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Genetic marker effects and type of inheritance are estimated with poor precision when minor marker allele frequencies are low. A stable composite population (MARC II) was subjected to marker assisted selection for 2 yr to equalize CSN1S1and TGgenetic marker frequencies to evaluate the epistatic and pleiotropic effects of these markers on BW, reproduction, and first calf performance traits in replacement beef females (n= 171) managed under 2 postweaning development protocols. Traits evaluated on the heifers were birth BW, weaning BW, 11-mo BW, 12-mo BW, 13-mo BW, first breeding season pregnancy evaluation BW, first calving season BW, 11-mo puberty, 12-mo puberty, 13-mo puberty, first breeding season pregnancy, and first calf weaning rate. Additionally, heifer's first calf performance traits of ordinal calving date, first calf birth BW, and first calf weaning BW (with and without age adjustment) were analyzed. Selection to increase minor allele frequencies and balanced sampling across genotype classes enhanced the ability to detect all genetic effects except dominance × dominance epistasis. The CSN1S1× TGgenotype effect was significant (P< 0.05) for 11-mo BW and 12-mo BW and tended to be significant (P= 0.08) for 13-mo BW. Consistently, for all 3 traits, the most significant effect among epistatic CSN1S1× TGgenotype effects was the CSN1S1additive effect, with the G allele decreasing BW. There were no associations between CSN1S1× TGgenotype and fertility related traits (P≥ 0.46) in this study. Additionally, there were no CSN1S1× TGgenotype associations with first progeny performance traits (P≥ 0.14). The large effect of the CSN1S1additive × TGadditive interaction on first calf weaning BW was imprecisely estimated, which may warrant further investigation.

The preweaning litter environment of gilts can affect subsequent development. In a recent experiment designed to test the effects of diet on gilt development, litter-of-origin traits including individual birth weights, immunocrits (a measure of colostrum intake), sow parity, number weaned, and individual weaning weights were collected for approximately 1,200 gilts that were progeny of approximately 300 sows. Subsequently, BW, LM area, and backfat were measured at 100 d of age and at 28-d intervals until slaughter (260 d of age). From 160 d of age to slaughter, gilts were observed daily for estrus. At slaughter, the reproductive tract and 1 mammary gland were recovered. The reproductive tract was classified as cyclic or prepubertal; the number of corpora lutea was counted. Uterine horn lengths and ovarian dimensions were measured. Uterus and ovary samples from every 10th gilt were prepared for histological evaluation of uterine gland development and follicle counts, respectively. Mammary gland tissue protein and fat were assayed. Day of the estrous cycle at slaughter was calculated using the first day of the most recent standing estrus (d 0) recorded previous to slaughter. Each gilt development trait was analyzed for association with each litter-of-origin trait, after adjusting for dietary treatment effects. Uterine length, ovarian dimensions, mammary gland protein and fat, and uterine gland development were also adjusted for day of the estrous cycle at slaughter. All litter-of-origin traits were associated (P< 0.05) with growth traits. Top-down (backward elimination) multiple regression analysis indicated that BW and LM accretion in gilts was positively associated with immunocrit (P< 0.01), birth weight (P< 0.01), preweaning growth rate (P< 0.01), and parity (P< 0.01). Backfat accretion was positively associated with preweaning growth rate (P< 0.01), number weaned (P< 0.05), and parity (P< 0.05). Age at puberty was associated with birth weight (positive; P< 0.01) and preweaning growth rate (negative; P< 0.01). Total uterine length was positively associated with only birth weights (P< 0.05). Mammary gland protein was negatively associated with preweaning growth (P< 0.01). Mammary gland fat was positively associated with birth weight and number of piglets weaned (P> 0.05). These results indicate that colostrum consumption, birth weights, preweaning growth rate, number weaned, and parity are associated with gilt development traits during later life.

Peripubertal caloric restriction increases primordial follicle numbers at breeding, which may improve reproductive potential. Our hypothesis was that feed restriction was changing primordial follicle number through stimulation of follicle formation via leptin, roundabout axon guidance receptor, homolog 4 (ROBO4), or SLIT2or through inhibition of follicle activation via anti-Müllerian hormone (AMH). Heifers (n= 30) were fed a ration consisting of 30% alfalfa hay, 69.8% corn silage, and 0.2% salt as DM. Heifers received the control diet for 42 d before an initial 6 heifers were ovariectomized at 8 mo of age. The remaining 24 heifers were divided into 2 treatment groups. Controls were offered 97.9 g DM/kg BW0.75over the entire feeding period. Stair-step heifers received 67.4 g DM/kg BW0.75for 84 d. Following the 84-d restriction, heifers were stepped up to receive 118.9 g DM/kg BW0.75over a 15-d period and were held at this feeding level 68 d. At the end of the feed restriction (11 mo of age), ovaries were collected from 6 heifers per treatment, and at the end of the refeeding period (13 mo of age), ovaries were collected from 6 heifers per treatment. Plasma leptin concentrations were greater in control heifers than in stair-step heifers at 11 mo of age (P< 0.0001). In histological sections, stair-step heifers had more primordial follicles (P= 0.03) than control heifers at 13 mo of age. There was no difference in secondary or antral follicle numbers between dietary treatment groups or ages. Relative abundance of ROBO4mRNA in ovarian cortex of control heifers was greater at 13 mo than at 11 mo or before feed restriction (8 mo; P= 0.01). Relative abundance of ROBO4mRNA in stair-step heifers at 13 mo was greater than before feed restriction (P= 0.02) and at 11 mo did not differ from 8 or 13 mo (P= 0.70). Relative abundance of SLIT2mRNA in the ovarian cortex followed a similar pattern, being greater in stair-step heifers at 11 mo compared with control heifers (P= 0.001). At 13 mo, SLIT2mRNA did not differ between treatments (P= 0.30). Abundance of AMHmRNA in the ovarian cortex did not change due to dietary treatment or age (P> 0.10). In conclusion, developing heifers on a stair-step compensatory growth scheme resulted in larger ovarian reserve before the onset of breeding, which may have beneficial effects on increasing reproductive lifespan.

The objective of this study was to determine the effect of ad libitum feeding diets differing in standard ileal digestible (SID) lysine and ME concentrations that bracket those fed to developing gilts in U.S. commercial settings. Average SID lysine and ME concentrations in diets currently fed to developing gilts were obtained from a poll of the U.S. commercial swine industry. Crossbred Large White × Landrace gilts (n= 1,221), housed in groups, were randomly allotted to 6 corn-soybean diets in a 2 × 3 factorial arrangement formulated to provided 2 SID lysine and 3 ME concentrations. Gilts received grower diets formulated to provide 1.02% (control = survey average) or 0.86% (control minus 15%) SID lysine and 2.94, 3.25, or 3.57 (survey average ME ± 10%) Mcal of ME/kg from 100 d of age until approximately 90 kg BW. Then, gilts were fed finisher diet containing 0.85% (control = survey average) or 0.73% (control minus 15%) SID lysine and 2.94, 3.26, or 3.59 (control ± 10%) Mcal of ME/kg until 260 d of age. Gilts were weighed, and backfat thickness and loin muscle area were recorded at the beginning of the trial and then every 28 d. Starting at 160 d of age, gilts were exposed daily to vasectomized boars and observed for behavioral estrus. At approximately 260 d of age, gilts were slaughtered and their reproductive tract was collected. Each reproductive tract was examined to determine whether the gilt was cyclic, the stage of estrus cycle, ovulation rate, and uterine length. Data were evaluated for normality and analyzed using mixed model methods. Average age at puberty was 193 d of age with a range from 160 to 265 d. When all gilts on trial at 160 d of age were included in the analysis, 91.0% reached puberty as determine by observation of standing estrus. Differences between dietary treatments on age at puberty or measurements of the reproductive tract were not detected. Growth rates to 160 d were not limiting for attainment of puberty in response to daily boar stimulation from 160 d.

The use of genetic markers to aid in selection decisions to improve carcass and growth characteristics is of great interest to the beef industry. However, it is important to examine potential antagonistic interactions with fertility in cows before widespread application of marker-assisted selection. The objective of the current experiment was to examine the influence of 2 commercially available markers currently in use for improving carcass traits, the myostatin (MSTN) F94L and μ-calpain (CAPN1) 316 and 4751 polymorphisms, on heifer development and reproductive performance. In Exp. 1, beef heifers (n= 146) were evaluated for growth and reproductive traits over a 3-yr period to determine if these polymorphisms influenced reproductive performance. In Exp. 2, heifers representing the 2 homozygous genotypes for the MSTNF94L polymorphism were slaughtered on d 4 of the estrous cycle and reproductive tracts were collected for morphological examination. In Exp. 1, there was a tendency (P= 0.06) for birth BW to be affected by MSTNwith the Leu allele increasing birth BW in an additive fashion. Additionally, MSTNsignificantly affected the proportion of pubertal heifers by the start of the breeding season (P< 0.05) with the Leu allele additively decreasing the proportion pubertal; however, this did not result in a delay in conception or a decrease in pregnancy rates during the first breeding season (P> 0.15). The GT haplotype of CAPN1, which was previously associated with decreased meat tenderness, was associated with an additive decrease in birth BW of the first calf born to these heifers (P< 0.05). In Exp. 2, there were no differences between the MSTNgenotypes for gross or histological morphology of the anterior pituitary, uterus, or ovaries (P> 0.05). From these results, we concluded that the MSTNF94L and CAPN1polymorphisms can be used to improve carcass traits without compromising fertility in beef heifers. The influence of these markers on cow performance and herd life remains to be determined. While the delay in puberty associated with the MSTNF94L polymorphism did not negatively impact reproductive performance in heifers, caution should be used when combining this marker with other markers for growth or carcass traits until the potential interactions are more clearly understood.

Replacing cows in the herd is second only to nutrition as the single greatest input cost in cow/calf beef production. The increased availability of cereal grains for feeding livestock has allowed replacement heifers to enter the production system at younger ages. Many heifer development programs feed to ensure heifers reach puberty before the time that they are mated to calve at 2 yr of age. Nutrition level during development has been associated with altered milk production and stayability. We hypothesized that heifers exposed to a lower nutrition level during the peripubertal period would have less methylation of the DNA in the mammary gland and ovarian cortex. We also hypothesized that the ovarian reserve would decrease in heifers fed for rapid growth compared to heifers fed for slow growth during puberty. At 257 ± 1 d of age, heifers in the Stair-Step treatment (n= 6) received 157 kcal ME/BW kg0.75for 84 d and heifers in the Conventional treatment (n= 6) were offered 228 kcal ME/BW kg0.75. At d 84, heifers were fed for an additional 83 d. Stair-Step heifers were offered 277 kcal ME/BW kg0.75, and heifers on the Conventional treatment received 228 kcal ME/BW kg0.75. Mammary weights (P= 0.43), capillary area density (P= 0.74), and capillary surface density (P= 0.18) did not differ between treatments and neither did alveolar number (P= 0.55) and alveolar density (P= 0.49). Reproductive tract weights (P= 0.69) and ovarian weight (P= 0.68) and ovarian size (P> 0.75) did not differ between treatments. In histological sections, Stair-Step heifers had more primordial follicles than Conventional heifers (P= 0.02), but primary (P= 0.59) and secondary (P= 0.15) follicles did not differ. Global methylation of parenchymal tissue (P= 0.82), mammary fat pad (P= 0.45), and ovarian cortex (P= 0.14) did not differ between treatments. Anterior pituitary weight did not differ between treatments (P= 0.16). Our hypothesis that modifying peripubertal nutrition modifies global methylation of the mammary and ovary is not supported; however, our hypothesis that it modifies the ovarian reserve is supported.

Direct selection for uterine capacity (UC) increased the number of live pigs born. A method to indirectly estimate UC in developing gilts is needed for this trait to be incorporated into commercial selection strategies. We tested the hypothesis that selection for UC alters phenotypic characteristics of the reproductive tract of prepubertal gilts and that these changes could be estimated in live animals using transrectal ultrasound (TRU). Gilts from lines selected for UC and a randomly selected control (CO) line were submitted for TRU at 130, 150, or 170 d of age and harvested 24 h later (n= 10 gilts/line per age). Diameter of the uterine horn was measured (2 to 4 measurements per animal) at TRU. At harvest, measurements of the ovary (height, width, length, weight, and number of visible follicles >1 mm) and uterine horn (weight, length, diameter, and endometrial diameter) were taken. There was no line × age interaction for any of the traits. All ovarian traits increased (P< 0.03) with age. Weight and length of the uterine horn was not different at 130 or 150 d but were increased (P< 0.01) at 170 d of age. Diameter of the uterine horn tended (P= 0.06) to be increased at 170 d compared with 130 or 150 d, but age did not affect (P= 0.38) endometrial diameter. Ovarian weight and width were increased (P< 0.01) and ovarian length and height tended (P= 0.07) to be greater for UC than CO gilts, but the number of visible follicles did not differ. The UC gilts had increased (P< 0.02) weight of uterine horns, which tended (P= 0.09) to be longer than in the CO gilts. Diameter of the uterine horn and the endometrium were greater (P< 0.01) for UC gilts than for CO gilts. Uterine horn diameter measured with TRU was not affected by age or line and was not highly correlated with any of the measured traits. Selection for increased UC results in larger ovaries and uterine horns, but TRU was not useful for estimating these traits in gilts of the age studied.

Programs for developing replacement heifers are designed for heifers to calve at 2 yr of age and to extend their stayability in the herd and minimize feed cost. The experimental objective was to determine whether developing prepubertal heifers on less dietary energy and to a BW of 55% rather than 65% of mature BW at 14 mo of age would compromise ovarian development and reduce fertility. In a 3-yr study, 8-mo-old Angus (n = 60/yr) and composite MARC II (n = 60/yr) heifers were assigned equally by age, BW, and breed to receive either a low (LG) or high (HG) BW gain diet fed to achieve an ADG of either 0.45 or 0.8 kg/d from 8 to 15 mo of age, including the first 21 d of breeding, and then transferred to pasture. At 14 mo, heifers were housed with fertile bulls for 47 d. Estrus was monitored for 21 d. Within 12 h after detection of estrus, ovarian length and height, preovulatory follicle diam., and antral follicle count (AFC) were measured by transrectal ultrasonography. Corpus luteum (CL) volume and plasma progesterone concentration were measured 5 to 15 d after estrus. Data were analyzed by ANOVA with treatment, breed, and year and their 2-way interactions as independent variables. At breeding, HG heifers were heavier than LG heifers (419.9 vs. 361.8 ± 7.5 kg; P < 0.01); ADG for the treatment period was 0.79 vs. 0.47 ± 0.04 kg/d (P < 0.01), respectively. In 2010 and 2011, 97.2% of heifers were cyclic by 21 d of breeding. Size of the ovary, preovulatory follicle, CL, and AFC did not differ between HG and LG, but preovulatory follicle diam. and ovarian length were greater (P ≤ 0.05) for MARC II vs. Angus heifers. Progesterone concentrations were less for LG vs. HG heifers (P ≤ 0.02), whereas CL volume was not affected by treatment or breed but was correlated positively with preovulatory follicle size (P < 0.01). Total AFC ranged from 5 to 49 and was correlated positively with ovarian volume but was not associated with fertility. A greater proportion of HG vs. LG heifers conceived within the first 21 d of the breeding period (64.4% vs. 49.2% ± 3.8%, respectively; P < 0.01), but overall pregnancy rate was not affected by treatment (83.0% vs. 77.7% ± 3.1%, respectively; P > 0.10). Pregnancy rate was 10% less (P < 0.01) for Angus vs. MARC II heifers. Developing beef heifers at a lesser ADG to a lighter BW (55% vs. 64% of mature BW) at breeding did not influence postweaning ovarian development or AFC or compromise pregnancy rate during the 47-d breeding period.

Longevity and lifetime productivity are important factors influencing profitability for the cow-calf producer. Heifers that conceive earlier in the breeding season will calve earlier in the calving season and have a longer interval to rebreeding. Calves born earlier in the calving season will also be older and heavier at weaning. Longevity data were collected on 2,195 heifers from producers in South Dakota Integrated Resource Management groups. Longevity and weaning weight data were collected on 16,549 individual heifers at the U.S. Meat Animal Research Center (USMARC). Data were limited to heifers that conceived during their first breeding season. Heifers were grouped into 21-d calving periods. Heifers were determined to have left the herd when they were diagnosed not pregnant at the end of the breeding season. Heifers that left the herd for reasons other than reproductive failure were censored from the data. Heifers that calved with their first calf during the first 21-d period of the calving season had increased (P < 0.01) longevity compared with heifers that calved in the second 21-d period, or later. Average longevity for South Dakota heifers that calved in the first or later period was 5.1 ± 0.1 and 3.9 ± 0.1 yr, respectively. Average longevity for USMARC heifers that calved in the first, second, or third period was 8.2 ± 0.3, 7.6 ± 0.5, and 7.2 ± 0.1 yr, respectively. Calving period as a heifer influenced (P < 0.01) unadjusted weaning BW of the first 6 calves. Estimated postpartum interval to conception as a 2-yr-old cow was greater for females that calved in the first period as heifers but did not differ between heifer calving periods in subsequent calving seasons. In summary, heifers that calved early in the calving season with their first calf had increased longevity and kilograms weaned, compared with heifers that calved later in the calving season.