Increasing reproductive efficiency and progeny performance through improved embryonic and genetic selection in cattle

A series of studies were completed to determine if reproductive efficiency and offspring performance could be improved through the implementation of a novel method of embryonic selection and the proliferation of a desirable genotype in cattle. The first study evaluated the effectiveness of an Embryo Chamber to distinguish between viable and nonviable bovine embryos based on specific gravity of the embryo. In this study, 19 in vitro produced (IVP) and 15 in vivo derived (IVD) Grade 1 embryos were individually placed into a 0.5 mL semen straw of media and allowed to descend through the Embryo Chamber. Descent time through a vertical, one-centimeter timing region was recorded, and embryos were removed from the chamber and either transferred into recipient females or cryopreserved and transferred at a later date. In order to determine if Embryo Chamber evaluation had an effect on pregnancy status, 27 IVP and 12 IVD, Grade 1 embryos that were not evaluated with the Embryo Chamber were also transferred into recipient females at the time of project embryo transfer. Pregnancy was later determined via rectal ultrasound and recorded. There was no significant difference in conception rates between embryos evaluated with the Embryo Chamber and those not evaluated with the Embryo Chamber, indicating that chamber analysis had no negative impact on viability of both IVP (P = 0.54) and IVD (P = 0.93) embryos. Of the 34 total embryos evaluated with the Embryo Chamber, 22 resulted in successful implantation and pregnancy, with 13 pregnancies (68.4%) by IVP embryos and 9 (60%) by IVD. There was no difference in average descent time of pregnant and non-pregnant embryos for IVP (P = 0.54) or IVD embryos (P = 0.24). When divided into groups according to descent time, 32% of all observations for IVP embryos occurred between 30 to 50 s with a 66.7% conception rate, and 42% occurred between 70 to 90 s with a 75% conception rate (P = 0.85). For IVD, 60% of all observations occurred between 90 to 110 s, with a conception rate of 66.7% (P = 0.35). Analysis of the correlation between descent group and pregnancy outcome or descent time and pregnancy outcome showed no strong correlation for either production method. Though not significant, the trends highlighted in this data lend support to previous research with variations of the Specific Gravity Device. Further research is needed to thoroughly evaluate the potential of this technology as a method of noninvasive assessment of embryo quality. The second study evaluated the merit of an F1 USDA Prime, Yield Grade 1 carcass clone sire as a terminal sire in the beef x dairy production system. In this study, the clone sire, AxG1, and a purebred Angus reference sire, Foundation, were bred to dairy cows (n = 1,430) at a commercial Jersey dairy in the Texas Panhandle. Performance data from resulting offspring of these matings was collected and analyzed to assess differences in performance between the two sires. Post-partum dam data was also collected to determine if there were any negative impacts of sire on the subsequent reproductive performance of the dams. Conception rates were 39% for AxG1 and 30% for Foundation (P < 0.01), and average gestation length was 284 d for AxG1 and 280 d for Foundation, respectively (P < 0.01). Calves sired by Foundation reported a lower average birth weight than those sired by AxG1 (32.62 and 35.00 kg; P < 0.01), with no difference in calving ease score (P = 0.24). Calves sired by AxG1 were heavier than Foundation calves at 60 d (72.46 and 72.01 kg; P < 0.01), with no difference in weight at 120 d (108.03 and 108.12 kg; P = 0.97). However, calves sired by Foundation had significantly higher average daily gains from 0 to 60 d (P = 0.09) and tended to have higher gains from 0 to 120 d (P < 0.01). Sire had no effect on total morbidity (P = 0.25) or mortality (P = 0.15), while also having no significant impact on post-partum reproductive performance of dams. These data suggest that AxG1 performed comparably as a terminal sire when mated for beef x dairy composite production.