticle size of kernels increased ED of starch due small (0.7  mm). Processed samples were incu- to increased A fraction and k of the B fraction. bated in the rumen for 0, 3, 6, 12, 24, and 48  h A  tendency (P  =  0.09) for hybrid × processing using the in situ method and degradation kinet- effects for ED6 and ED8 indicated that process- ics of DM and starch were determined. Effective ing had greater effects on increasing ED of starch rumen degradability (ED) was estimated using for earlier maturing hybrids. We conclude that a passage rate of 0.04 (ED4), 0.06 (ED6), and short-season hybrids that mature early may have 0.08/h (ED8). Hybrids exhibited a range in whole lower ED of DM and starch and would benefit plant DM content (23.7 to 25.0%), starch con- from prolonged ensilage time. Kernel process- tent (15.9 to 28.1% DM), kernel hardness (21.9 to ing during silage making is recommended for 34.4 s/20 g) and density (3.57 to 4.18 g/mL), and short-season corn hybrids as a means of enhanc- prolamin content (8.24 to 11.34  g/100  g starch). ing rumen availability of starch. Key words: corn heat unit, corn silage, degradability, grain processing, starch © Crown copyright 2018. Transl. Anim. Sci. 2018.2:428–438 doi: 10.1093/tas/txy084 INTRODUCTION This study was conducted with financial sup - Corn silage is used extensively in cattle diets port from the Beef Cattle Research Council worldwide. Development of corn hybrids that (Canada) and Agriculture and Agri-Food Canada. require a short growing season together with Lethbridge Research and Development Centre contribu- changes in climate have led to increased corn tion number: 38718023. 3 silage acreages in areas with colder climates such Corresponding author: karen.beauchemin@agr.gc.ca as parts of Canada, Asia, and Northern Europe Received June 11, 2018. Accepted July 3, 2018. (Ramirez-Cabral et al., 2017). Corn silage can be 428 Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 429 a good alternative to other forages for beef and Development Centre Animal Care Committee in dairy cattle because of its high DM yield and compliance with the guidelines of the Canadian high total digestible nutrient content [National Council on Animal Care (1993). Academies of Sciences, Engineering, and Medicine (NASEM), 2016]. Corn Hybrids and Kernel Preparation Corn hybrids marketed in Canada are rated for Six short-season corn hybrids (H1 to H6) were maturity using the corn heat unit (CHU) system grown in 2015 at Lacombe, AB (latitude: 52°28′N; (Brown and Bootsma, 1993). This rating indicates longitude, 113°45′W), an area with fine sandy loam the number of accumulated thermal units needed soil and Orthic black soil classification. Lacombe for corn to reach maturity. Areas within Canada has a long-term CHU rating of 1800 to 2000. are mapped according to long-term weather data During the study year, 1,837 CHU accumulated and hybrids are then selected such that their CHU between seeding and harvest; thus, the year was rating fits within the CHU rating of the location in relatively cool but within the long-term average for which they are grown. Short-season corn hybrids the location (Table  1). The hybrids were selected are of flint and dent genetic populations, with flint to provide a range in CHU ratings suitable for the heritage used to confer early silking dates, cool tem- area (2,000 to 2,200 CHU). Hybrids H1 (7632HR, perature and drought tolerance, and resistance to 2,200 CHU), H4 (39M26, 2,100 CHU), H5 (7213R, kernel damage during combining (Unterseer et al., 2,050 CHU), and H6 (39F44, 2,000 CHU) were 2016). obtained from Pioneer Hi-Bred (Johnston, IA), Corn grain has a protein matrix in its endo- whereas H3 (Edge, 2,015 CHU) was from Elite sperm that protects the starch granules. Hybrids (Saint-Hyacinthe, QC) and H2 (2262RR, 2,175 of flint origin have greater proportion of vitreous CHU) from Pickseed (Lindsay, ON). The hybrids endosperm in the kernel making the starch harder were seeded (average plot size of 11.0 m ) on May to degrade because it is protected by a thick pro- 5 (74,000 seeds/ha and row spacing 75  cm using tein matrix that hinders access of ruminal bac- two-row corn planter, John Deere), The corn was teria to the site of digestion (Szasz et  al., 2007; not irrigated but received 278.6  mm of precipita- Hoffman and Shaver, 2009; Rossi et al., 2016). In tion during the growing season. Inorganic fertil- contrast, hybrids of dent origin have greater pro- izer was applied to the plots to supply 212 kg/ha N, portion of floury endosperm and thus have more 60 kg/ha P, and 72 kg/ha K. The hybrids were har- digestible starch because the granules are loosely vested on September 15 because frost was forecasted packed and the surrounding protein matrix is thin- to occur later in the week (minimum temperature ner (Hoffman and Shaver, 2009; Rossi et al., 2016). was −2.0 °C and −0.2 °C on September 17 and 18, It is uncertain whether starch degradability of 2015, respectively). short-season corn hybrids grown for silage is lim- At harvest, five ears from each hybrid were col - ited by genetic origin, and whether extensive pro- lected, frozen (−20 °C), and shipped to Lethbridge, cessing is needed to maximize rumen availability. AB. The remaining plants were harvested and a Kernel processing during harvesting for silage can 5-kg representative sample was dried at 55 °C to a minimize the effects of kernel hardness and vitre- constant weight and used to determine whole plant ousness on starch digestibility; thus, it is possible starch and NDF contents. Silk and husks were that starch degradability of short-season hybrids could be increased by more extensive processing (Philippeau et al., 1999; Andrae et al., 2001; Szasz Table  1. Corn heat unit (CHU) rating and whole et al., 2007). plant nutrient and physical composition of corn The objective of this in situ study was to evalu- hybrids grown at Lacombe, AB, Canada in 2015 ate the degradability of kernels from short-season Hybrids CHU DM, % CP, % DM Starch, % DM NDF, % DM corn hybrids grown for silage in Western Canada H1 2,200 23.7 8.02 15.9 54.4 (Lacombe, AB) and determine whether process- H2 2,175 24.9 8.21 16.4 53.9 ing to decrease particle size would enhance kernel H3 2,150 25.7 8.04 18.2 53.3 degradability. H4 2,100 23.7 8.09 21.8 51.1 H5 2,050 24.2 8.34 19.7 54.1 H6 2,000 25.0 8.31 28.1 50.5 MATERIALS AND METHODS Accumulated CHU, calculated starting from the day following three Animal handling and care procedures were consecutive days after seeding with mean daily temperature ≥12.8 °C approved by the Lethbridge Research and until harvest, were 1,837 at Lacombe, AB, in 2015. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 430 Miorin et al. removed from the cobs, frozen cobs were broken in required to produce 17  mL of flour when a 20-g half, and 10 kernels were removed from the edge of sample of air-dried kernels is passed through a cut- each half and dried at 55 °C to a constant weight ter mill (Retsch GmbH, Haan, Germany) equipped to determine DM content of kernels. The cobs were with a 2-mm screen. Density was measured as the then air-dried in a temperature controlled, well ven- weight of the ground sample (g/mL). tilated room until dry. Kernels were removed from Mean size by mass (mm) of the processed ker- the cobs using a lab-scale sheller and retained for nels used in the in situ study was determined using the study. a sieve shaker (Ro-Tap, W.S. Tyler, Mentor, OH) equipped with eight sieves arranged in descending order (4.75, 2.36, 1.18, 0.6, 0.425, 0.3, 0.212, and Treatments 0.096  mm) above a collection pan. A  subsample The study was a completely randomized design (100  g) of air-dried kernels from each processed with 3 beef cows (replicates) and a 6 (hybrid) × 3 hybrid was placed on the top sieve and shaken con- (particle size) factorial arrangement of treatments. tinuously for 10  min. Weight over size generated The kernels from each hybrid were processed to during this procedure was used to compute the generate three different particle sizes (Table  2): geometric mean diameter size and standard devi- large (cracked with hammer), medium (chopped ation (SD ), according the ASABE Standard gmd using a Ninja blender, SharkNinja Co., Champlain, (2008) methodology. The assumption is that par- NY), and small (ground through a 2-mm screen, ticle size of ground feeds is logarithmic-normally standard model 4 Wiley Mill, Arthur Thomas Co., distributed. Philadelphia, PA). Geometric mean diameter (mm) was calculated as follows: Physical Measurements   (l Wi og di ) −1   Geometricmeandiametersizel = og Kernel hardness (Table  3) of whole kernels   Wi   was determined using the Stenvert test (Blandino et al., 2010), which measured the time (in seconds) where Wi = weight (g) on the ith sieve. Table  2. Geometric mean diameter size (GMD, In Situ Measurements mm) and standard deviation (SD ) of processed gmd Ruminal degradation of DM and starch was kernels from short-season corn silage hybrids grown determined using the in situ method as adapted by in Lacombe, AB, Canada Griffith et  al. (2017) . Three mature, ruminally can- Size nulated beef cows (mean ± SD; 650  ±  30  kg BW) Large Medium Small were offered for ad libitum intake a diet consisting GMD, mm SD GMD, mm SD GMD, mm SD Hybrid gmd gmd gmd of 19% barley grain, 62% corn silage, 13% corn dis- H1 2.39 0.29 1.29 0.28 0.68 0.19 tillers dried grains, and 6% vitamin/mineral supple- H2 2.19 0.29 1.40 0.29 0.71 0.20 ment (DM basis). Approximately 6 g of each hybrid H3 2.22 0.29 1.36 0.28 0.74 0.20 sample was weighed in duplicate into 10  ×  18  cm H4 2.21 0.28 1.36 0.30 0.71 0.22 polyester bags (R1020, ANKOM Technology, H5 2.38 0.28 1.59 0.30 0.69 0.21 Macedon, NY; 50-μm porosity). The bags were H6 2.41 0.27 1.48 0.30 0.74 0.21 sealed, placed inside larger mesh bags (30 × 30 cm) Log-normal SD. with three equal-sized channels sewn into them to Table  3. Nutrient and physical composition of the corn hybrid kernels during the growing season at Lacombe, AB, Canada in 2015 Hybrid DM, % DM Starch, % DM Hardness, s/20 g Density, g/mL Prolamin, g/100 g starch H1 35.8 60.4 21.9 3.57 8.24 H2 37.3 59.0 23.2 3.70 10.01 H3 39.9 57.6 24.9 3.86 8.29 H4 45.8 56.4 24.9 4.04 11.34 H5 43.8 60.0 28.2 3.81 10.22 H6 49.7 58.2 34.4 4.18 10.51 Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 431 keep the smaller polyester bags from aggregating 2005) by drying samples at 135 °C for 2 h, followed together. Three polyester bags were placed in both by hot weighing. The original kernels and bag outside channels of the larger mesh bags, and two residues were ground using a ball grinder (Mixer were placed in the middle channel of the mesh bags. Mill MM2000; Retsch, Haan, Germany) prior to There were a total of eight polyester bags per mesh determination of starch content in duplicate by bag and one mesh bag per time point. All bags were enzymatic hydrolysis of α-linked glucose polymers inserted in the rumen at 0900, just before the morn- as described by Chung et  al. (2011). The original ing meal. The bags were removed following 3, 6, 12, ground kernel samples were also used to determine 24, and 48 h of ruminal incubation. After removal, prolamin content in duplicate as described by Nellis bags were rinsed in cold water with ice and washed et al. (2013). For analysis of the whole plant mate- in cold water until clean. To estimate the soluble and rial, the dried samples were ground through a 1-mm washout fraction, 0-h bags were not inserted into the screen (standard model 4 Wiley Mill) and analyzed rumen, but were washed following the same process in duplicate for analytical DM content (method as previously described. Cows were the replicates, 930.15; AOAC, 2005), NDF (Ankom 200 system, such that for each incubation time 54 bags were incu- ANKOM Technology, Fairport, NY; heat-stable bated (6 hybrids × 3 particle sizes × 3 cows), total- α-amylase and sodium sulfite used in the assay), ing 324 bags (54 bags × 6 times) for the study. Bags and starch content as previously described. and residues were dried in a 55  °C forced-air oven for a minimum of 48 h. Dried bags with residue were Statistical Analysis weighed to determine DM disappearance (DMD). If Data for digestion kinetics were analyzed with the coefficient of variation was >10%, the bags were the MIXED procedure of SAS 9.2. The model reweighed or the outlier duplicate bag was discarded. included fixed effects of hybrid, particle size, The residues from each bag were analyzed for starch and their interaction, and cow as random effect. content to determine starch disappearance. Correlations were calculated using the CORR pro- The degradation kinetics of each hybrid and cedure of SAS 9.2. Means were declared signifi - treatment were calculated using the NLIN proce- cantly different when P < 0.05. dure in SAS program. Dry matter and starch dis- appearance values for the individual bags at each RESULTS time point were fitted to an exponential model: −kt Disappearance () tA =+ B () 1 − e Characterization of the Hybrids and Kernels where A  =  rapidly degradable fraction and wash- It was not possible to statistically evaluate out fraction (%); B  =  potentially degradable frac- −1 hybrid differences in chemical composition because tion (%); k  = degradation constant rate (h ), and there was only one field replication of each hybrid. t = incubation time (h). The hybrids ranged minimally in DM content from Effective ruminal degradability (ED) of DM 23.7% to 25.7%, yet starch content varied widely and starch was calculated according to equation: from 15.9 to 28.1% DM (Table  1). The CP (8.02   k to 8.34% DM) and NDF (50.5 to 54.4% DM) con- ED =+ AB   tents also varied minimally. The geometric mean kk +   dp diameter size and S of kernels from the hybrids gmd where k was the fractional ruminal passage rate after processing indicated that large, medium, and −1 (h ), which was assumed to be 0.04 (ED4), 0.06 small particles were obtained as planned (Table 2). (ED6), and 0.08 (ED8). The DM content of kernels at harvest varied from 35.8% to 49.7%, whereas starch content varied min- imally from 56.4 to 60.4% DM (Table  3). Kernel Chemical Analysis hardness varied from 21.9 to 34.4  s/20  g, density Whole kernels were weighed fresh and then ranged from 3.57 to 4.18 g/mL, and prolamin con- dried in a forced-air oven to a constant weight for tent ranged from 8.24 to 11.34 g/100 g of starch. the determination of kernel dry weight. Dried ker- nels were ground through a 2-mm screen (stand- DM and Starch Disappearance ard model 4 Wiley Mill; Arthur Thomas Co., Philadelphia, PA) and analyzed in duplicate for Differences among hybrids for DMD occurred analytical DM content (method 930.15; AOAC, at 0, 3, 6, and 24 h (P < 0.001; Table 4). Between 0 Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 432 Miorin et al. Table  4. Influence of hybrid and particle size Table  5. Influence of hybrid and particle size on on ruminal DM disappearance for kernels from ruminal starch disappearance for kernels from short-season corn hybrids grown in Lacombe, AB, short-season corn hybrids grown in Lacombe, AB, Canada Canada Incubation time, h Time (h) 0 3 6 12 24 48 0 3 6 12 24 48 Hybrid Hybrids a a a a b a ab a a a H1 25.6 43.6 52.0 55.7 83.5 92.3 H1 13.5 39.3 46.4 53.6 89.6 96.5 ab ab a a a a a a ab a H2 24.6 42.0 52.6 51.7 82.5 90.5 H2 20.4 40.9 50.8 52.7 88.7 97.6 b bc b a a b b a ab a H3 23.9 40.0 48.0 47.8 80.1 92.6 H3 19.8 32.2 42.4 44.9 83.8 95.9 c abc b a b b c a b ab H4 21.5 41.2 47.9 51.3 79.1 89.5 H4 13.5 31.8 35.1 50.6 82.2 93.2 c c b a ab b b a ab a H5 20.9 39.1 48.4 50.0 82.0 90.2 H5 15.3 31.0 44.6 46.8 85.7 94.0 d d c b b c d b c b H6 19.7 33.1 41.4 42.9 68.3 85.9 H6 13.4 21.7 29.1 31.4 64.2 87.9 SEM 0.67 2.70 2.70 6.05 4.76 4.57 SEM 3.04 4.42 3.88 7.38 5.23 4.02 Size Size c c c c b c c b b b Large 18.4 33.8 43.9 45.8 73.0 84.4 Large 10.9 25.5 36.8 42.4 74.7 87.8 b b b b a b b b b a Medium 21.7 40.2 47.4 50.4 78.1 91.3 Medium 16.3 33.3 37.5 47.0 79.3 95.9 a a a a a a a a a a Small 28.0 45.5 53.8 53.5 86.6 94.9 Small 20.7 39.7 49.9 50.6 93.1 98.8 P-value P-value Hybrid <0.001 <0.001 <0.001 0.160 <0.001 0.173 Hybrid 0.018 <0.001 <0.001 <0.001 <0.001 0.017 Size <0.001 <0.001 <0.001 0.088 <0.001 <0.001 Size <0.001 <0.001 <0.001 0.151 <0.001 <0.001 Hybrid × size 0.289 0.920 0.005 0.951 0.568 0.470 Hybrid × size 0.019 0.751 0.006 0.653 0.199 0.419 a–d a–d Means in the same column within hybrid and size categories with- Means in the same column within hybrid and size categories with- out a common subscript letter differ at P < 0.05. out a common subscript letter differ at P < 0.05. and 24 h of incubation (except 12 h), DMD of H6 degradable fraction (B) (P ≥ 0.179), with no interac- was clearly less than that of other hybrids (P < 0.05), tions (P ≥ 0.417) between hybrid and size (Table 6). but after 48 h of incubation hybrid differences were The soluble fraction A  was greater (P  <  0.05) for minimal (P = 0.173). Particle size influenced DMD H1 and H2 compared with the others, with hybrid at all incubation times (P < 0.001, except P = 0.088 H6 having the lowest soluble fraction, although at 12  h), with clear differences among the three not statistically different from H5 (P > 0.05). The particle sizes until 24 h. After 48 h, large particles rate of degradation (k ) (P  <  0.05) was lower for had lower DMD than the other particles (P ≤ 0.05), H6 compared with all other hybrids. Differences with no difference (P > 0.05) between medium and among hybrids for ED depended upon the rumen small particles. passage rate. With a slow passage rate, hybrid H6 Differences among hybrids (P ≤ 0.017) for had lower ED4 than the others (P < 0.05). With a starch disappearance occurred at all incubation medium passage rate, H6 had lower ED6 than the times (Table  5, Figures  1 and 2). Disappearance others (P < 0.05), but H4 also ranked lower than H2 of starch was always lower for H6 than for other (P < 0.05). For ED8, H6 remained lower than the hybrids (P  <  0.05), except at 0  h when it differed others (P < 0.05), but H3 and H4 also ranked lower only from H2 and H3 and at 48 h when it did not than H2 (P < 0.05). Thus, ED of DM was positively differ from H4. Particle size influenced starch dis - associated with CHU rating of the hybrid, and dif- appearance at almost all incubation times (Table 5, ferences in the degradability of hybrids increased as Figure 3). For the short incubation times of 0 and passage rate increased. The A fraction, ED4, ED6, 3 h the three sizes differed (P < 0.05), at 6 and 24 h and ED8 differed for large, medium, and small par- large and medium particles differed from small par- ticles (P  <  0.05), whereas k was similar for large ticles (P < 0.05), and at 48 h small and medium were and medium particles, but 33% greater for small similar but differed from large particles (P < 0.05). particles (P < 0.05). DM Degradation Kinetics Starch Degradation Kinetics The kinetics of DM degradation showed sig- For the kinetics of starch degradation (Table 7), nificant differences ( P  <  0.001) due to hybrid and significant ( P < 0.001) hybrid and particle size effects particle size for all variables except the potentially were observed for all variables (except size effect for Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 433 Figure  1. Influence of short-season corn hybrid and particle size on ruminal starch disappearance from kernels.  Symbols indicate observed values, while lines indicate predicted values based on Table 7. fraction B, P  =  0.122), and there was a tendency hybrids, H6 was consistently lowest, and the others for an interaction for ED6 (P  =  0.099) and ED8 were intermediate (P < 0.05). Hybrid H4 had lower (P = 0.070). Fraction A (P < 0.05) was greater for H2 ED (P < 0.05) than the other intermediate hybrids, compared with the other hybrids, with H4 and H6 when the passage rate was faster (ED6 and ED8). being lowest. The potentially degradable B fraction Thus, earlier maturing hybrids had lower A fraction, was lowest for H2, and greatest for H1, H4, and H6 lower k , and lower ED, with hybrid effects on ED (P < 0.05). For k , H6 was lower (P < 0.05) than all being accentuated with faster passage rate. others, which were similar. For ED (ED4, ED6, and Decreasing the particle size of the incubated ED8), H2 was consistently greater than the other material increased ED (P < 0.001), regardless of Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 434 Miorin et al. Figure 2. Influence of short-season corn hybrid on ruminal starch disappearance from kernels. Symbols indicate observed values, whereas lines indicate predicted values based on Table 7. Figure 3. Influence of particle size of kernels (large, medium, small) on ruminal starch disappearance for short-season corn hybrids. Symbols indicate observed values, whereas lines indicate predicted values based on Table 7. passage rate, mainly due to an increase in fraction small and medium sized particles on disappear- A and an increase in k for small vs. medium and ance were less for the later maturing hybrids. large particles (Table 7). The tendency for interac- tion between hybrid and size for ED6 (P = 0.099) Correlations and ED8 (P = 0.070) indicates that with a faster rate of passage, the effects of particle size reduc- There were positive correlations between tion on ED tended to differ among hybrids. The kernel DM content and hardness and density of interaction effects between hybrid and size on kernels (Table  8), and these characteristics were starch disappearance (observed and predicted) is negatively correlated with CHU rating of the shown in Figure  1. Processing the kernels had a hybrid, ED4 and ED8. As hardness and density much greater effect on starch disappearance of increased, k of starch degradation decreased. the earlier maturing hybrids (H3, H4, H5, and There was also a significant negative correlation H6) than for the later maturing hybrids (H1, between the A and B fractions (P < 0.01), where H2). Furthermore, the earlier maturing hybrids hybrids with a greater A fraction had less B frac- required fine processing to maximize starch dis - tion. In addition, there were positive correlations appearance, whereas the differences between between A, ED4, and ED8, where hybrids with Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 435 Table  6. Influence of hybrid and particle size Table  7. Influence of hybrids and particle sizes on ruminal DM disappearance for kernels from on ruminal starch disappearance for kernels from short-season corn hybrids grown in Lacombe, AB, short-season corn hybrids grown in Lacombe, AB, Canada Canada Item Item 1 2 3 −1 4 5 6 2 3 4 −1 5 6 7 A, % B, % k , h ED4, % ED6, % ED8, % A, % B, % k , h ED4, % ED6, % ED8, % d d 1 1 Hybrids Hybrids a a a ab ab bc ab a b b b H1 27.5 67.9 0.065 69.2 62.5 57.7 H1 15.8 83.1 0.069 67.9 59.8 53.9 a a a a a a c a a a a H2 27.0 68.6 0.069 69.8 63.1 58.2 H2 24.2 74.9 0.071 71.4 64.1 58.8 ab a a ab b b b a bc b b H3 25.4 71.4 0.063 67.8 60.8 55.8 H3 17.2 81.4 0.068 66.9 59.0 53.3 bc a a b b cd a a c c c H4 24.2 71.2 0.064 67.5 60.4 55.4 H4 11.1 88.4 0.062 64.1 55.3 49.1 cd a a ab ab bc b a bc b b H5 22.7 71.7 0.074 68.5 61.6 56.5 H5 15.1 81.5 0.072 66.8 58.9 53.2 d b b c c d ab b d d d H6 21.5 73.8 0.043 58.3 51.1 46.3 H6 9.88 87.5 0.042 53.1 44.7 39.1 SEM 1.30 3.85 0.007 2.36 2.20 2.05 SEM 2.84 3.84 0.008 2.91 2.89 2.82 Size Size c b c c c c b c c c Large 20.5 71.7 0.055 61.4 54.0 49.0 Large 11.1 84.9 0.052 58.4 49.9 44.1 b b b b b b b b b b Medium 24.5 71.9 0.058 66.2 59.3 54.2 Medium 16.0 83.2 0.058 64.1 55.9 50.1 a a a a a a a a a a Small 29.0 68.6 0.075 73.1 66.5 61.7 Small 19.6 80.3 0.082 72.7 65.1 59.5 P-values P-values Hybrid <0.001 0.316 <0.001 <0.001 <0.001 <0.001 Hybrid <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Size <0.001 0.179 <0.001 <0.001 <0.001 <0.001 Size <0.001 0.122 <0.001 <0.001 <0.001 <0.001 Hybrid × size 0.705 0.786 0.496 0.640 0.521 0.417 Hybrid × size 0.159 0.703 0.305 0.139 0.099 0.070 a–d a–d Means in the same column within hybrid and size categories with- Means in the same column within hybrid and size categories with- out a common subscript letter differ at P < 0.05. out a common subscript letter differ at P < 0.05. 1 1 Rapidly degradable fraction (%). Hybrids grown at Lacombe, AB, were within 2,000–2,200 CHU. 2 2 Slowly degradable fraction (%). Rapidly degradable fraction, %. 3 −1 3 Degradation rate constant (h ) of fraction B. Slowly degradable fraction, %. 4 4 −1 Effective degradability (%) with fractional passage rate of 0.04/h. Degradation constant rate, h . 5 5 Effective degradability (%) with fractional passage rate of 0.06/h. Effective degradability, with fractional passage rate of 4.0%/h. 6 6 Effective degradability (%) with fractional passage rate of 0.08/h. Effective degradability, with fractional passage rate of 6.0%/h. Effective degradability, with fractional passage rate of 8.0%/h. greater fraction A were more degradable. In con- trast, fraction B showed an inverse correlation Thus, this study aims to show potential differ- with ED. ences among hybrids adapted to a given location, rather than provide specific information for indi - DISCUSSION vidual hybrids. The corn hybrids used in the study were not ensiled; thus, the results indicate the effects of hybrid and particle size on ruminal degradation Characterization of the Hybrids and Kernels without the confounding effects of ensiling. The ensilage process would be expected to further The CHU ratings of the hybrids (Table  2) to increase ruminal starch degradability by 8 to 10 per- reach grain maturity exceeded the CHU received centage points after 3 mo in the silo (Der Bedrosian during the growing season. This is typical practice et  al., 2012; Windle et  al., 2014). Although whole for short-season growing areas as corn hybrids with plant corn is typically ensiled prior to feeding, in <2000 CHU rating are not commercially available. some cases, silage is fed prior to the optimum ensil- Because of the cool climate of this region, corn is ing duration because of limited feed supply (Heguy grown for silage rather than grain. In some years, et al., 2016). Furthermore, there is increasing use of the DM content at the end of the growing season direct grazed and swathed grazed whole plant corn is below the minimum recommended level of 30% for ensilage (Mahanna and Chase, 2003) especially for beef cattle (Baron et al., 2014b). for hybrids with greater CHU ratings. Because of The hybrids were grown in a single year and low temperatures and risk of frost, it is not possi- location. It is well known that maturity at har- ble to extend the growing season to increase matu- vest and chemical composition of a hybrid can rity at harvest. Such was the case in the present vary due to environmental growing conditions. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 436 Miorin et al. Table 8. Pearson correlation coefficients among variables for kernel characteristics and degradation kinet - −1 ics of starch with effective degradability estimated using a fractional passage rate of 0.04 h (ED4) and −1 0.08 h (ED8) Item Hardness Density CHU Starch Prolamin A B k ED4 ED8 DM 0.87* 0.94** −0.95** −0.49 0.72 −0.79 0.72 −0.77 −0.85* −0.87* Hardness 0.80* −0.94** −0.15 0.45 −0.61 0.48 −0.81* −0.89** −0.86* Density −0.83* −0.70 0.65 −0.71 0.69 −0.82* −0.84* −0.85* CHU 0.22 −0.63 −0.69 −0.55 0.69 0.81* 0.80* Starch −0.46 0.36 −0.47 0.38 0.31 0.36 Prolamin −0.38 0.37 −0.39 −0.38 −0.40 A,% −0.97** 0.69 0.80* 0.86* B,% −0.67 −0.75 −0.81* −1 k , h 0.96** 0.95** ED4, % 0.99** *P < 0.05. **P < 0.01. study where whole plant DM averaged (mean ± Greater differentiation in degradability kinet- SD) 24.5  ±  0.80%. The range in starch content of ics among the hybrids occurred when ED was the whole plant material from 15.9 to 28.1% DM estimated using a faster passage rate (i.e., ED8 vs. indicated that kernel filling was incomplete, espe - ED4), indicating that hybrid effects may be more cially for the hybrids that required greater CHU for important for dairy cows vs. feedlot cattle. Due maturity. The NDF content in corn silage declines as to faster rate of passage of feed from the rumen plants mature due to the dilution effect of increasing in dairy cows, proportionally less total tract diges- starch content (Hatew et  al., 2016); thus, the rela- tion of starch occurs in the rumen of dairy cows tively high NDF content of the whole plant hybrids compared with feedlot cattle (NASEM, 2016). (50.5 to 54.4% DM) is consistent with the low starch Shifting starch digestion from the rumen to the contents. In comparison, NASEM (2016) reported small intestine can decrease the risk of acidosis average values for corn silage grown in the United and improve the efficiency of energy yield if small States of (mean ± SD, DM basis) 33.1 ± 5.6% DM, intestinal digestibility is high (>75%) (Huntington 32.6 ± 7.0% starch, and 43.0 ± 5.5% NDF. The DM et al., 2006). However, small intestinal digestibility content of the kernels ranged from 35.8% to 49.7%, is typically only high when animals are fed at low which is consistent with the relatively immature stage intakes or when grains are highly processed; thus, of development of the hybrids at harvest. Although total tract digestibility may be reduced in dairy kernel stage of development was not measured in the cows fed short-season corn hybrids with low CHU present study, based on kernel DM content, it was rating. Furthermore, in vivo evaluations are needed probably close to early dough (Wiersma et al., 1993). to validate this hypothesis. Decreasing the particle size of the kernels increased availability of the DM and starch in the DM and Starch Degradation rumen by increasing the A fraction and k of the B fraction. Increased A fraction indicates greater Generally, differences in digestion kinetics washout and solubility occurred with smaller among hybrids were more pronounced for starch particle size, whereas increased k indicates that than for DM. The kernels from the hybrids dif- accessibility of substrate to the ruminal microor- fered in their rumen degradablity kinetics, with the ganisms was rate limiting with larger kernel size. greatest difference occurring between H6 (i.e., 2000 The tendency for hybrid × processing interaction CHU rating) and the other hybrids. The lower ED for ED6 and ED8 occurred because processing of H6 may have been due to its greater kernel hard- had greater effects on increasing ED of starch for ness and density resulting from the kernels being earlier maturing hybrids. The results indicate that more mature as indicated by kernel DM content. short-season hybrids, especially those with low In contrast, greater ED of H2 (i.e., 2175 CHU rat- CHU rating that mature early (i.e., H6), may have ing) compared with the other hybrids could not be lower ED of DM and starch, and would benefit directly attributed to differences kernel character- from aggressive kernel processing during harvest. istics as these were relatively similar for all hybrids This is somewhat surprising given the relatively excluding H6. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/article-abstract/2/4/428/5050273 by Ed 'DeepDyve' Gillespie user on 16 October 2018 In situ rumen degradation of corn kernels 437 early stage of maturity of the kernels in the pres- of the corn endosperm depends on the constitu- ent study. Harvesters equipped with onboard pro- ent proteins (quantity of zein) and starch (crystal- cessing rolls that reduce particle size of kernels linity) (Gayral et  al., 2016). However, the lack of are increasing used in commercial corn silage significant correlations between kernel properties production to increase starch digestibility (Heguy and prolamin content, together with the relatively et al., 2016). small differences in prolamin content of the vari- Ramos et  al. (2009) processed corn to three ous hybrids, suggests that the hybrids may have sizes that were similar to those used in the pres- been relatively similar in terms of endosperm type. ent study: ground through 3-mm sieve (526  μm), These results suggest that the observed differences cracked with a roller mill (1,360 μm), and cracked to in kernel hardness and density among hybrids were large particles (2,380 μm). Those authors observed mainly due to differences in kernel stage of matu- that the degradability of starch increased linearly rity at harvest. as the particle size decreased, but when kernels with The positive correlations between DM con- the same particle size were compared, the degrad- tent, kernel hardness, kernel density and the neg- ability differed among genotypes with a linear neg- ative correlations between those variables and ED ative effect of vitreousness. The authors concluded indicate that kernel characteristics affected starch that when corn grain is milled, genotype (i.e., vit- availability in the rumen. Thus, as kernel filling reosity) is the main limiting factor for the access increased due to physiological maturation of the of bacteria to starch. In contrast, when kernels are plants, the rumen availability of starch was neg- only broken, the main limiting factor becomes par- atively affected. Similarly, Třináctý et  al. (2016) ticle size (i.e., granulometry) that limits access of reported that small differences in maturity of corn bacteria to starch due to less available surface area. for silage significantly influenced the degradability Although we did not measure vitreousness via man- of DM and starch. Our results support the sugges- ual dissection in the present study, prolamin protein tion by Correa et al. (2002) that density, which is a content can be used as an indication of vitreous- relatively simple inexpensive measurement, is a reli- ness. In the present study, the prolamin content var- able predictor of ruminal starch availability. ied minimally (from 8.24 to 11.34/100  g starch or 1.3 to 2.5% DM) and was considerably below the CONCLUSION threshold prolamin concentration (>4.5% of DM) Short-season corn hybrids grown for silage used to designate vitreous corn starch. Thus, differ- production in Lacombe, AB, differed in rumen ences in rumen degradation characteristics among degradability of DM and starch, most likely due hybrids were probably not related to vitreousness to differences in maturity at harvest that affected of the endosperm. kernel hardness and density. Differences in degrad- ability were mainly due to rate of disappearance, Correlations which was highly correlated to kernel density. Thus, hybrids with low CHU ratings may have low effect- The negative correlation between kernel DM ive rumen degradability of starch, especially if ensil- content and CHU rating is consistent with the ing time is short. Increasing the degree of kernel expectation that hybrids with lower CHU rating processing enhanced rumen degradability of starch mature earlier (Baron  et al., 2014a). Advanced for all hybrids. Thus, regardless of CHU rating of maturity increased density and hardness of kernels hybrids, kernel processing during silage making as indicated by positive correlations between kernel is recommended as a means of enhancing rumen DM content, hardness, and density. Correa et  al. availability of starch for short-season corn hybrids. (2002) reported a strong linear correlation between kernel hardness and density for 14 dent and 5 flint LITERATURE CITED hybrids. Thus, it is possible that in the present study differences in kernel hardness were also due Andrae, J. G., C. W. Hunt, G. T. Pritchard, L. R. Kennington, to genetic differences among hybrids. Short-season J. H. Harrison, W. Kezar, and W. Mahanna. 2001. Effect of hybrid, maturity, and mechanical processing of corn corn hybrids contain flint genetics in their pedigree silage on intake and digestibility by beef cattle. J. 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Published: Oct 1, 2018

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