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Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 Developmental and reproductive characteristics of beef heifers classified by number of estrous cycles experienced by start of first breeding †,1 † ‡ Andrew J. Roberts, Jaclyn N. Ketchum, and Richard N. Funston † ‡ USDA–ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301; University of Nebraska West Central Research and Extension Center, North Platte, NE 69101 ABSTRACT: A retrospective analysis was con- than the 1 (90%) or >3 (94%) estrous cycles groups ducted to evaluate the effect of number of estrous and tended to differ (P < 0.1) from the 2 (88%) and cycles exhibited before breeding on growth and repro- 3 (89%) estrous cycle groups. Interval from the start ductive performance of replacement beef heifers fed of breeding to calving was 3 to 5 d longer (P < 0.05) ad-libitum or restricted by 20% less than ad-libitum for the 0 cycle group (300 ± 1 d) than other groups. during postweaning development over a 9-yr period. Proportion of heifers calving in the first 21 d was Progesterone concentration in blood samples col- less (P < 0.05) in the 0 or 1 cycle groups than other lected at 9- to 11-d intervals were used to assign heif- groups. Pregnancy rates of 2-yr-old cows (n = 898) ers into groups by number of estrous cycles exhibited were lowest (P < 0.05) for the 0 (73%) and 2 (79%) before the start of breeding: 0 (nonpubertal; n = 395), estrous cycle groups than the 1 (85%), 3 (90%), or >3 1 (n = 205), 2 (n = 211), 3 (n = 116), or >3 (n = 249). (92%) estrous cycle groups. Restricted level of feeding Heifers (P < 0.01) in the 0 cycle group were born 6 d during postweaning development resulted in greater later than the 1, 2, or 3 cycle groups, which were born (P < 0.05) proportion of heifers in 0 cycle group and 4 d later (P < 0.01) than the >3 cycle group. Weight lower (P < 0.05) proportion in >3 cycle group, but of heifers at birth decreased (P < 0.05) as the number reproductive performance was not influenced (P > of cycles increased. Weaning weight and ultrasound 0.1) by level of feeding or interaction of feeding and measures of loin area and fat thickness over the loin estrous cycle grouping. In summary, date of birth and at 1 yr age increased as the number of cycles increased rate of physical maturation (weight, height, and fat (P < 0.01). Postwean weight gain, hip height at 1 yr deposition) were associated with timing of puberty. age, and weights from the start of breeding through Pregnancy rate was greater in heifers that exhibited precalving increased with cycle numbers in a quad- estrus before the start of breeding, but did not improve ratic fashion (P < 0.02) and were greater (P < 0.05) from having more than one estrous cycle. Proportion in ad-libitum than restricted-fed heifers. Pregnancy conceiving early was greater for heifers having two or rate in the 0 cycle group was lower (84%; P < 0.05) more cycles before breeding. Key words: beef heifers, heifer development, puberty, reproduction © Published by Oxford University Press on behalf of the American Society of Animal Science 2018. This work is written by (a) US Government employee(s) and is in the public domain in the US. This Open Access article contains public sector information licensed under the Open Government Licence v2.0 (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/). Transl. Anim. Sci. 2018.XX:XX–XX doi: 10.1093/tas/txy118 INTRODUCTION Obtaining high-pregnancy rates in replace- ment females is a common goal among beef cattle producers. One industry guideline recom- Corresponding author: email@example.com mends that heifers should be managed so they Received August 21, 2018. achieve puberty in sufficient time to experience Accepted November 8, 2018. 1 Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 2 Roberts et al. multiple estrous cycles before the start of breed- body weight and hip height were measured on ing. This is based on research that demonstrated all heifers, and ultrasound carcass measures were a 21 percentage point increase in pregnancy rate collected on heifers from years 2 through 9 of the in heifers inseminated on their third estrus com- study, as described previously (Roberts et al., 2007). pared with heifers inseminated on their first estrus Following the 140-d trial, heifers were managed the (Byerley et al., 1987). It was concluded from these same throughout the breeding season. A prebreed- results that fertility of the first pubertal estrus was ing weight was taken 0 to 16 d (varied over years) inferior to the third estrus. Additional studies con- before the start of breeding. This population pro- firming this conclusion are lacking and substan- vided an opportunity to evaluate the objective tial genetic change in the cattle population has using heifers developed at different rates of growth occurred since these data were collected over 25 yr during the postweaning period. ago (Endecott et al., 2013). Furthermore, Byerley Circulating concentrations of progesterone were et al. (1987) had potentially confounding effects of used to estimate date of first estrus. Beginning at an heifer age and weight at time of breeding between average of 331 d of age and continuing through the treatment groups. Heifers inseminated at first estrus start of breeding, 3 to 9 mL of blood were collected were 53 d younger (322 vs. 375 d) and 31 kg lighter from each heifer by coccygeal venipuncture at 9- to (295 vs. 326 kg) than heifers inseminated on their 11-d intervals. After collection, blood was placed third estrus. The objective of this research was to on ice and stored overnight at 4°C. Blood was then provide a more thorough evaluation of the impact centrifuged at 1,200 × g for 30 min. Serum was har- the number of estrous cycles exhibited before the vested and stored at −20°C for subsequent proges- start of breeding has on pregnancy rates of replace- terone analysis. Concentrations of progesterone in ment beef heifers and to characterize growth and serum were determined directly without extraction development associated with the number of estrous by solid-phase radioimmunoassay (Coat-a-Count cycles exhibited before the start of breeding. kit; Diagnostic Products Corp., Los Angeles, CA) as reported previously (Bellows et al., 1991). Intraassay and interassay CV were 8% and 16%, MATERIALS AND METHODS respectively, and assay sensitivity was 0.08 ng/mL. All research protocols used in this study were For the purpose of this study, date of first estrus approved by the USDA, ARS, Fort Keogh Livestock was assumed to occur 6 d before the date of first and Range Research Institutional Animal Care and progesterone sample measuring ≥1 ng/mL. Heifers Use Committee. Heifers (n = 1,176) used in this were classified into one of five categories based study were a stable composite population (CGC: ½ on the estimated number of estrous cycles exhib- Red Angus, ¼ Charolais, ¼ Tarentaise; Newman ited before the start of breeding, assuming a 21-d et al., 1993) produced over a 9-yr period (average interval for each estrous cycle: category = 0 if no Julian birthdate 96 ± 15). Date and weight were progesterone sample was ≥1 ng/mL (nonpubertal, recorded for all heifers at birth and weaning. At n = 395); category = 1 if number of days between weaning, heifers were placed in a feedlot and sub- first progesterone sample ≥1 ng/mL and the start sequently assigned to either control or restricted of breeding was <15 d (n = 205); category = 2 if feeding levels for a 140-d period, beginning approxi- number of days between first progesterone sample mately 60 d after adaptation to the feedlot. In the ≥1 ng/mL and the start of breeding was 15 to 35 d first year of the study (2002), heifers were group fed (n = 211); category = 3 if number of days between in one of four pens (two pens/feeding treatment). first progesterone sample ≥1 ng/mL and the start In subsequent years, heifers were individually fed in of breeding was 36 to 56 d (n = 116); category > 3 an open shed equipped with electronic Calan gates if number of days between first progesterone sam- (American Calan, Northwood, NH) as described ple ≥ 1 ng/mL and the start of breeding was >56 previously (Roberts et al., 2007, 2009). Heifers d (n = 249). Beginning date of sampling did not averaged 245 ± 19 d of age and 220 ± 25 kg weight allow for determination of the specific number of at initiation of the feeding period. Control heif- cycles in the latter group beyond greater than three ers were fed to appetite and restricted heifers were estrous cycles. fed at 80% of that consumed by controls adjusted Beginning approximately June 1 each year, at to a common weight basis (weight measurements an average age of 425 ± 15 d (youngest and old- and feed adjustments made at 28-d intervals). The est heifer over the 9-yr period was 370 and 465 d, 140-d period ended 40 ± 11 d before the start of respectively), heifers were inseminated followed by breeding. At the end of the 140-d feeding trial, natural mating for a 48- to 55-d breeding season Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 Onset of puberty and heifer characteristics 3 (n = 5 yr) or natural mating only for a 46- or 62-d of all other variables. Estrous cycle classification breeding season (n = 4 yr). In the 5 yr estrous was considered significant when P < 0.05 for type 3 synchronization was employed, protocols varied tests of fixed effects for estrous cycle classification. across yr; with a CO-Synch protocol used in 1 yr, When significant, least square means for estrous a CO-Synch + controlled internal drug-releasing cycle classifications were compared using the DIFF device (CIDR; Zoetis Animal Health, Parssipany, option. In addition, linear and quadratic contrast NJ) protocol used for 2 yr, and protocols with statements were used to provide insight on pattern either 1 or 2 PGF injections used the other 2 yr. of change as the number of estrous cycles increased 2α Depending on the estrous synchronization proto- from 0 to >3. Values presented represent least col used, breeding season duration was adjusted square means and SE. Effects of feeding treatment to provide heifers three opportunities to be bred if on many of the response variables analyzed have pubertal at the start of breeding (i.e., breeding sea- been reported previously and are not presented in son of 48 to 55 d). At 1 to 2 mo after bull removal, this study (Roberts et al., 2017); except data on pro- body weight and hip height were measured, and portion of animals from each treatment within each heifers were evaluated for pregnancy by transrectal estrous cycle category (analyzed by Chi Square), ultrasonography using a 5-MHz transducer (Aloka, BW at the start of breeding, and pregnancy rate for Wallingford, CT) and hip height was measured. treatment by estrous cycle grouping are presented. In late November or early December of each year, heifers diagnosed as pregnant were divided RESULTS into their postweaning treatment groups to allow for different levels of supplemental feeding through the winter as described previously (Roberts et al., Effect of Estrous Cycle Grouping 2016). For the majority of the study, pasture for- Heifers that were nonpubertal at the start age was readily available for winter grazing and of breeding (0 cycle group) were born 6 d later the only additional supplemental protein provided (P < 0.01) than heifers in the 1, 2, or 3 cycle group, was alfalfa cubes or hay, depending on the year. which were 4 d younger (P < 0.01) than heifers in Supplement was fed either daily or every other day the >3 cycle group (Table 1). Birth weight decreased to achieve 1.8 or 1 kg/day offered for each con- as the number of cycles exhibited before breeding trol or restricted heifer, respectively. When pasture increased (P < 0.05, Table 2). Conversely, prewean access was limited due to snow cover, heifers were ADG and weaning weight (P < 0.01) increased provided 10.9- or 9.1-kg alfalfa hay/d for control as the number of cycles exhibited before breeding and restricted treatments, respectively. At approxi- increased (Table 1). Postwean weight gain and hip mately 2 to 4 wk before the start of calving, heif- height at 12.5 mo age were influenced by cycle num- ers were recombined and weighed. Date of calving, bers in a quadratic fashion (P < 0.03) with increas- calf birth weight, and interval from the start of ing values from 0 to 3 cycles and a decrease or no breeding to calving were recorded for each animal. change from 3 to >3 cycles (Table 1). Pregnancy rates for the second breeding season Carcass ultrasound measurements of loin were recorded for all cows nursing a calf (n = 898). area, width-to-height ratio of loin, and fat thick- ness over the loin increased with increasing num- Statistical Methods ber of cycles exhibited before breeding (P < 0.01, Data were analyzed with SAS (SAS Inst. Inc., Table 1). Intramuscular fat in the loin did not vary Cary, NC). Differences in measurements taken on (P = 0.17) by number of estrous cycles exhibited heifers and their calves due to different estrous cycle before breeding. categories were evaluated by the GLIMMIX pro- Heifer weight before breeding was influenced by cedure with a model that included random effects cycle numbers in a quadratic fashion (P < 0.02) with of year (n = 9), and fixed effects of postweaning increasing weight from 0 to 3 cycles and a plateau feeding treatment (n = 2), estrous cycle classifica- from 3 to >3 cycles (Table 1). Differences observed tion (n = 5), and interaction of feeding treatment for day of birth among the estrous cycle groupings × estrous cycle category. Interaction of feeding carried over to differences in age at the start of breed- treatment × estrous cycle category only approached ing, with 0 cycle heifers being youngest (421 d of significance (P < 0.06) in the analysis for average age), followed by heifers that exhibited either 1, 2, or daily gain during the postweaning feeding treat- 3 estrous cycles before breeding (426 d of age), which ment and was therefore removed from the model were younger (P < 0.01) than heifers exhibiting >3 Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 4 Roberts et al. Table 1. Growth, carcass characteristics, and pregnancy rate of heifers classified by the number of estrous cycles exhibited before the start of breeding Number of estrous cycles Item 0 1 2 3 > 3 SE* P value Number of heifers 395 205 211 116 249 a b b b c Julian day of birth 101 95 95 95 91 2.3 <0.001 a ab bc bc c Weight at birth, kg 35.7 34.9 34.4 34.5 33.7 0.6 <0.001 a b b bc c Weight at wean, kg 193 202 204 206 210 4.0 <0.001 a b bc bc c Gain birth to wean, kg/d 0.88 0.90 0.91 0.92 0.93 0.02 <0.001 a b bc c bc Gain 8 to 12.6 mo, kg/d 0.55 0.57 0.58 0.61 0.58 0.04 <0.002 ‡ a b b b b Hip height , cm 117.0 117.7 118.2 118.1 117.8 0.6 <0.004 ‡ 2 a b c cd d Loin muscle area , cm 52.2 53.7 56.0 57.2 58.0 1.3 <0.001 ‡ b c cd d Loin width:height 0.45 0.46 0.47 0.47 0.48 0.04 <0.001 ‡ a b c cd d Fat over loin ,mm 3.13 3.52 3.81 3.81 4.07 0.21 <0.001 || a b b bc c Weight, start of breeding, kg 307 321 321 327 329 7.5 <0.001 a bx bx by b 420-d adjusted weight, kg 311 322 321 328 326 8.2 <0.001 a b b b b Weight at pregnancy test, kg 391 397 398 403 400 10.4 0.002 a b b b c Gain 14 to 19 mo, kg/d 0.54 0.50 0.50 0.50 0.46 0.05 <0.001 ax b ay aby b Heifer first season pregnancy rate, % 84 90 88 89 94 3.5 <0.008 *Largest SE of mean. P value for the effect of estrous cycle category. Measured at 12.6 mo of age (range 330 to 432 d of age). || Weight was adjusted to 420 d of age. Trend for interaction (P = 0.058) of estrous cycle classification and postweaning feeding treatment (shown in Figure 1). a–c Means within a row without a common superscript differ (P ≤ 0.05). x,y Means within a row without a common superscript tend to differ (P ≤ 0.11). Table 2. Body weight, calving characteristics, and rebreeding of pregnant heifers classified by the number of estrous cycles exhibited before the start of first breeding Number of estrous cycles Item 0 1 2 3 >3 SE* P value Number pregnant heifers 322 176 184 103 225 a b b b ab Weight at start of calving, kg 418 425 425 430 424 12 0.032 a abx a a by Age at calving, d 720 723 722 722 727 3.3 0.019 a b b b b Days start breeding to calving 300 296 295 295 296 1.4 <0.001 a a b b b Percent calving in 21 d 49 54 60 63 60 6.0 0.033 a b b b b Weight, calves at weaning, kg 180 187 188 189 184 6.3 0.001 a bx a b by Second pregnancy rate, % 73 85 79 90 92 4.7 <0.001 *Largest SE of mean. P value for the effect of estrous cycle category. a,b Means within a row without a common superscript differ (P ≤ 0.05). x,y Means within a row without a common superscript tend to differ (P < 0.07). estrous cycles before breeding (430 d). Adjustment of which did not differ among each other (Table 1). weight to a common age at the start of breeding (420 However, average weight gain from breeding to d of age, Table 1) reduced numeric differences among pregnancy diagnosis differed (P < 0.001) due to groups and changed numeric ranking of heifers in the estrous cycle grouping, being greatest in the 0 cycle >3 cycle group from being heaviest to intermediate in group, intermediate in the 1, 2, and 3 estrous cycle weight. These adjusted weights followed a quadratic groups, and least in the >3 cycle group (Table 1). response (P < 0.02) to estrous cycle number as was Because of the greater weight gain in the 0 cycle observed for nonadjusted weights. group, magnitude of differences in body weight Heifer weight at pregnancy diagnosis at approxi- between this and the other estrus cycle groups mately 19 mo of age remained lighter (P < 0.05) for decreased compared with differences observed at the 0 cycle group than other estrous cycle groups, earlier measurements. Hip height at pregnancy Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 Onset of puberty and heifer characteristics 5 diagnosis did not differ (P = 0.48, 125.7 cm) due to estrous cycle grouping. Pregnancy rates differed (P < 0.007) by number of estrous cycles exhibited before the start of breed- ing (Table 1). Heifers that had 0 estrous cycles before breeding had lower pregnancy rates (P < 0.05) than heifers exhibiting 1 or >3 estrous cycles before breeding and tended to differ (P < 0.1) from the 2 and 3 estrous cycle groups. For heifers that became pregnant, precalving body weights were influenced by cycle numbers in a quadratic fashion (P = 0.032), where heifers in the 0 estrous cycle group weighed less than heifers exhibiting 1 to 3 estrous cycles before breeding, and weights of heifers in the >3 cycle group were not different from other groups (Table 2). Heifers in the 0 estrous cycle group had 3- to 5-d longer (P < 0.05) interval (300 ± 1 day) from the start of breeding to calving than other estrous cycle groups (Table 2). Proportion of heifers calving in the first 21 d of the calving season was greater (P < 0.05) in heifers that had two or more cycles than heifers with 0 or 1 cycle (Table 2). Birth weight of calves of heifers calving was not influenced by estrous cycle grouping (P = 0.6, 32 kg). However, calf weight at weaning was influenced by estrous cycle grouping (P = 0.001), with calves born to heifers in the 0 estrous cycle group being lighter than calves from heifers in the other groups (Table 2). Rebreeding pregnancy rates at 2 yr of age were lowest (P < 0.05) for heifers from the 0 and 2 estrous cycle groups than heifers that had 1, 3, or >3 estrous cycles before first breeding (Table 2). Effect of Feeding Level During Postweaning Figure 1. Sample distribution (A), postwean average daily gain (ADG; Development B), body weight at the start of breeding (BW; C), heifer pregnancy rate (D), and rebreeding pregnancy rate at 2 yr of age (E) for heifers clas- sified by postweaning development treatment and number of estrous Proportion of heifers in each estrous cycle clas- cycles exhibited before the start of breeding. Heifers were fed to appetite sification was influenced (P < 0.006) by feeding (Control) or were fed at 80% of that consumed by controls adjusted to a treatment during the postweaning period, with the common weight basis (Restricted) for a 140-d period from approximately 60 d after weaning to 40 ± 11 d before the start of breeding. Heifers were restricted feeding resulting in a smaller proportion classified into five groups based on the number of estrous cycles exhib- in the >3 estrous cycle group and greater propor- ited before breeding (0, 1, 2, 3, or >3). Restricted feeding resulted in a tion in the 0 cycle group (Figure 1A). Average daily smaller (P = 0.008) proportion of heifers in the >3 estrous cycle group and greater (P < 0.001) proportion in the 0 cycle group (A). Average daily gain during the postweaning feeding treatment gain during the postweaning feeding treatment differed due to interaction tended to differ due to interaction (P = 0.058) of (P = 0.058) of feeding treatment × estrous cycle classification, where the 0 feeding treatment and estrous cycle classification, estrous cycle group differed from other estrous cycle groups in control fed where the pattern of numerical differences across heifers but not restricted heifers (B). Heifer weight at the start of breeding (C) was decreased by restricted feeding (P < 0.001) and varied by estrous estrous cycle groupings was similar for both treat- cycle classification (P < 0.001). Postweaning development did not affect ments, but statistical differences between estrous pregnancy rate (D, P = 0.66) or pregnancy rate at 2 yr age (E, P = 0.19), cycle groupings only existed in control fed heifers so differences across estrous cycle grouping are same as shown in Tables 1 and 2, respectively. Positive Y error bars extend from top of each bar and not restricted heifers (Figure 1B). Differences in (B) through (E). *Denotes differences (P < 0.05) due to nutritional in BW resulting from the postweaning treat- abc treatment. Bars or estrous cycle classifications without common super - ments remained evident at the start of breeding xy scripts differ (P < 0.05). Bars or estrous cycle classifications without common superscripts differ (P < 0.11). (Figure 1C, P < 0.001) and patterns of change Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 6 Roberts et al. across the estrous cycle groupings were similar for for lower pregnancy rates at first estrus compared both feeding treatment (P = 0.4 for interaction with third estrus, magnitude of difference was of feeding treatment by estrous cycle classifica- much greater in the study by Byerley et al. (1987) tion). Neither heifer pregnancy rate (Figure 1D, than in the present study (20 vs. 5 percentage point P = 0.66) nor rebreeding rate (Figure 1E, P = 0.19) reduction for the respective studies). In addition, was influenced by postweaning feeding or interac- results from the present study do not support the tion of feeding treatment by estrous cycle grouping theory that pregnancy rate was improved in heif- (P > 0.26). Thus, differences in pregnancy rates due ers expressing >1 estrous cycle before the start of to the main effect of estrous cycle classification are breeding. The discrepancies in the results obtained as indicated in Tables 1 and 2. by Byerley et al. (1987) and the present study are likely due to differences in experimental design and may also reflect genetic changes in age of puberty DISCUSSION in heifers over time, as suggested in the reviews by Results from this study demonstrate the number Funston et al. (2012a) and Endecott et al. (2013). In of estrous cycles heifers exhibit before the start of the study by Byerley et al. (1987), insemination date breeding correspond to biological differences evi- corresponded to when heifers first expressed estrus, dent at time of birth, and throughout preweaning whereas initiation date of breeding remained con- and postweaning development. Although classifi- stant in the present study. Heifers inseminated at cation by 21-d intervals may not result in the most first estrus were approximately 11 mo old at the time descript distinction between adjacent groups (ani- of breeding in the study by Byerley et al. (1987), mals at the beginning of one 21-d period are very whereas breeding was not initiated until approxi- close to animals at the end of the adjacent period), mately 14 mo of age in the present study, which is a general conclusion from the data may be the dif- more representative of current industry practices. ferences observed are consistent with a continuum The importance of differences in the age of breed- in maturation rate across the population that also ing between these two studies was alluded to by reflects biological differences in size at maturity. Byerley et al. (1987) where increased age resulted Heifers that reached puberty earlier in life, and thus in increased pregnancy rates for heifers insemi- exhibited a greater number of estrous cycles before nated at first estrus, but not in heifers inseminated breeding, were born earlier and exhibited greater on their third estrus. Another difference between growth rates from birth to weaning. Statistical sep- the two studies is that heifers were only provided aration of the measurements analyzed provides one opportunity to conceive in Byerley et al. (1987), support of three distinct groupings: animals that whereas multiple opportunities for conception were did not exhibit estrus before the start of breeding, possible in the present study. animals exhibiting 1 to 3 estrous cycles, and those The observation from the present study that exhibiting >3 estrous cycles. As would be expected, heifers exhibiting only 1 estrous cycle before breed- the group exhibiting the greatest number of estrous ing had a lower proportion calving in the first 21 d cycles before breeding exhibited characteristics than groups exhibiting >1 cycle could be indicative indicative of earlier maturation of skeletal (hip of improved performance in heifers exhibiting more height), muscle (loin development), fat deposition, than one estrous cycle before breeding. However, and an earlier plateau in growth rate compared average interval between the start of breeding and with heifers exhibiting fewer or no estrous cycles calving, and weight of calves at weaning (unad- before the start of breeding. Heifers that did not justed for age) did not differ among groups that exhibit estrus before breeding were heavier at birth, exhibited one or more cycles before the start of with slower growth rates up to breeding, but greater breeding. growth rate at later stages of development, indica- Results of the present study indicate that second tive of slower growing, later maturing animals. breeding season pregnancy rates were influenced by In the present study, heifers that had not exhib- estrous cycle category. However, results were incon- ited estrus before breeding would have their first sistent with a hypothesis of a linear relationship opportunity to conceive on their pubertal estrus. between rebreeding pregnancy rate and number of Heifers expressing 2 estrous cycles before breeding cycles exhibited prior to first breeding. Results sup- would have their first opportunity to conceive on port a qualitative response, where greater rebreed- their third estrus. These groups of heifers are com- ing performance was observed in animals that had parable to the treatment groups of Byerley et al. expressed three or more estrous cycles before the (1987). Although both studies provide evidence start of first breeding. Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 Onset of puberty and heifer characteristics 7 Rebreeding performance can be affected by age. clear if the lower rebreeding pregnancy rates were Impact of age appears to be a function of when an associated with altered timing of puberty through animal was born (i.e., early vs. later in the calving management strategies in the postweaning period, season), which will translate into differences in age or from providing less winter supplementation, or at the start of breeding and may also carry over to the combination of both. Funston and Deutscher age at first calving. Age differences at calving will (2004) found no difference in rebreeding rates of also be influenced by differences in when an ani- heifers developed at two rates of postweaning gain mal conceives (Lesmeister et al., 1973; Funston very similar to those in the present study. However, et al., 2012b; Cushman et al., 2013). In the present all heifers were treated similarly subsequent to the study, heifers in the >3 estrous cycle group had the postweaning phase in the Funston and Deutscher numerically highest second season pregnancy rate. study. Thus, it was speculated less winter sup- These animals were born earlier and thus older at plement prior to first calving contributed to the the start of breeding than other heifers. These dif- decreased rebreeding in the population evaluated ferences carried over to this group being oldest at in the present study, and not the dietary differences first calving. prior to first breeding (Roberts et al., 2016). The nutritional treatments in this study resulted In the present study, different breeding proto- in differences in weight at the start of breeding and cols were implemented across years. Differences in puberty attainment, as reflected by the altered pro- breeding protocols, such as breeding season length portion of heifers in the 0 and >3 estrous cycle and inclusion of the CIDR in the estrous synchro- groupings (Figure 1A). However, a definitive impact nization protocol, could have influenced results con- of nutritional treatment on heifer pregnancy rate cerning breeding performance of animals classified was not evident. These observations are consistent into the different estrous cycle categories. However, with previous analyses on this population with dif- insights into impacts of differences in breeding ferent statistical models (Roberts et al., 2009, 2016, protocol on the results were not evaluated because 2017). Although studies from several decades ago breeding protocols were confounded by year. found that postweaning nutritional alterations in With exception to information discussed in puberty rates at the start of breeding were associ- the three preceding paragraphs, variation in the ated with altered heifer pregnancy rate, association measurements observed across estrous cycle cat- between proportion pubertal at the start of breed- egories would be expected to result from inherent ing and pregnancy rate has become less evident genetic variation in traits influencing maturation over time (Funston et al., 2012a; Endecott et al., rate and size at maturity. For example, differences 2013). Differences in measurements up to weaning in day of birth are likely the culmination of traits observed in the present study support previous find- associated with time of conception and gestation ings that early developmental differences can have length. Differences in weight at birth would also greater impact on subsequent reproductive perfor- be influenced by gestation length, in addition to mance than postweaning growth rate, as discussed variation in intrauterine growth rate, which will be previously (Roberts et al., 2009). correlated with subsequent growth rate and mature With the statistical model used in the present size. Current management strategies for heifer study, rebreeding performance did not differ signif- development during the postweaning period are icantly due to nutritional treatments. These results to provide sufficient nutritional input to promote differ from previous results obtained using a statis- earlier puberty with the intent to improve heifer tical model that did not account for pubertal status, pregnancy rate. This approach may be counter-pro- where rebreeding pregnancy rates were reduced by ductive over the long term by masking genetic the restricted level of feeding (Roberts et al., 2016). differences that could contribute to improved effi- Although interaction of nutritional treatment and ciency through greater retention over time with less estrous cycle classification did not (P = 0.26) affect nutritional inputs. Although selecting replacement rebreeding performance in the present study, visual heifers based on the number of estrous cycles exhib- appraisal of data in Figure 1D indicates numeric ited before breeding may not be practical, results decreases for restricted animals that exhibited <3 from this study provide precedent to select heifers estrous cycles before first breeding. An important based on differences in birthdate, birth weight, and consideration for results on rebreeding perfor- preweaning growth rate. Initial application of this mance is that nutritional treatments were imposed approach may be best implemented by selection at two time points: postweaning to prebreeding against animals with characteristics exhibited by and the last trimester of pregnancy. Thus, it is not the 0 cycle group, and exposing more females to Translate basic science to industry innovation Downloaded from https://academic.oup.com/tas/advance-article-abstract/doi/10.1093/tas/txy118/5200731 by Ed 'DeepDyve' Gillespie user on 27 November 2018 8 Roberts et al. Endecott, R. L., R. N. Funston, J. T. Mulliniks, and A. first breeding than needed to maintain static female J. Roberts. 2013. Joint alpharma-beef species sympo- inventory. Additional selection could be imposed sium: implications of beef heifer development systems by implementing a relatively short breeding season and lifetime productivity. J. Anim. Sci. 91:1329–1335. or fetal aging during pregnancy diagnosis to ensure doi:10.2527/jas.2012-5704 retention of heifers that conceived early. Funston, R. N., and G. H. Deutscher. 2004. Comparison of Results of the present study indicate that target breeding weight and breeding date for replace- second breeding season pregnancy rates were ment beef heifers and effects on subsequent reproduc- tion and calf performance. J. Anim. Sci. 82:3094–3099. influenced by estrous cycle category. However, doi:10.2527/2004.82103094x results were inconsistent with a hypothesis of Funston, R. N., J. L. Martin, D. M. Larson, and A. J. Roberts. a linear relationship between rebreeding preg- 2012a. Physiology and endocrinology symposium: nutri- nancy rate and number of cycles exhibited prior tional aspects of developing replacement heifers. J. Anim. to first breeding. Results support a qualitative Sci. 90:1166–1171. doi:10.2527/jas.2011-4569 response, where greater rebreeding performance Funston, R. N., J. A. Musgrave, T. L. Meyer, and D. M. Larson. was observed in animals that had expressed three 2012b. Effect of calving distribution on beef cattle prog- eny performance. J. Anim. Sci. 90:5118–5121. doi:10.2527/ or more estrous cycles before the start of first jas.2012-5263 breeding. Lesmeister, J. L., P. J. Burfening, and R. L. Blackwell. 1973. Date of first calving in beef cows and subsequent ACKNOWLEDGMENTS calf production. J. Anim. Sci. 36:1–6. doi:10.2527/ jas1973.3611 USDA–ARS is an equal opportunity/affirma- Newman, S., M. D. MacNeil, W. L. Reynolds, B. W. Knapp, tive action employer and all agency services are and J. J. Urick. 1993. Fixed effects in the formation of a available without discrimination. Mention of a pro- composite line of beef cattle: I. Experimental design and prietary product does not constitute a guarantee or reproductive performance. J. Anim. Sci. 71:2026–2032. warranty of the product by USDA or us and does doi:10.2527/1993.7182026x not imply its approval to the exclusion of other Roberts, A. J., R. N. Funston, E. E. Grings, and M. K. Petersen. 2016. Triennial reproduction symposium: beef heifer devel- products that may also be suitable. We gratefully opment and lifetime productivity in rangeland-based pro- acknowledge Brooke Shipp, USDA, ARS, Miles duction systems. J. Anim. Sci. 94:2705–2715. doi:10.2527/ City, MT for technical assistance in conducting this jas.2016-0435 study and Dr. Tom Geary, USDA, ARS, Miles City, Roberts, A. J., T. W. Geary, E. E. Grings, R. C. Waterman, MT for analysis of progesterone samples. and M. D. MacNeil. 2009. Reproductive performance of heifers offered ad libitum or restricted access to feed for a LITERATURE CITED one hundred forty-day period after weaning. J. Anim. Sci. 87:3043–3052. doi:10.2527/jas.2008-1476 Bellows, R. A., R. B. Staigmiller, J. M. Wilson, D. A. Phelps, and Roberts, A. J., A. Gomes da Silva, A. F. Summers, T. W. Geary, A. Darling. 1991. Use of bovine FSH for superovulation and R. N. Funston. 2017. Developmental and reproduc- and embryo production in beef heifers. Theriogenology. tive characteristics of beef heifers classified by pubertal 35:1069–1082. doi:10.1016/0093-691X(91)90355-H status at time of first breeding. J. Anim. Sci. 95:5629–5636. Byerley, D. J., R. B. Staigmiller, J. G. Berardinelli, and R. doi:10.2527/jas2017.1873 E. Short. 1987. Pregnancy rates of beef heifers bred Roberts, A. J., S. I. Paisley, T. W. Geary, E. E. Grings, R. either on puberal or third estrus. J. Anim. Sci. 65:645–650. C. Waterman, and M. D. MacNeil. 2007. Effects of doi:10.2527/jas1987.653645x restricted feeding of beef heifers during the postwean- Cushman, R. A., L. K. Kill, R. N. Funston, E. M. Mousel, and ing period on growth, efficiency, and ultrasound carcass G. A. Perry. 2013. Heifer calving date positively influences calf weaning weights through six parturitions. J. Anim. characteristics. J. Anim. Sci. 85:2740–2745. doi:10.2527/ Sci. 91:4486–4491. doi:10.2527/jas.2013-6465 jas.2007-0141 Translate basic science to industry innovation
Translational Animal Science – Oxford University Press
Published: Nov 23, 2018
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