Effect of reproductive management programs that prioritized artificial insemination at detected estrus or timed artificial insemination on the reproductive performance of primiparous Holstein cows of different genetic merit for fertility.

Our objective was to compare reproductive outcomes of primiparous lactating Holstein cows of different genetic merit for fertility submitted for insemination with management programs that prioritized artificial insemination (AI) at detected estrus (AIE) or timed AI (TAI). Moreover, we aimed to determine whether subgroups of cows with different fertility potential would present a distinct response to the reproductive management strategies compared. Lactating primiparous Holstein cows (n = 6 commercial farms) were stratified into high (Hi-Fert), medium (Med-Fert), and low (Lo-Fert) genetic fertility groups (FG) based on a Reproduction Index value calculated from multiple genomic-enhanced predicted transmitting abilities. Within herd and FG, cows were randomly assigned either to a program that prioritized TAI and had an extended voluntary waiting period (P-TAI; n = 1,338) or another that prioritized AIE (P-AIE; n = 1,416) and used TAI for cows, not AIE. Cows in P-TAI received first service by TAI at 84 ± 3 d in milk (DIM) after a Double-Ovsynch protocol, were AIE if detected in estrus after a previous AI, and received TAI after an Ovsynch-56 protocol at 35 ± 3 d after a previous AI if a corpus luteum (CL) was visualized at nonpregnancy diagnosis (NPD) 32 ± 3 d after AI. Cows with no CL visualized at NPD received TAI at 42 ± 3 d after AI after an Ovsynch-56 protocol with progesterone supplementation (P4-Ovsynch). Cows in P-AIE were eligible for AIE after a PGF2α treatment at 53 ± 3 DIM and after a previous AI. Cows not AIE by 74 ± 3 DIM or by NPD 32 ± 3 d after AI received P4-Ovsynch for TAI at 74 ± 3 DIM or 42 ± 3 d after AI. Binary data were analyzed with logistic regression, count data with Poisson regression, continuous data by ANOVA, and time to event data by Cox's proportional hazard regression. Pregnancy per AI (P/AI) to first service was greater for cows in the Hi-Fert (59.8%) than the Med-Fert (53.6%) and Lo-Fert (47.7%) groups, and for the P-TAI (58.7%) than the P-AIE (48.7%) treatment. Overall, P/AI for all second and subsequent AI combined did not differ by treatment (P-TAI = 45.2%; P-AIE = 44.5%) or FG (Hi-Fert = 46.1%; Med-Fert = 46.0%; Lo-Fert = 42.4%). The hazard of pregnancy after calving was greater for the P-AIE than the P-TAI treatment [hazard ratio (HR) = 1.27, 95% CI: 1.17 to 1.37)], and for the Hi-Fert than the Med-Fert (HR = 1.16, 95% CI: 1.05 to 1.28) and Lo-Fert (HR = 1.34, 95% CI: 1.20 to 1.49) groups. More cows in the Hi-Fert (91.2%) than the Med-Fert (88.4%) and Lo-Fert (85.8%) groups were pregnant at 200 DIM. Within FG, the hazard of pregnancy was greater for the P-AIE than the P-TAI treatment for the Hi-Fert (HR = 1.41, 95% CI: 1.22 to 1.64) and Med-Fert (HR = 1.28, 95% CI: 1.12 to 1.46) groups but not for the Lo-Fert group (HR = 1.13, 95% CI: 0.98 to 1.31). We conclude that primiparous Holstein cows of superior genetic merit for fertility had better reproductive performance than cows of inferior genetic merit for fertility, regardless of the type of reproductive management used. In addition, the effect of programs that prioritized AIE or TAI on reproductive performance for cows of superior or inferior genetic merit for fertility depended on the outcomes evaluated. Thus, programs that prioritize AIE or TAI could be used to affect certain outcomes of reproductive performance or management.

Effect of reproductive management programs that prioritized artificial insemination at detected estrus or timed artificial insemination on the economic performance of primiparous Holstein cows of different genetic merit for fertility.

The objective of this randomized controlled experiment was to evaluate the effect of reproductive management programs that prioritized artificial insemination (AI) at detected estrus (AIE) or timed AI (TAI) during the first lactation on the economic performance of dairy cows of different genomically enhanced predicted transmitting ability for fertility. Lactating primiparous Holstein cows from 6 commercial farms were stratified into high, medium, and low fertility groups based on a reproduction index value calculated from multiple genomically enhanced predicted transmitting abilities to predict the number of days to achieve pregnancy. Within herd and fertility group, cows were randomly assigned either to a program that prioritized AIE (P-AIE; n = 1,416) and used TAI for cows not AIE for all AI services or another that prioritized TAI and had an extended voluntary waiting period for first service and prioritized TAI for second and greater AI services (P-TAI; n = 1,338). Cash flow (CF) per cow accumulated for the experimental (first) and second calving interval (CIN) and cash flow per slot per 28 mo after calving in the experimental lactation were calculated. Market and rearing heifer cost values were used for estimating CF. For cows in the high fertility group, a positive effect of delayed pregnancy on milk income during the first lactation was observed (+$248 for P-TAI) but was insufficient to generate significant differences in CF between treatments mainly because of milk income compensation in the second lactation (+$125 for P-AIE) and minor reductions in reproductive cost and gains in calf value for the P-AIE treatment. In this regard, CF for 2 CIN was greater for the P-TAI treatment by $61 and $86 for market and rearing replacement heifer cost, respectively. Similarly, CF per slot was favorable to the P-TAI treatment but only by $13 and $47 for market and rearing replacement heifer cost, respectively. For cows in the low fertility group, CF was numerically in favor of the P-AIE treatment due to a pregnancy and herd exit dynamics that resulted in gains in milk income over feed cost during the first ($29) and second ($113) lactation. Differences in CF for the 2 CIN were $58 and $47 for market or rearing heifer value, respectively, and $77 and $19 for market and rearing heifer values, respectively for the slot analysis. Differences in CF between cows of different genetic merit for fertility were consistent across treatment and estimation method. Of note, cows in the low fertility group had greater CF than cows in the high fertility group in all comparisons, ranging from $198 per cow for 2 CIN to as much as $427 per slot. For the low fertility group, greater milk production contributed directly (milk income over feed cost) and indirectly (reduced culling) to increased CF. We concluded that genetic merit for fertility and CF are associated because cows of inferior genetic potential for fertility had greater CF than cows of superior genetic for fertility despite some increased costs and reduced revenues. Also, the magnitude of the CF differences observed for cows of different genetic merit for fertility managed with the P-AIE or P-TAI program may be valuable to commercial dairy farms but did not allow to conclusively support the choice of a type of reproductive management strategy for cows of different genetic merit for fertility.

Changes in ovarian function associated with circulating concentrations of estradiol before a GnRH-induced ovulation in beef cows.

These studies were conducted to evaluate causes for differences in circulating concentrations of estradiol before a GnRH-induced ovulation. Beef cows were synchronized by an injection of GnRH on day -7 and an injection of prostaglandin F2α (PGF2α) on day 0. In experiment 1, blood samples were collected every 3 h from PGF2α on day 0 to hour 33 after PGF2α and at slaughter (hour 36 to 42; n = 10). Cows were assigned to treatment group based on circulating concentrations of estradiol (E2): HighE2 vs LowE2. At slaughter, follicular fluid (FF) and granulosa cells were collected from the dominant follicle. In experiment 2, blood samples (n = 30) were collected every 8 h from PGF2α until the dominant follicle was aspirated via ultrasound-guided follicular aspiration to collect FF and granulosa cells (hour 38 to 46). In experiment 1, HighE2 had increased abundance of 3ß-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.02), and greater concentrations of estradiol and androstenedione (P ≤ 0.02) in the FF. In experiment 2, HighE2 had increased abundance of CYP11A1, 3ß-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.03) vs either LowE2 or GnRHLowE2. There was a tendency (P = 0.07) for LH pulse frequency to be increased in both the GnRHLowE2 and HighE2 compared with LowE2. HighE2 cows experienced increas in circulating concentrations of estradiol compared with LowE2. In conclusion, animals with greater concentrations of circulating estradiol before fixed-time AI experienced an upregulation of the steroidogenic pathway during the preovulatory period.

Estimates of epistatic and pleiotropic effects of () and () genetic markers on beef heifer performance traits enhanced by selection.

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 and genetic marker frequencies to evaluate the epistatic and pleiotropic effects of these markers on BW, reproduction, and first calf performance traits in replacement beef females ( = 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 × genotype effect was significant ( < 0.05) for 11-mo BW and 12-mo BW and tended to be significant ( = 0.08) for 13-mo BW. Consistently, for all 3 traits, the most significant effect among epistatic × genotype effects was the additive effect, with the G allele decreasing BW. There were no associations between × genotype and fertility related traits ( ≥ 0.46) in this study. Additionally, there were no × genotype associations with first progeny performance traits ( ≥ 0.14). The large effect of the additive × additive interaction on first calf weaning BW was imprecisely estimated, which may warrant further investigation.

Postweaning nutritional programming of ovarian development in beef heifers.

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 (), or or through inhibition of follicle activation via anti-Müllerian hormone (). Heifers ( = 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 BW over the entire feeding period. Stair-step heifers received 67.4 g DM/kg BW for 84 d. Following the 84-d restriction, heifers were stepped up to receive 118.9 g DM/kg BW over 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 ( < 0.0001). In histological sections, stair-step heifers had more primordial follicles ( = 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 mRNA in ovarian cortex of control heifers was greater at 13 mo than at 11 mo or before feed restriction (8 mo; = 0.01). Relative abundance of mRNA in stair-step heifers at 13 mo was greater than before feed restriction ( = 0.02) and at 11 mo did not differ from 8 or 13 mo ( = 0.70). Relative abundance of mRNA in the ovarian cortex followed a similar pattern, being greater in stair-step heifers at 11 mo compared with control heifers ( = 0.001). At 13 mo, mRNA did not differ between treatments ( = 0.30). Abundance of mRNA in the ovarian cortex did not change due to dietary treatment or age ( > 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.

Genomewide association study of lung lesions in cattle using sample pooling.

Bovine respiratory disease complex (BRDC) is the most expensive disease in beef cattle in the United States costing the industry at least US$1 billion annually. Bovine respiratory disease complex causes damage to lung tissue resulting in persistent lung lesions observable at slaughter. Severe lung lesions at harvest have been associated with decreased preharvest ADG and increased clinical BRDC in the feedlot. Our objective was to identify SNP that are associated with severe lung lesions observed at harvest in feedlot cattle. We conducted a genomewide association study (GWAS) using a case-control design for severe lung lesions in fed cattle at slaughter using the Illumina Bovine HD array (approximately 770,000 SNP) and sample pooling. Lung samples were collected from 11,520 young cattle, a portion of which had not been treated with antibiotics (participating in a "natural" marketing program), at a large, commercial beef processing plant in central Nebraska. Lung samples with lesions (cases) and healthy lungs (controls) were collected when both phenotypes were in close proximity on the viscera (offal) table. We constructed 60 case and 60 control pools with 96 animals per pool. Pools were constructed by sampling sequence to ensure that case and control pool pairs were matched by proximity on the processing line. The Bovine HD array (770,000 SNP) was run on all pools. Fourteen SNP on BTA 2, 3, 4, 9, 11, 14, 15, 22, 24, and 25 were significant at the genomewide experiment-wise error rate of 5% ( ≤ 1.49 × 10). Eighty-five SNP on 28 chromosomes achieved a false discovery rate of 5% ( ≤ 5.38 × 10). Significant SNP were near (±100 kb) genes involved in tissue repair and regeneration, tumor suppression, cell proliferation, apoptosis, control of organ size, and immunity. Based on 85 significantly associated SNP in or near a collection of genes with diverse function on 28 chromosomes, we conclude that the genomic footprint of lung lesions is complex. A complex genomic footprint (genes and regulatory elements that affect the trait) is consistent with what is known about the cause of the disease: complex interactions among multiple viral and bacterial pathogens along with several environmental factors including dust, commingling, transportation, and stress. Characterization of sequence variation near significant SNP will enable accurate and cost effective genome-enhanced genetic evaluations for BRDC resistance in AI bulls and seed stock populations.

A polymorphism in myostatin influences puberty but not fertility in beef heifers, whereas µ-calpain affects first calf birth weight.

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 MSTN F94L 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 MSTN with the Leu allele increasing birth BW in an additive fashion. Additionally, MSTN significantly 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 MSTN genotypes for gross or histological morphology of the anterior pituitary, uterus, or ovaries (P > 0.05). From these results, we concluded that the MSTN F94L and CAPN1 polymorphisms 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 MSTN F94L 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.

The consequence of level of nutrition on heifer ovarian and mammary development.

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 kg0.75 for 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.

DNA polymorphisms and transcript abundance of PRKAG2 and phosphorylated AMP-activated protein kinase in the rumen are associated with gain and feed intake in beef steers.

Beef steers with variation in feed efficiency phenotypes were evaluated previously on a high-density SNP panel. Ten markers from rs110125325-rs41652818 on bovine chromosome 4 were associated with average daily gain (ADG). To identify the gene(s) in this 1.2-Mb region responsible for variation in ADG, genotyping with 157 additional markers was performed. Several markers (n = 41) were nominally associated with ADG, and three of these, including the only marker to withstand Bonferroni correction, were located within the protein kinase, AMP-activated, gamma 2 non-catalytic subunit (PRKAG2) gene. An additional population of cross-bred steers (n = 406) was genotyped for validation. One marker located within the PRKAG2 loci approached a significant association with gain. To evaluate PRKAG2 for differences in transcript abundance, we measured expression in the liver, muscle, rumen and intestine from steers (n = 32) with extreme feed efficiency phenotypes collected over two seasons. No differences in PRKAG2 transcript abundance were detected in small intestine, liver or muscle. Correlation between gene expression level of PRKAG2 in rumen and average daily feed intake (ADFI) was detected in both seasons (P < 0.05); however, the direction differed by season. Lastly, we evaluated AMP-activated protein kinase (AMPK), of which PRKAG2 is a subunit, for differences among ADG and ADFI and found that the phosphorylated form of AMPK was associated with ADFI in the rumen. These data suggest that PRKAG2 and its mature protein, AMPK, are involved in feed efficiency traits in beef steers. This is the first evidence to suggest that rumen AMPK may be contributing to ADFI in cattle.

Triennial Reproduction Symposium: limitations in uterine and conceptus physiology that lead to fetal losses.

Conceptus losses in livestock occur throughout gestation. The uterus and the embryo-placenta-fetus play interconnected roles in these losses, the details of which depend on the period of gestation and the species. Studies in sheep and pigs have indicated that the uterine glands are essential for full fertility, based on experiments where gland development was reduced through the use of exogenous hormones. In sheep and cattle, normally the uterus is well able to support more than a single fetus although these species differ in the consequences of multiple births. When 2 conceptuses are present, the placentas of cattle often anastomose, putting 1 fetus at risk if the other is lost. One likely reason this does not occur in sheep is because sheep embryos undergo intrauterine migration, similar to pigs. In pigs, the relatively equidistant separation of conceptuses is likely to be essential for optimizing conceptus survival as is the simultaneous and uniform elongation of blastocysts that occurs during the time of maternal recognition of pregnancy. Other studies in pigs have indicated that the size of the uterus influences litter size and therefore fetal losses. In response to crowded intrauterine conditions in the pig, increased conceptus losses begin to occur between d 30 and 40 of pregnancy, and further losses occur sporadically during later gestation. There is evidence that improved fetal erythropoiesis can reduce these losses. Other studies indicated that profound changes in placental development occurred under crowded intrauterine conditions that may contribute to losses during late gestation. Reductions in placental stroma formation may compromise the ability of the pig placenta to adapt to reduced uterine space. Consistent with this, both hyaluronan and hyaluronidase activity are decreased in the placentas of small compared with large fetuses. These results indicate that improvements in placental stroma formation could improve placental ability to compensate for reduced intrauterine space, resulting in increased placental function and reduced fetal losses during late gestation.