Search

Subfertility represents one major challenge to enhancing dairy production and efficiency. Herein, we use a reproductive index (RI) expressing the predicted probability of pregnancy following artificial insemination with Illumina 778K genotypes to perform single and multi-locus genome-wide association analyses (GWAA) on 2,448 geographically diverse U.S. Holstein cows, and produce genomic heritability estimates. Moreover, we use genomic best linear unbiased prediction (GBLUP) to investigate the potential utility of the RI by performing genomic predictions with cross validation. Notably, genomic heritability estimates for the U.S. Holstein RI were moderate (h2 = 0.1654 ± 0.0317–0.2550 ± 0.0348); while single and multi-locus GWAA revealed overlapping quantitative trait loci (QTL) on BTA6 and BTA29, including known QTL for daughter pregnancy rate (DPR) and cow conception rate (CCR). Multi-locus GWAA revealed seven additional QTL, including one on BTA7 (60 Mb) which is adjacent to a known heifer conception rate (HCR) QTL (59 Mb). Positional candidate genes for the detected QTL included male and female fertility loci (i.e., spermatogenesis, oogenesis), meiotic and mitotic regulators, and genes associated with immune response, milk yield, enhanced pregnancy rates, and the reproductive-longevity pathway. Based on the proportion of phenotypic variance explained (PVE), all detected QTL (n = 13; P ≤ 5e-05) were estimated to have moderate (1.0% < PVE ≤ 2.0%) or small effects (PVE ≤ 1.0%) on the predicted probability of pregnancy. Genomic prediction using GBLUP with cross validation (k = 3) produced mean predictive abilities (0.1692–0.2301) and mean genomic prediction accuracies (0.4119–0.4557) that were similar to bovine health and production traits previously investigated.

Two experiments were performed to determine whether administration of ergotamine tartrate altered embryo development (Exp. 1) and uterine competency to establish pregnancy (Exp. 2) in beef cattle. Animals were fed daily either 0 (CON) or 40 mug/kg body weight of ergotamine tartrate (ERGOT). Following a 30-d period on respective diets, animals in Exp. 1 were artificial inseminated at estrus (d = 0) and single embryo recoveries performed on day 7; whereas, animals in Exp. 2 received two frozen-thawed embryos on day 7. As an indicator of ergotamine effects, prolactin was decreased throughout both experiments in ERGOT compared to CON animals (p0.05). Furthermore, rectal temperature (RT) tended to increase during both experiments in ERGOT compared to CON (p= 0.06). In Exp. 1, embryo recovery (p=0.08) and the percentage of transferable embryos (p=0.09) tended to be greater for CON than for ERGOT. Percentage of embryos that developed to compacted morula or greater was increased for CON compared to ERGOT heifers (p0.05). In Exp. 2, pregnancy rates of transferred embryos did not differ between treatment groups. Thus, administration of ERGOT to simulate fescue toxicosis altered developmental potential of embryos, but does not appear to affect uterine competency to establish pregnancy.

Sixteen yearling bulls were utilized to investigate administration of ergotamine tartrate on semen parameters, fertilization, and endocrinology. Bulls were allotted to a control diet of cracked corn, corn silage, and soybean meal (CON, n = 8) or a diet supplemented daily with 40 microg/kg body weight of ergotamine tartrate (ET, n = 8). Blood samples, average daily gain, scrotal circumference and rectal temperatures were collected every 14 day. Semen samples were obtained every 60 day and evaluated for motility and morphology. Scrotal temperatures were obtained by thermography immediately before electroejaculation. Semen from a subset of bulls from each treatment was also evaluated for in vitro fertilization. Administration of ET increased rectal temperature and resulted in lower scrotal temperatures compared to CON bulls (P < 0.05). However, prolactin, scrotal circumference, testosterone, and semen motility and morphology did not differ between groups throughout the experimental period (224 day). Cleavage rates of embryos derived from in vitro fertilization (IVF) with semen of bulls, fed with ET, were reduced compared to CON (P < 0.05); however, development of cleaved embryos to blastocyst did not differ between treatments. In conclusion, extended exposure of bulls to ET appeared to reduce fertilization potential of sperm.