Influence of preovulatory estradiol treatment on the maintenance of pregnancy in beef cattle receiving in vivo produced embryos

This experiment was designed to determine the role of preovulatory estradiol in pregnancy retention after embryo transfer (ET). Cows were synchronized with the 7-d CO-Synch + CIDR® protocol. On d0 (d-2 =CIDR® removal), cows were grouped by estrual status (estrual [Positive Control] and nonestrual), and nonestrual cows were administered Gonadotropin Releasing Hormone (GnRH) and randomly assigned to either no treatment (Negative Control) or Estradiol (0.1 mg estradiol 17-β IM). All cows received an embryo on d7. Pregnancy status was retrospectively classified on d56, 30, 24, and 19 by either ultrasonography, plasma pregnancy-associated glycoproteins analysis (PAGs), expression of interferon-stimulated genes, plasma progesterone (P4) concentrations, or a combination of the factors. There was no difference in estradiol concentrations on day 0 h 0 (P > 0.16). At day 0 h 2, Estradiol cows (15.7 ± 0.25 pg/mL) had elevated (P < 0.001) estradiol compared with Positive Controls (3.4 ± 0.26 pg/mL) or Negative Controls (4.3 ± 0.25 pg/mL). On d19, pregnancy rates did not differ (P = 0.14) among treatments. On d24, Positive Controls (47%) had greater (P < 0.01) pregnancy rates than Negative Controls (32%); Estradiol cows were intermediate (40%). There was no difference (P = 0.38) in pregnancy rates between Positive Control (41%) and Estradiol (36%) cows on d30, but Negative Control (27%) cows had (P = 0.01) or tended (P = 0.08) to have decreased pregnancy rates, respectively. Thus, preovulatory estradiol may elicit an effect on early uterine attachment or alter histotroph components, consequently improving pregnancy maintenance through d30.

Effect of supplemental trace minerals on standard and novel measures of bull fertility

Two studies were conducted to evaluate the effects of trace mineral supplementation on traditional and novel measures of bull fertility. In Experiment 1, 37 mature bulls received one of three dietary supplements daily for 71 d: 1) Supplement without Cu, Zn, and Mn (CON); 2) Supplement with Cu, Zn, and Mn sulfate (SULF); and 3) Supplement with basic Cu chloride, and Zn and Mn hydroxychloride (CHLR). In Experiment 2, 128 Angus or Angus-Hereford bull calves were maintained on a growing diet for 75 d (year 1) or 119 d (year 2) in Calan gate equipped pens without mineral supplementation. Bulls (n = 32 head/treatment) received one of four trace mineral supplements daily for 84 d: 1) Zn with no Cu (ZN), 2) Cu with no Zn (CU), 3) Cu and Zn (ZNCU), or 4) no Cu or Zn (CON). Bull fertility measures included a breeding soundness evaluation (BSE) and novel fertility measures conducted using flow cytometry. In mature bulls, final liver Zn concentration was positively correlated (P = 0.02) with sperm concentration (r = 0.31) and tended (P = 0.06) to be negatively correlated with acrosome damage (r = -0.39). Peripubertal bulls receiving ZNCU had greater ADG than bulls in the CU group (P = 0.05). Each BSE and novel fertility component improved from Day 0-84 in peripubertal bulls and were not affected (P > 0.10) by mineral supplementation. Bulls that received no supplement (CON) had greater (P < 0.01) percentage of sperm with distal midpiece reflex (6.9 vs 4.0% for CON and TM supplement, respectively) and Dag or Dag-like defect (2.6 vs 1.4% for CON and TM supplement, respectively) in their ejaculates. Sperm viability after 30 min of incubation were not affected by trace mineral supplementation, but after 3 h incubation, sperm viability tended to differ (P = 0.06) between treatments and tended to be less for CON bulls (48.5%) compared to ZNCU bulls (55.1%). Among contrast comparisons, trace mineral supplemented bulls had greater (P < 0.05) percentage of viable sperm at 3 h post collection and reactive oxygen resistant sperm than CON bulls. Addition of Zn to trace mineral containing Cu (ZNCU) improved (P < 0.05) percentage of sperm in the ejaculate with high mitochondrial energy potential and viable sperm with intact acrosome membrane. In summary, it appears the homeostasis mechanisms for bull trace mineral maintenance are extremely efficient and mineral supplementation of mature and peripubertal bulls did not have major improvements in any laboratory or chute-side measures of bull fertility, however bulls exposed to breeding or in environments with diet antagonists might respond differently.

Effect of estradiol preceding and progesterone subsequent to ovulation on proportion of postpartum beef cows pregnant

Two experiments were conducted to examine the effect of plasma concentrations of 17β-estradiol (E₂) preceding and progesterone (P₄) subsequent to ovulation on proportions of beef cows pregnant following embryo transfer. Timing of ovulation (d 0) among postpartum cows was synchronized and cows that expressed estrus were removed from each study. In Experiment 1, plasma E₂ concentration on d 0 was used to classify cows (n = 353) into Low, Medium, and High E₂ groups. Pregnancy rate for cows with Low, Medium, or High E₂ concentrations were different (P < 0.05). In Experiment 2, there were multiple administrations of PGF_2α to evaluate the independent effects of Low or High E₂ before ovulation and Low or Normal (no treatment) P₄ after ovulation on proportions of cows pregnant. Treatment groups in Experiment 2, therefore, were: Low E₂-Low P₄ (LL; n = 71), Low E₂-Normal P₄ (LN; n = 69), High E₂-Low P₄ (HL; n = 74), and High E₂-Normal P₄ (HN; n = 73). Concentrations of P₄ on d 7 subsequent to ovulation were less (P < 0.05) in cows of the HL compared to HN, and in LL compared to LN groups. Concentrations of E₂ on d -2, 0, and change in E₂ (d -2 to d 0) had a positive effect (P < 0.008) on pregnancy rates. In summary, relatively greater E₂ concentrations preceding ovulation; and relatively greater P₄ concentrations subsequent to ovulation combined with lesser E₂ concentrations preceding ovulation had a positive effect on proportions of postpartum cows pregnant.

Loci associated with conception rate in crossbred beef heifers

The inability of beef cattle to maintain full term pregnancies has become an economic concern for the beef industry. Herd management and nutritional improvements have alleviated environmental impacts on embryonic and fetal loss, yet additional gains can be made through genomic selection. The objectives of this study were to identify loci and gene-sets in crossbred beef heifers associated with the number of services required to become pregnant (TBRD) and heifer conception rate at first service (HCR1). Heifers (n = 709) from a commercial beef operation underwent one round of artificial insemination, before exposure to bulls for natural service for 50 days. Pregnancy and time of conception was determined by ultrasound 35 days after the breeding season. Heifers were genotyped using the GeneSeek (Lincoln, NE) Bovine GGP50K BeadChip prior to genome-wide association analyses (GWAA) conducted using an EIGENSTRAT-like model to identify loci associated (P < 1 × 10⁻⁵) with TBRD and HCR1. One locus was associated (P = 8.97 × 10⁻⁶) with TBRD on BTA19 and included the positional candidate gene ASIC2, which is differentially expressed in the endometrium of fertility classified heifers, and the positional candidate gene, SPACA3. Gene-set enrichment analyses using SNP (GSEA-SNP) data, was performed and identified one gene-set, oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen as enriched (NES = 3.15) with TBRD and contained nine leading edge genes that contributed to the enrichment of the gene set. The enriched gene-set is involved in catalyzing oxidation-reduction reactions, which have been associated with oxidative stressors impacting pregnancy success. No loci were associated nor gene-sets enriched with HCR1. Identification of loci, positional candidate genes, gene-sets and leading edge genes enriched for fertility facilitate genomic selection that allows producers to select for reproductively superior cattle, reduce costs associated with infertility, and increase percent calf crop.

Pregnancy associated glycoproteins (PAGs) and pregnancy loss in high vs sub fertility heifers

Reproductive inefficiency and infertility are major financial burdens to domestic livestock. Variables associated with these reproductive losses during early gestation include contributions from the oocyte, uterus, sperm, embryo and placenta. Bovine pregnancy associated glycoproteins (PAG) are produced by the binucleate cells of the ruminant placenta and can be used to diagnose pregnancy. Increased circulating concentrations of PAG early in gestation have been correlated with pregnancy success and decreased concentrations are predictive of impending embryonic mortality in both beef and dairy cattle. The objectives of the current study were to determine whether: 1) heifer fertility status is associated with circulating concentrations of PAG and pregnancy loss; and 2) PAG concentrations within the same animal are repeatable across multiple pregnancies. We hypothesized maternal PAG concentrations would be increased in high fertility compared to subfertile heifers but not repeatable across subsequent pregnancies in the same heifer. Serial embryo transfer (ET; n = 4 rounds) was used to classify predominately Angus heifers (n = 92) as highly fertile (HF = 30; 100% pregnancy success) or subfertile (SF = 62; average = 33%; range = 25-75% pregnancy success) based on day 28 ultrasound diagnosis. Blood samples were collected at both day 28 and 44 for quantification of circulating PAG concentrations by an in house PAG ELISA with antibodies raised against early secreted PAGs. Pregnancy was terminated at day 44 of gestation and heifers were allowed 30 days recovery before synchronization for the next ET. Only heifers that were diagnosed pregnant by ultrasound were used in this study (HF: n = 30, SF: n = 62). Serum concentrations of PAGs were not different between HF (5.90 ± 0.27 ng/mL) and SF (5.56 ± 0.31 ng/mL; P = 0.16) heifers at day 28 of gestation nor was there a difference at day 44 of gestation (P = 0.32). Subfertile heifers had increased pregnancy loss between days 28 and 44 of gestation. Based on odds ratio analysis, SF heifers had a 2.41 times chance to undergo pregnancy loss between day 28-44 compared to HF heifers (P < 0.05). There was no correlation (P > 0.05) in maternal circulating concentrations of PAG between pregnancies on day 28 or 44 of gestation in samples obtained from HF heifers. In summary, circulating concentrations of PAG are not different between HF and SF heifers; however, HF classified heifers have decreased pregnancy loss between days 28 and 44 of gestation.

Genomic prediction of continuous and binary fertility traits of females in a composite beef cattle breed

Reproduction efficiency is a major factor in the profitability of the beef cattle industry. Genomic selection (GS) is a promising tool that may improve the predictive accuracy and genetic gain of fertility traits. There is a wide range of traits used to measure fertility in dairy and beef cattle including continuous (days open), discrete (pregnancy status), and count (number of inseminations) responses. In this study, a joint analysis of age of puberty (AOP), age at first calving (AOC), and the heifer pregnancy status (HPS) was performed. Data used in this study consisted of records from 1,365 Composite Gene Combination (CGC; 50% Red Angus, 25% Charolais, 25% Tarentaise) first parity females born between 2002 and 2011. The pedigree file included 5,374 animals. A total of 3,902 animals were genotyped with different density SNP chips (3K to 50K SNP). Animals genotyped with low-density arrays were imputed to higher density (BovineSNP50 BeadChip) using FImpute. Data were analyzed using univariate and multivariate classical quantitative models (pedigree based) and univariate genomic approaches. For the latter, 3 different Bayesian methods (BayesA, BayesB, and BayesCπ) were implemented and compared. Estimates of heritabilities using univariate and multivariate analyses based on pedigree relationships ranged between 0.03 (for AOC) to 0.2 (AOP). Heritability of pregnancy status was 0.15 and 0.09 using the univariate and multivariate analyses, respectively. Genetic correlation between pregnancy status and the other 2 traits was low being 0.08 with age at puberty and -0.10 with age at first calving. Heritability estimates were slightly higher using genomic rather than average additive relationships. The accuracy of genomic prediction was similar across the 3 Bayesian methods with higher accuracies for age of puberty than the age at first calving likely due to the higher heritability of the former. The prediction of the binary pregnancy status measured using the area under the curve increased by 27% to 29% compared to a random classifier. Due to the small size of the data, all estimates have large posterior standard deviations and results should be interpreted with caution.

Developmental and reproductive characteristics of beef heifers classified by pubertal status at time of first breeding

Data collected for 10 or more years at the West Central Research and Extension Center, North Platte, NE ( = 1,104); the Gudmundsen Sandhills Laboratory, Whitman, NE ( = 1,333); and the USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT ( = 1,176) were retrospectively analyzed to evaluate growth and reproductive performance of beef heifers classified by pubertal status before first breeding. Concentrations of progesterone in serum from 2 blood samples collected 9 to 11 d apart before the breeding season classified heifers as pubertal (progesterone ≥ 1.0 ng/mL in 1 or both samples) or nonpubertal (progesterone < 1.0 ng/mL in both samples). Average date of birth was earlier ( < 0.06) and proportion born in the first 21 d of the calving season was 10 to 20 percentage points greater for heifers that were pubertal at the start of breeding compared with heifers not pubertal by the start of breeding. Heifers that were pubertal by the start of breeding were 7 to 10 kg heavier ( < 0.01) and 1 cm taller ( < 0.01) at weaning than heifers not pubertal by the start of breeding. Differences in BW persisted through the start of breeding to pregnancy diagnosis. Heifers that achieved puberty by the start of breeding had greater ( < 0.05) feed intake and G:F during postweaning development and had greater ( < 0.01) LM area and fat thickness over the LM at approximately 1 yr of age compared with heifers not pubertal by the start of breeding. Heifers that achieved puberty before the start of breeding had greater ( < 0.01) ADG from birth to weaning but slower ( < 0.10) rates of gain from the start of breeding through pregnancy diagnosis. Pregnancy rate was greater ( < 0.01) for heifers that were pubertal at the start of breeding. In heifers that became pregnant, those that were pubertal before the start of breeding calved earlier ( < 0.01), with a greater ( < 0.01) percentage calving in the first 21 d of calving than heifers not pubertal at the start of breeding. Calves from heifers that achieved puberty before the start of breeding were heavier at weaning ( < 0.01) than calves from heifers that had not achieved puberty by the start of breeding. In summary, heifers that failed to achieve puberty by the start of breeding were less desirable for several traits evaluated. Based on these results, implementing feeding strategies to increase the proportion of heifers that achieve puberty before first breeding could result in propagation of undesirable characteristics.

Glycosylation and immunocytochemistry of binucleate cells in pronghorn (Antilocapra americana, Antilocapridae) show features of both Giraffidae and Bovidae

Although the pronghorn (Antilocapra americana) resembles an antelope, its nearest relatives are the giraffe and okapi. In this study we have examined the placentae of 6 pronghorns using lectin- and immunocytochemistry to identify giraffid and bovid features. Binucleate cells (BNC) of the placenta exhibited features intermediate between those of the giraffe and bovine; Dolichos biflorus agglutinin binding - strong in the bovine BNC and absent in the giraffe - was evident in only a subpopulation of BNC while binding to blood vessels, as in the giraffe. Binding of Phytolacca americana agglutinin resembled that of the giraffe and okapi whereas many other glycans were found in all four clades. PAG antigens were similar to bovine and okapi but not giraffe. In summary, although the pronghorn outwardly resembles an antelope, placental BNC show giraffid features. Although each clade has its own individual characteristics, there are far more similarities than differences between them, emphasizing the common ancestry of all four clades.

147 EFFECT OF OVULATORY FOLLICLE DIAMETER ON THE OOCYTE TRANSCRIPTOME IN BEEF COWS

Inadequate oocyte competence is a potential explanation for reduced pregnancy rates and(or) embryonic/fetal mortality when small dominant follicles are induced to ovulate prematurely with gonadotropin releasing hormone (GnRH). Our hypothesis was that the physiological status of an ovulatory follicle has a direct effect on competence of the oocyte and resulting embryo. The objective was to determine if the transcriptome of oocytes differ depending on whether they are collected from small or large dominant follicles following a GnRH-induced gonadotropin surge. Suckled beef cows (n = 350) were pre-synchronized with a 5-day CIDR protocol. Following pre-synchronization, GnRH1 was administered on Day –9, prostaglandin F on Day –2, GnRH2 (to initiate the ovulatory process) on Day 0, and dominant follicles were transvaginally aspirated on Day 1 before follicular rupture. On Day 0, cows were divided into small (<11.7 mm; no oestrus expression), or large (>12.5 mm; no oestrus expression) groups based on dominant follicle diameter. Oocytes were individually collected after aspiration, and RNA was later extracted from pools of 4 oocytes (n = 6 oocyte pools from both small and large follicles) and sequenced on an Illumina HiSEqn 2000 (single reads, 100 bases; Illumina Inc., San Diego, CA, USA). The sequences were tiled against a ~23 500 member bovine transcript reference obtained from the National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov/). Tiling to target transcripts required a minimum match of 50 bases with at least 96% identity. Tiling counts were displayed as reads per kilobase of transcript per million mapped reads (RPKM) values, which were obtained by correcting for the length of each target (in kb) and the number of total tiled reads (in millions). Differences between groups were defined by two-tailed t-test and gene lists were selected based on P-values <0.02. Numerous differences in transcript abundance were characterised between oocytes from small and large dominant follicles. Follistatin-like 5 expression was increased (P < 0.02) in oocytes collected from large dominant follicles compared with oocytes collected from small dominant follicles. Several genes were associated with the ubiquitin pathway (e.g. ubiquitin conjugating enzyme, ubiquitin like protein-7) and were up-regulated (P < 0.02) in oocytes from large versus small dominant follicles. In addition, 4 members of the zinc finger protein family were up-regulated (P < 0.02) and 4 members were down-regulated (P < 0.02) in oocytes from large compared with small dominant follicles. In summary, some of the genes that were highly differentially regulated in bovine oocytes between small and large dominant follicles included members of the zinc finger and ubiquitin pathways, which may reflect differences in transcriptional regulation and protein turnover, respectively, between oocytes collected from large and small follicles. Study was supported by AFRI Grant no. 2013–67015–21076 from the USDA National Institute of Food and Agriculture (Washington, DC).

Predicting Embryo Presence and Viability

Pregnancy establishment, followed by birth of live offspring, is essential to all mammals. The biological processes leading up to pregnancy establishment, maintenance, and birth are complex and dependent on the coordinated timing of a series of events at the molecular, cellular, and physiological level. The ability to ovulate a competent oocyte, which is capable of undergoing fertilization, is only the initial step in achieving a successful pregnancy. Once fertilization has occurred and early embryonic development is initiated, early pregnancy detection is critical to provide proper prenatal care (humans) or appropriate management (domestic livestock). However, the simple presence of an embryo, early in gestation, does not guarantee the birth of a live offspring. Pregnancy loss (embryonic mortality, spontaneous abortions, etc.) has been well documented in all mammals, especially in humans and domestic livestock species, and is a major cause of reproductive loss. It has been estimated that only about 25-30% of all fertilized oocytes in humans result in birth of a live offspring; however, identifying the embryos that will not survive to parturition has not been an easy task. Therefore, investigators have focused the identification of products in maternal circulation that permit the detection of an embryo and assessment of its well-being. This review will focus on the advances in predicting embryonic presence and viability, in vivo.

Triennial Reproduction Symposium: deficiencies in the uterine environment and failure to support embryonic development

Pregnancy failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. The focus of this review is on cattle and factors affecting and mechanisms related to uterine insufficiency for pregnancy. A variety of factors contribute to embryonic loss and it may be exacerbated in certain animals, such as high-producing lactating dairy cows, and in some cattle in which estrous synchronization and timed AI was performed, due to reduced concentrations of reproductive steroids. Recent research in beef cattle induced to ovulate immature follicles and in lactating dairy cows indicates that deficient uterine function is a major factor responsible for infertility in these animals. Failure to provide adequate concentrations of estradiol before ovulation results in prolonged effects on expression and localization of uterine genes and proteins that participate in regulating uterine functions during early gestation. Furthermore, progesterone concentrations during early gestation affect embryonic growth, interferon-tau production, and uterine function. Therefore, an inadequate uterine environment induced by insufficient steroid concentrations before and after ovulation could cause early embryonic death either by failing to provide an adequate uterine environment for recognition of embryo signaling, adhesion, and implantation or by failing to support appropriate embryonic growth, which could lead to decreased conceptus size and failed maternal recognition of pregnancy.

Circulating bovine pregnancy associated glycoproteins are associated with late embryonic/fetal survival but not ovulatory follicle size in suckled beef cows

The objective was to examine the relationship between ovulatory follicle size and embryo and fetal survival by using circulating concentrations of bovine pregnancy associated glycoproteins (bPAG) to detect the presence of an embryo or fetus and monitor placental function. Before examining the relationship between bPAG, ovulatory follicle size, and embryo and fetal survival, the half-life of bPAG was determined in Exp. 1. The half-life of bPAG after PGF2α-induced abortion on d 32 to 36 postinsemination was 35.8 ± 21.9 h (mean ± SD; range 7.1 to 78.5 h). In Exp. 2, suckled beef cows (n = 91) were treated with the CO-Synch protocol (GnRH on d -9, PGF2α on d -2, and GnRH and AI 48 h later [d 0]) and classified into 1 of 2 ovulatory follicle size groups: 1) small follicle (<12.5 mm; n = 25) or 2) large follicle (≥ 12.5 mm; n = 66). The first increase (P < 0.0001) in serum bPAG occurred in pregnant cows on d 24 after insemination and circulating bPAG decreased before a decrease in progesterone in 3 of 4 cows that lost an embryo or fetus. Pattern of secretion of bPAG in serum from d 24 to 60 after insemination (d 0) was affected by day (P < 0.0001), but not ovulatory follicle size. In Exp. 3, suckled beef cows (n = 1164) were administered the CO-Synch protocol either with (donor cows; n = 810) or without (recipient cows; n = 354) AI on d 0. Single embryos (n = 394) or oocytes (n = 45) were recovered from the donor cows [d 7; embryo transfer (ET)] and all live embryos were transferred into recipients the same day. Cows were classified on d 0 as having a small (<12.5 mm) or large (≥ 12.5 mm) ovulatory follicle, and randomly chosen as donors or recipients to remove confounding effects of ovulatory follicle size on fertility. Serum concentration of bPAG at d 28 was not affected by ovulatory follicle size (P = 0.85), embryo stage at ET (P = 0.75), embryo quality at ET (P = 0.64), estradiol at GnRH2 (P = 0.62) or serum progesterone at ET (d7; P = 0.14). Compared with cows that maintained pregnancy (n = 176), cows that exhibited late embryonic or fetal mortality (n = 19) after d 28 had decreased (P < 0.05) concentrations of bPAG on d 28. In summary, there was no relationship between serum bPAG and ovulatory follicle size or embryo stage or quality at ET; however, cows that lost an embryo after d 28 had reduced concentrations of bPAG on d 28 compared with cows that maintained pregnancy.

Does β-hydroxybutyrate concentration influence conception date in young postpartum range beef cows?

Cows in negative energy balance after calving often have reduced reproductive performance, which is mediated by metabolic signals. The objective of these studies was to determine the association of serum metabolites, days to first postpartum ovulation, milk production, cow BW change, BCS, and calf performance with conception date in spring-calving 2- and 3-yr-old beef cows grazing native range. In Exp. 1, cows were classified by conception date in a 60-d breeding season as early (EARLY; conceived in first 15 d of breeding) or late conception (LATE; conceived during the last 45 d of breeding). Beginning on d 35 postpartum, blood samples were collected twice per week for serum metabolite analysis and progesterone analysis to estimate days to resumption of estrous cycles. As a chute-side measure of nutrient status and glucose sufficiency, whole-blood β-hydroxybutyrate (BHB) concentrations were measured 14 ± 2 d before breeding. In Exp. 2, cows were classified by subsequent calving date resulting from a 55 ± 2 d breeding season as conceiving either early (EARLY; conceived in first 15 d of breeding) or late (LATE; conceived during the remaining breeding season). Blood samples were collected in 2 periods, 30 ± 4 d before calving and 14 ± 3 d before the initiation of breeding, to determine circulating concentrations of IGF-I and BHB. In Exp. 1, BHB and serum glucose concentrations were less (P ≤ 0.04) in EARLY cows than LATE cows. Serum insulin concentrations were greater (P = 0.03) in EARLY cows relative to LATE cows. Milk production and composition did not differ (P ≥ 0.24) by conception date groups. In Exp. 2, cow age × sample period × conception date interaction (P < 0.01) occurred for serum BHB concentrations. Serum BHB concentrations were similar (P > 0.10) for 2-yr-old cows (in greater nutritional plane compared with Exp. 1) regardless of their conception date classification and sampling period. However, precalving serum BHB concentrations were greater (P < 0.01) for LATE than EARLY in 3-yr-old cows with no difference (P = 0.86) at prebreeding. Serum IGF-1 concentrations were greater (P < 0.01) for EARLY cows relative to LATE cows at precalving and prebreeding. This study indicates that blood BHB concentrations during times of metabolic dysfunctions may provide a more sensitive indicator of energy status than body condition, predicting rebreeding competence in young beef cows as measured by interval from calving to conception.

Pregnancy establishment and maintenance in cattle

A single ovulation, reciprocal embryo transfer study was used to investigate effects of oocyte competence and maternal environment on pregnancy establishment and maintenance in beef cows. Estrous cycles were synchronized in suckled beef cows and embryo donors were inseminated on d 0 (n = 810). Cows were classified on d 0 as having a small (<12.5 mm) or large (≥12.5 mm) ovulatory follicle and randomly chosen as donors or recipients to remove confounding effects of ovulatory follicle size on fertility. Embryos (n = 393) or oocytes (n = 44) were recovered on d 7, and all viable embryos were transferred into recipients (n = 354). All statistical analyses were conducted using the GLM procedure of SAS. Path analysis (with significance set at P < 0.10) was used to examine potential cause-effect relationships among the measured variables. Greater donor cow BW, circulating estradiol concentration at insemination, postpartum interval, and ovulatory follicle size directly increased (P < 0.10) fertilization success. Greater donor cow age was the only factor that directly decreased (P < 0.10) fertilization success. Viability of d-7 embryos was directly inhibited (P < 0.10) by rapid follicular growth rate from d -2 to 0 and heavier BW. Direct beneficial effects to embryo viability were increased serum progesterone concentration on d -2 and ovulatory follicle size. Pregnancy maintenance from d 7 to 27 was enhanced (P < 0.10) by increased serum estradiol concentration on d 0 and progesterone concentration on d 7 in the recipient cow. Increased follicular diameter in the recipient cow on d 0 was detrimental to pregnancy maintenance from d 7 to 27. This manuscript defines the complex interplay and relative contributions of endocrine and physical factors both prior and subsequent to fertilization that influence both oocyte competence and maternal environment and their roles in establishment and maintenance of pregnancy.

Reproductive performance of heifers offered ad libitum or restricted access to feed for a one hundred forty-day period after weaning

Reproductive performance was evaluated in composite heifers born over a 3-yr period that were randomly assigned to control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding for a 140-d period, beginning about 2 mo after weaning at 6 mo of age and ending at about 12.5 mo of age. Heifers were fed a diet of 67% corn silage, 18% alfalfa, and 9% of a protein-mineral supplement (DM basis). Restricted heifers consumed 27% less feed over the 140 d and had less ADG (0.53 +/- 0.01 vs. 0.65 +/- 0.01 kg/d; P < 0.001) than control heifers. After 140 d, all heifers were placed in common pens and subjected to an estrous synchronization protocol to facilitate AI at about 14 mo of age. Heifers were then exposed to bulls for the remainder of a 51-d breeding season. Average BW of heifers diverged within 28-d after initiation of feed restriction, and differences (P < 0.001) persisted through the prebreeding period (309 +/- 1 vs. 326 +/- 1 kg at approximately 13.5 mo of age) and subsequent grazing season (410 +/- 2 vs. 418 +/- 2 kg at about 19.5 mo of age). From the end of the 140-d restriction at about 12.5 to 19.5 mo of age, ADG was greater (P < 0.001) in restricted heifers than control heifers (0.51 +/- 0.01 vs. 0.47 +/- 0.01 kg/d). Proportion of heifers attaining puberty by 14 mo of age tended to be less (P = 0.1) in restricted (60 +/- 3%) than control-fed heifers (68 +/- 3%). Mean BW at puberty was less (P < 0.01) in restricted (309 kg) than control (327 kg) heifers. Pregnancy rate from AI tended to be less (P = 0.08) in restricted (48 +/- 4%) than control heifers (57 +/- 3%). Proportion of animals that were pubertal at breeding and pregnant from AI were positively associated (P < 0.1) with heifer age and ADG from birth to beginning of study. Final pregnancy rates were 87 and 91% for restricted and control heifers, respectively (P = 0.27). Day of breeding season that conception occurred was negatively associated with ADG from birth to weaning (P = 0.005), but was not associated with ADG within treatment (P = 0.60). Economic analysis revealed a $33 reduction in cost to produce a pregnant heifer under the restricted protocol when accounting for pregnancy rates and differences in BW and market prices between selection at weaning and marketing as open heifers at l.5 yr of age. A potential economic advantage exists for rearing replacement heifers on a restricted level of feeding during the postweaning period.

Synchronization of estrus in suckled beef cows for detected estrus and artificial insemination and timed artificial insemination using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone

We determined whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or estrous detection plus TAI, and whether adding a controlled internal device release (CIDR) to GnRH-based protocols would enhance fertility. Estrus was synchronized in 2,598 suckled beef cows at 14 locations, and AI was preceded by 1 of 5 treatments: 1) a CIDR for 7 d with 25 mg of PG F(2alpha) (PGF) at CIDR removal, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received 100 mug of GnRH and TAI at 84 h (control; n = 506); 2) GnRH administration, followed in 7 d with PGF, followed in 60 h by a second injection of GnRH and TAI (CO-Synch; n = 548); 3) CO-Synch plus a CIDR during the 7 d between the first injection of GnRH and PGF (CO-Synch + CIDR; n = 539); 4) GnRH administration, followed in 7 d with PGF, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received GnRH and TAI at 84 h (Select Synch & TAI; n = 507); and 5) Select Synch & TAI plus a CIDR during the 7 d between the first injection of GnRH and PGF (Select Synch + CIDR & TAI; n = 498). Blood samples were collected (d -17 and -7, relative to PGF) to determine estrous cycle status. For the control, Select Synch & TAI, and Select Synch + CIDR & TAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed using the AM/PM rule. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of cows cycling at the initiation of treatments was 66%. Pregnancy rates (proportion of cows pregnant to AI of all cows synchronized during the synchronization period) among locations across treatments ranged from 37% to 67%. Pregnancy rates were greater (P < 0.05) for the Select Synch + CIDR & TAI (58%), CO-Synch + CIDR (54%), Select Synch & TAI (53%), or control (53%) treatments than the CO-Synch (44%) treatment. Among the 3 protocols in which estrus was detected, conception rates (proportion of cows that became pregnant to AI of those exhibiting estrus during the synchronization period) were greater (P < 0.05) for Select Synch & TAI (70%; 217 of 309) and Select Synch + CIDR & TAI (67%; 230 of 345) cows than for control cows (61%; 197 of 325). We conclude that the CO-Synch + CIDR protocol yielded similar pregnancy rates to estrous detection protocols and is a reliable TAI protocol that eliminates detection of estrus when inseminating beef cows.

Genetic parameter estimates for scrotal circumference and semen characteristics of Line 1 Hereford bulls

The objectives of this study were to estimate heritability for scrotal circumference (SC) and semen traits and their genetic correlations (rg) with birth weight (BRW). Semen traits were recorded for Line 1 Hereford bulls (n = 841), born in 1963 or from 1967 to 2000, that were selected for use at Fort Keogh (Miles City, MT) or for sale. Semen was collected by electroejaculation when bulls were a mean age of 446 d. Phenotypes were BRW, SC, ejaculate volume, subjective scores for ejaculate color, swirl, sperm concentration and motility, and percentages of sperm classified as normal and live or having abnormal heads, abnormal midpieces, proximal cytoplasmic droplets (primary abnormalities), bent tails, coiled tails, or distal cytoplasmic droplets (secondary abnormalities). Percentages of primary and secondary also were calculated. Data were analyzed using multiple-trait derivative-free REML. Models included fixed effects for contemporary group, age of dam, age of bull, inbreeding of the bull and his dam, and random animal and residual effects. Random maternal and permanent maternal environmental effects were also included in the model for BRW. Estimates of heritability for BRW, SC, semen color, volume, concentration, swirl, motility, and percentages of normal, live, abnormal heads, abnormal midpieces, proximal cytoplasmic droplets, bent tails, coiled tails, distal cytoplasmic droplets, and primary and secondary abnormalities were 0.34, 0.57, 0.15, 0.09, 0.16, 0.21, 0.22, 0.35, 0.22, 0.00 0.16, 0.37, 0.00 0.34 0.00, 0.30, and 0.33, respectively. Estimates of rg for SC with color, volume, concentration, swirl, motility, and percentages of live, normal, and primary and secondary abnormalities were 0.73, 0.20, 0.77, 0.40, 0.34, 0.63, 0.33, -0.36, and -0.45, respectively. Estimates of rg for BRW with SC, color, volume, concentration, swirl, motility, and percentages live, normal, and primary and secondary abnormalities were 0.28, 0.60, 0.08, 0.58, 0.44, 0.21, 0.34, 0.20, -0.02, and -0.16, respectively. If selection pressure was applied to increase SC, all of the phenotypes evaluated would be expected to improve. Predicted correlated responses in semen characteristics per genetic SD of selection applied to SC were 0.87 genetic SD or less. If selection pressure was applied to reduce BRW, the correlated responses would generally be smaller but antagonistic to improving all of the phenotypes evaluated. Predicted correlated responses in SC and semen characteristics per genetic SD of selection applied to BRW were less than 0.35 genetic SD.

Milk yield of primiparous beef cows from three calving systems and varied weaning ages

Primiparous beef cows produced in 3 calving systems were used in a 2-yr study with a completely random design to measure milk yield throughout a 190-d lactation (2002, n = 20; 2003, n = 24 per calving system). Calving occurred in late winter (average calving date = February 4 +/- 2 d), early spring (average calving date = March 30 +/- 2 d), and late spring (average calving date = May 26 +/- 1 d). Additionally, cows used in this study had been weaned at varied ages as calves, creating 6 dam treatments. Dam age at weaning was 140 (late spring), 190 (late winter, early spring, late spring), or 240 (late winter, early spring) d of age. Milk production was measured by using the weigh-suckle-weigh technique at an average of 20, 38, 55, 88, 125, 163, and 190 d in milk. Milk yield for the 190-d lactation period was calculated as area under the curve by trapezoidal summation. Data were analyzed with a model containing treatment, year, and their interaction. Orthogonal contrasts were used to separate effects when treatment was significant (P < 0.10). Total milk yield did not differ (P = 0.42) between cows in the late winter and early spring systems, but cows in the late spring system tended to differ (P = 0.09) from the average of the other 2 systems. Cows in the late spring calving system had increased milk yield in 2002 and lesser milk yield in 2003 compared with the other calving systems (treatment x year interaction, P < 0.001). Cows born in late spring that had been weaned at 140 d of age produced more (P = 0.05) total milk than those weaned at 190 d of age. Peak milk yield was affected (P < 0.001) by treatment and showed a treatment x year interaction (P = 0.006). Day of peak lactation differed among treatments (P = 0.002), with cows in the late winter system peaking later (P = 0.007) than early spring cows, and late spring cows peaking earlier (P = 0.004) than the average of late winter and early spring cows. The average date of peak lactation was May 4 for the late winter system, May 31 for the early spring system, and July 19 for the late spring system. Calf ADG differed (P < 0.001) for the late spring system compared with the average of the late winter and early spring systems, but the relationship interacted with year (P < 0.001). Cow BW and BW change differed among treatments (P < 0.004), with much of the difference associated with the amount of milk produced or the timing of peak lactation. Season of calving affects milk yield of primiparous cows grazing Northern Great Plains rangelands and ADG of their calves.

Quantitative trait loci with additive effects on palatability and fatty acid composition of meat in a Wagyu-Limousin F2 population

A whole-genome scan was conducted on 328 F(2) progeny in a Wagyu x Limousin cross to identify quantitative trait loci (QTL) affecting palatability and fatty acid composition of beef at an age-constant endpoint. We have identified seven QTL on five chromosomes involved in lipid metabolism and tenderness. None of the genes encoding major enzymes involved in fatty acid metabolism, such as fatty acid synthase (FASN), acetyl-CoA carboxylase alpha (ACACA), solute carrier family 2 (facilitated glucose transporter) member 4 (SLC2A4), stearoyl-CoA desaturase (SCD) and genes encoding the subunits of fatty acid elongase, was located in these QTL regions. The present study may lead to a better-tasting and healthier product for consumers through improved selection for palatability and lipid content of beef.

Effect of early gestational undernutrition on angiogenic factor expression and vascularity in the bovine placentome

The effect of early gestation maternal undernutrition followed by realimentation on placentomal vascular growth and angiogenic factor expression was determined in multiparous beef cows bred to the same bull. Cows gestating only female fetuses (n = 30) were fed in equal numbers to meet the NRC requirements (control) or were fed below the NRC requirements to lose BW (nutrient restricted; NR) from d 30 to 125 of gestation. After slaughter on d 125 of gestation, 10 control and 10 NR cows were necropsied. The remaining NR cows (n = 5) were then fed to achieve a BCS equal to their control group contemporaries (n = 5) by d 220 of gestation. All cows were fed the control diet from d 220 until 250 of gestation, when the remaining control and NR cows were slaughtered and necropsied. At necropsy, placentomes were fixed via perfusion of the caruncular and cotyledonary arteries to determine capillary vascular density. Cotyledonary (fetal placental) and caruncular (maternal placental) tissues also were snap-frozen in liquid nitrogen, and mRNA concentrations of vascular endothelial growth factor and its 2 specific receptors, fms-like tyrosine kinase and kinase insert domain containing receptor, as well as placental growth factor, were determined. There was no effect of diet or day of gestation on the percentage of proliferating caruncular cells. Although diet did not impact cotyledonary cellular proliferation, there was an increase (P < 0.05) in the percentage of proliferating cells on d 250 compared with d 125 of gestation. Nutrient restriction from d 30 to 125 increased (P < or = 0.10) placental mRNA concentrations of placental growth factor and fms-like tyrosine kinase; however, there was no alteration in vascularity. By d 250 of gestation, NR cows had increased (P < 0.05) caruncular capillary surface density and decreased (P < 0.05) cotyledonary capillary area density, capillary number density, and capillary surface density compared with control cows. Although nutrient restriction had little effect on placental vascularity by d 125, upon realimentation, alterations in vascularity became apparent by d 250 of gestation, suggesting a placental programming effect.

Effects of restricted feeding of beef heifers during the postweaning period on growth, efficiency, and ultrasound carcass characteristics1

Traits used for identification of replacement beef heifers and feeding levels provided during postweaning development may have major financial implications due to effects on maintenance requirements and level of lifetime production. The current study evaluated the effects of 2 levels of feeding during the postweaning period on growth, G:F, and ultrasound carcass measurements of heifers, and the associations among these traits. Heifers (1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise) born in 3 yr were randomly assigned to a control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding during a 140-d postweaning period. Heifers were individually fed a diet of 68% corn silage, 18% alfalfa, and protein-mineral supplement (DM basis) in pens equipped with Calan gates. Ultrasound measurements of LM area, intramuscular fat, and subcutaneous fat thickness over the LM were made on d 140 (382 +/- 0.8 d of age). Average daily DMI was 4.1 and 5.6 kg/d for restricted and control heifers, respectively (P < 0.001). Feed restriction decreased (P < 0.001) BW (292 vs. 314 kg), ADG (0.52 vs. 0.65 kg/d), LM area (55 vs. 59 cm2), intramuscular fat (3.2 vs. 3.5%), and subcutaneous fat thickness over the LM (3.2 vs. 3.9 mm), but increased G:F (0.12 vs. 0.11) when compared with control at the end of the 140-d study. The magnitude of the associations of DMI with ADG (r = 0.32 vs. 0.21), 140-d BW (r = 0.78 vs. 0.36), hip height (r = 0.57 vs. 0.17), LMA (r = 0.30 vs. 0.18), and BCS (r = 0.17 vs. 0.11) was greater in restricted- than control-fed heifers. Variance of residual feed intake, calculated within each treatment, was greater (P < 0.01) in control (0.088) than restricted (0.004) heifers, and magnitude of association between residual feed intake and average DMI was greater in control (r = 0.88) than restricted (r = 0.41) heifers. Pregnancy rate tended (P = 0.11) to be reduced in heifers that had been developed on restricted feeding (86.3 +/- 2.3 vs. 91.5 +/- 2.3%). However, ADG was greater (P < 0.001) in restricted than control heifers (0.51 vs. 0.46 kg/d) while grazing native range in the 7 mo after restriction. In summary, restricted heifers consumed 22% less feed on a per-pregnant-heifer basis during the development period and had a greater magnitude of association between DMI and several growth-related traits at the end of the 140-d postweaning feeding period, which is indicative of improved efficiency.

Influence of seasonal forage quality on glucose kinetics of young beef cows1

Extensive range livestock production systems in the western United States rely heavily on rangeland forages to meet the nutritional needs of grazing livestock throughout the year. Interannual variation in the quantity and quality of rangeland forage in the Northern Great Plains, as well as throughout much of the western United States, may play a pivotal role in how well grazing ruminants sequester nutrients in their tissues. This variation in forage quality may influence the ability of a beef cow to utilize dietary nutrients via changes in tissue responsiveness to insulin. Identifying specific periods and production states in which this phenomenon is manifested will provide insight into the development and implementation of strategic and targeted supplementation practices that improve nutrient utilization during times of nutritional imbalance and may improve the lifetime productivity of grazing range beef cows. A 2-yr study was conducted to monitor serum metabolites, glucose kinetics during glucose tolerance tests, and forage chemical composition every 90 d in young cows (2 to 4 yr of age; n = 28). In yr 1 and 2, cows were managed on 4 pastures varying in size from 36 to 76 ha in yr 1 and 49 to 78 ha in yr 2. Regardless of year, cow age, or cow physiological status, the main factor influencing glucose half-life was season of the year (P = 0.02). Effects of season on glucose half-life closely followed assessments describing forage quality, with glucose half-lives of 46, 39, 43, and 51 +/- 3.9 min for May, August, December, and March, respectively. Elevated glucose half-life during seasons in which forage quality is of lower nutritive value indicated that tissue responsiveness to the actions of insulin followed seasonal changes in forage quality. Glucose half-life tended (P = 0.09) to decrease between May and August, increased (P = 0.04) between December and March, and showed a tendency (P = 0.10) to decrease in seasons of greater nutrient density (May and August) compared with seasons of lower nutrient density (December and March). Seasonal changes in serum metabolites were also observed and corresponded with changes in forage quality. The results support our hypothesis that as the season progresses and forage quality declines, maternal tissues become less responsive to insulin, indicating that targeted supplementation with glucogenic precursors during these seasons of nutritional stress may improve cow performance.

Quantitative trait loci with additive effects on growth and carcass traits in a Wagyu-Limousin F2 population

A whole-genome scan for carcass traits [average daily gain during the pre-weaning, growth and finishing periods; birth weight; hot carcass weight and longissimus muscle area (LMA)] was performed on 328 F(2) progeny produced from Wagyu x Limousin-cross parents derived from eight founder Wagyu bulls. Nine significant (P </= 0.05) and four suggestive (P </= 0.1) QTL affecting seven growth and carcass traits were identified. Significant QTL were located on bovine chromosomes 2, 4, 7, 9, 12, 16, 17 and 29. A QTL previously reported on chromosome 2 for LMA was also detected in this study. These results provide insight into genetic differences between the Wagyu and Limousin breeds.

Effects of flunixin meglumine and transportation on establishment of pregnancy in beef cows1

Objectives of these studies were to determine the effects of flunixin meglumine (FM) administration on early embryonic mortality and circulating PG and cortisol concentrations in transported and non-transported cows. Cows (n = 483) from 3 locations were used to evaluate the effects of transportation and FM approximately 14 d after AI on the establishment of pregnancy and serum concentrations of progesterone, PGF metabolite (PGFM), and cortisol. Treatments were transport (n = 129), transport + FM (n = 128), no transport (n = 130), and no transport + FM (n = 96). Multiparous cows (n = 224) were used at 2 locations, and nulliparous cows (n = 259) were used at 1 location. The no transport + FM treatment was used at only 2 locations. Flunixin meglumine (approximately 1.1 mg/kg of BW; i.m.) was administered before the cows were separated into transportation groups. Transportation included 4 to 6 h of transportation, without calves, via semitractor trailer. Nontransported cows remained penned, with their calves in adjacent pens, during the same period as the transported cows. Blood samples were collected from all cows before and after treatment and, at 2 locations, approximately 3 h after the onset of treatment. Location affected AI pregnancy rate (P < 0.01). Treatment effects, although not significant (P = 0.16), were of a magnitude to be considered practically important. Cows that received transportation + FM tended (P = 0.07) to have greater AI pregnancy rates (74%) than those that did not receive FM (66%), irrespective of transportation. Cortisol concentration was greater (P < 0.05) for transported cows than for nontransported cows. Cows receiving FM had greater (P < 0.05) AI pregnancy rates than non-FM cows (71 vs. 61%, respectively). Cows receiving transportation had lower (P < 0.01) mean PGFM concentrations than nontransported cows (45.4 vs. 54.6 pg/mL, respectively), and cows receiving FM had lower (P < 0.01) mean PGFM concentrations than non-FM cows (39.4 vs. 60.6, respectively). We conclude that transportation of cows approximately 14 d after AI increased serum cortisol concentrations but did not affect AI pregnancy rates. However, treatment of cows with FM increased AI pregnancy rates, irrespective of whether they were transported.

Beef heifer development within three calving systems

A 3-yr study was conducted to evaluate the effects of calving system, weaning age, and postweaning management on growth and reproduction in beef heifers. Heifer calves (n = 676) born in late winter (average birth date = February 7 +/- 9 d) or early spring (average birth date April 3 +/- 10 d) were weaned at 190 or 240 d of age, and heifers born in late spring (average birth date May 29 +/- 10 d) were weaned at 140 or 190 d of age. Heifers were managed to be first exposed to breeding at approximately 14 mo of age. After weaning, the calves were randomly assigned to treatments. Heifers on the constant gain treatment were fed a corn silage- and hay-based diet. Heifers on delayed gain treatments were placed on pasture but were fed grass hay or a supplement, or both, depending on the forage conditions. Three months before their respective breeding seasons, delayed gain heifers were moved to drylot and fed a corn silage- and barley-based diet (late winter or early spring) or moved to spring rangeland (late spring). The data were analyzed using mixed model procedures with calving system, weaning age, and postweaning management options creating 12 treatments. Average daily gain was 0.36 +/- 0.05 (SED) kg/d less (P < 0.001) for delayed gain heifers during the initial phase, whereas these heifers gained 0.44 +/- 0.03 kg/d more (P < 0.001) than constant gain heifers during the last 90 d before breeding. Body weights at the beginning of the breeding season did not differ (P = 0.97) between constant gain and delayed gain heifers but were affected by calving system and weaning age, reflecting some of the differences in initial BW. Prebreeding BW for heifers weaned at 190 d of age were 36 +/- 6.4 kg heavier (P < 0.001) for those born in late winter and early spring compared with late spring and were 388, 372, and 330 kg for heifers weaned in October at 240, 190, or 140 d of age (linear effect, P < 0.001). The proportion of heifers exhibiting luteal activity at the beginning of the breeding season was not affected (P = 0.57) by treatment. Approximately half of the heifers were randomly selected for breeding. Treatment had no effect (P = 0.64) on pregnancy rates. In conclusion, heifers from varied calving systems and weaning strategies can be raised to breeding using either constant or delayed gain strategies without affecting the percentage of heifers cycling at the beginning of the breeding season. These results suggest that producers have multiple options for management of heifer calves within differing calving systems.

Relationship between size of the ovulatory follicle and pregnancy success in beef heifers1

Previous research indicated that the size of the ovulatory follicle at the time of insemination significantly influenced pregnancy rates and embryonic/fetal mortality after fixed-timed AI in postpartum cows, but no effect on pregnancy rates was detected when cows ovulated spontaneously. Our objective was to evaluate relationships of fertility and embryonic/fetal mortality with preovulatory follicle size and circulating concentrations of estradiol after induced or spontaneous ovulation in beef heifers. Heifers were inseminated in 1 of 2 breeding groups: (1) timed insemination after an estrous synchronization and induced ovulation protocol (TAI n = 98); or (2) AI approximately 12 h after detection in standing estrus by electronic mount detectors during a 23-d breeding season (spontaneous ovulation; n = 110). Ovulatory follicle size at time of AI and pregnancy status 27, 41, 55, and 68 d after timed AI (d 0) were determined by transrectal ultrasonography. Only 6 heifers experienced late embryonic or early fetal mortality. Interactions between breeding groups and follicle size did not affect pregnancy rate (P = 0.13). Pooled across breeding groups, logistic regression of pregnancy rate on follicle size was curvilinear (P < 0.01) and indicated a predicted maximum pregnancy rate of 68.0 +/- 4.9% at a follicle size of 12.8 mm. Ovulation of follicles < 10.7 mm or > 15.7 mm was less likely (P < 0.05) to support pregnancy than follicles that were 12.8 mm. Ovulatory follicles < 10.7 mm were more prevalent (28% of heifers) than ovulatory follicles > 15.7 mm (4%). Heifers exhibiting standing estrus within 24 h of timed AI had greater (P < 0.01) follicle diameter (12.2 +/- 0.2 mm vs. 11.1 +/- 0.3 mm) and concentrations of estradiol (9.9 +/- 0.6 vs. 6.6 +/- 0.7) and pregnancy rates (63% vs. 20%) than contemporaries that did not exhibit behavioral estrus. However, when differences in ovulatory follicle size were accounted for, pregnancy rates were independent of expression of behavioral estrus or circulating concentration of estradiol. Therefore, the effects of serum concentrations of estradiol and behavioral estrus on pregnancy rate appear to be mediated through ovulatory follicle size, and management practices that optimize ovulatory follicle size may improve fertility.

Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2α, and progesterone1

We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F2alpha (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 microg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 microg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 microg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.

Resumption of postpartum luteal function of primiparous, suckled beef cows exposed continuously to bull urine1,2

The objective of this experiment was to determine if continuous exposure to bull urine alters resumption of ovarian cycling activity of primiparous, suckled beef cows. We tested the hypotheses that interval from urine exposure to resumption of luteal activity and proportions of cows that resume luteal activity by the end of the urine-exposure period do not differ between cows exposed to mature bull urine or steer urine. Thirty-eight Angus (A) x Hereford (H) cows, 4 mature A x H bulls and four 10-mo-old A x H steers, were used in this study. Cows were stratified by calving date, cow BW, calf BW, calf sex, dystocia score, and BCS; fitted with a controlled urine delivery device 2 wk before the start of treatments; and assigned randomly to be exposed continuously (24 h/d) to bull urine (n = 19) or steer urine (n = 19) beginning 40 d after calving. Urine was collected from bulls and steers every third day of the experiment. Blood samples were collected from cows starting on d 0 and every third day thereafter until the end of the exposure period (approximately 64 d). Likewise, controlled urine delivery devices were filled and refilled on the same schedule. Neither interval from urine exposure to resumption of luteal activity nor proportions of cows that resumed luteal activity during the urine-exposure period differed between cows exposed to bull urine or steer urine. We concluded that continuous exposure to mature bull urine does not affect resumption of luteal activity of primiparous, suckled beef cows.

Genetic partitioning of variation in ovulatory follicle size and probability of pregnancy in beef cattle1

The objectives of this research were to partition variation in ovulatory follicle size into genetic and nongenetic components and to assess the utility of ovulatory follicle size as an indicator trait associated with reproductive success in beef cattle. Data were collected during the years 2002 to 2005 from 780 beef females that ranged in age from 1 to 12 yr (mean of 2.4 observations per female). Data were analyzed with a multiple trait Gibbs sampler for animal models to make Bayesian inferences from flat priors. A chain of 500,000 Gibbs samples was thinned to every 200th sample to produce a posterior distribution composed of 2,500 samples. Heritability estimates (posterior mean +/- SD) were 0.16 +/- 0.03 for follicle size and 0.07 +/- 0.02 and 0.02 +/- 0.01 for pregnancy rate as a trait of the female and service sire, respectively. Posterior means of genetic correlations were all <0.10, with 0.00 contained within the respective 90% probability density posterior intervals. Results indicate that whereas follicle size is of greater heritability than pregnancy rate, its usefulness to improve reproductive rate is greatest as an ancillary phenotype in multiple trait selection.

Use of recombinant gonadotropin-releasing hormone antigens for immunosterilization of beef heifers1

The objectives of this study were to evaluate the effects of immunization against recombinant GnRH fusion proteins and growth promotants on onset of puberty, feedlot performance, and carcass characteristics of beef heifers. Heifers were immunized against an ovalbumin fusion protein containing 7 GnRH peptides (oGnRH, n = 12), a thioredoxin fusion protein containing 7 GnRH peptides (tGnRH, n = 12), a combination of oGnRH plus tGnRH (otGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant injected into the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk -2. Weekly blood samples were collected from wk -2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH-immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second booster injection, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from otGnRH heifers. During the 26-wk study, ovulation was prevented (P < 0.05) in 10 out of 12, 12 out of 12, 11 out of 12, and 0 out of 11 tGnRH, oGnRH, otGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH-immunized heifers than control heifers. Synovex H-implanted heifers had greater (P < 0.05) ADG from wk -2 to 26, greater LM area, and lesser percentages of KPH, yield grade, and quality grade than nonimplanted heifers, regardless of the immunization treatment. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented ovulation in 92% of the heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.

Calving system and weaning age effects on cow and preweaning calf performance in the Northern Great Plains1,2

A 3-yr study evaluated late winter (Feb), early spring (Apr), and late spring (Jun) calving systems in conjunction with varied weaning strategies on beef cow and calf performance from Northern Great Plains rangelands. Crossbred cows were randomly assigned to one of three calving systems (on average n= 168.calving system(-1).yr(-1)) and one of two weaning times (Wean 1, 2) within each calving system. The Feb and Apr calves were weaned at 190 and 240 d of age, whereas Jun calves were weaned at 140 and 190 d of age. Breeding by natural service occurred in a 32-d period that included estrous synchronization. Cows were managed throughout the year as appropriate for their calving season. Quantity and quality of hay and supplements were provided based on forage and weather conditions, physiological state of the cows, and available harvested feed resources within a year. After weaning, two-thirds of the early weaned steers were fed in confinement in Montana, and one-third were shipped to Oklahoma and were grazed or fed forage. One-half of the early weaned heifers grazed seeded pastures, and the other half was fed in confinement. Early weaned calves were weighed on approximately the same day as late-weaned calves. Birth weight and overall rate of gain from birth to weaning did not differ for calves from the three calving systems. Calf weaning weight differed by weaning age within calving system (P = 0.001), and calves from the Jun calving system that were weaned at 190 d of age tended (P = 0.06) to be lighter than calves of the same age from the Feb or Apr calving systems. Cow BW change and BCS dynamics were affected by calving system, but the proportion of cows pregnant in the fall was not. Cows suckled until later dates gained less or lost more BW during the 50 d between the first and second weaning than dry cows during this period. The previous year's weaning assignment did not affect production in the following year. Estimated harvested feed inputs were less for the Jun cows than for the Feb and Apr cows. We conclude that season of calving and weaning age affect outputs from rangeland-based beef cattle operations.