Overnutrition of young bulls delays in vitro embryonic development and decreases embryo quality†.

Fertility is a significant determinant of productivity in the beef cattle industry and young bulls are often fed highly caloric diets to accelerate growth. However, the effects of such nutritional strategies on early embryonic development remain poorly described. We hypothesized that feeding young bulls a high-gain diet would compromise early embryonic development in vitro. Twenty-nine bulls (13 months of age) were fed a moderate (target average daily gain = 1.22 kg/day; n = 15) or high gain (target average daily gain = 1.81 kg/day; n = 14) diet for 114 days. The high-gain diet increased average daily gain, final body weight, and subcutaneous backfat thickness. Semen was collected and frozen from each bull after 114 d of treatment and used for in vitro fertilization. Semen from high-gain bulls reduced embryo cleavage and early blastocyst formation. Blastocysts from high-gain bulls had fewer blastomeres, altered inner cell mass to trophectoderm ratio, and increased apoptosis. In addition, time-lapse embryo culture indicated that semen from high-gain bulls tended to reduce embryo cleavage and development to morula and early blastocyst stages, and delayed temporal progression to morula and blastocyst hatching. Similarly, semen from high-gain bulls increased cytoplasmic fragmentation of blastomeres during the first three cleavage events. These findings indicate that overnutrition of young bulls produces semen that compromises embryo development and quality, highlighting the need to develop feeding strategies to optimize growth and reproductive potential in cattle. Overnutrition of young, growing bulls results in semen that delays embryonic development and decreases embryo quality.