9 Contributions of sire diet to pregnancy establishment in cattle

The first weeks of pregnancy represent a pivotal period for pregnancy establishment and have considerable implications to fertility and beef production efficiency. While fertilization rates are considerably high in beef cattle, early embryonic mortality occurs in a large proportion of females between fertilization and the first pregnancy diagnosis. Most research efforts to address early pregnancy loss in cattle have focused on female-related factors that influence embryonic mortality. However, research from other animal models has shown that in addition to its genetic contributions, sperm-derived factors are involved in many post-fertilization events, such as syngamy, cleavage, and epigenetic regulation of the developing embryo. Large-scale field fertility studies have shown differences in pregnancy rates between sires with similar sperm parameters based on industry-standard semen analyses. However, few studies have investigated the paternal contributions to early embryonic development in cattle. In rodents, embryos sired from obese fathers had reduced cleavage and blastocyst development rates compared with embryos sired from control fathers. While bull over conditioning is a common phenotype observed in the beef industry, the impact of paternal nutrition on embryo and conceptus development remains poorly understood in cattle. Our group has recently evaluated the effect of paternal high energy diets on semen parameters and embryo development during in vitro embryo production. When compared with a control treatment, bulls exposed to a highly anabolic diet had similar sperm motility, but partially decreased semen quality based on computer-assisted sperm analyses and flow cytometry, respectively. In addition, while a highly anabolic diet resulted in similar cleavage rates compared with a control diet, decreased blastocyst rates as a percentage of cleaved oocytes were observed in bulls fed a highly anabolic diet. These results corroborate with reports in other species; however, further research is required to better understand the contributions of paternal diets to conceptus development and pregnancy loss.