(217) Semen of Young Bulls Fed a High-Gain Diet Delays Embryonic Development and Decreases Embryo Quality In Vitro

Arslan Tariq¹; Lucas M. Gonclaves²; Tatiane S. Maia¹; Quinn A. Hoorn¹; Dylan B. Davis²; Saulo M. Zoca³; R. Lawton Stewart Jr.²; Pedro L.P. Fontes²; John J. Bromfield¹

¹ Department of Animal Sciences, University of Florida, Gainesville FL, USA.

² Department of Animal and Dairy Science, University of Georgia, Athens GA, USA.

³ Department of Animal Science, University of Tennessee, Knoxville TN, USA.

Abstract Text:

Fertility is a limiting factor in the beef cattle industry. Young bulls are often raised on high-gain diets to enhance average daily weight gain, hasten puberty, and maximize market value. The effects of such nutritional strategies on future fertility are poorly understood. We hypothesized that feeding young bulls a high-gain diet would compromise in vitro fertility. A total of 29 bulls (13 months of age) were stratified by body weight and fed the same diet for 114 d to achieve a low-rate of gain (1.22 kg/day; n = 15) or a high-rate of gain (1.81 kg/day; n = 14). Final body weight, average daily gain, and subcutaneous fat thickness were greater in bulls fed the high-gain diet compared to the low-gain diet (87.3 kg, 0.8 kg/d, 2.3 mm respectively). At the end of the feeding period, semen was frozen and used for in vitro fertilization. Initially, a total of 3,458 bovine cumulus-oocyte complexes were matured in vitro for 22 h and fertilized in nine individual replicates for each bull. Putative zygotes were evaluated for cleavage on d 3.5 and blastocyst development on d 6, 7, and 8. Blastocysts were collected on d 7 to assess cryosurvival, or on d 8 to evaluate blastomere number, lineage, and apoptosis. Semen of high-gain bulls reduced oocyte cleavage on d 3.5 by 6.5%, decreased the percentage of oocytes developing to blastocyst stage embryos on d 6 by 4.7%, and tended (P ≤ 0.10) to reduce blastocyst development on d 7 by 4.5%. Semen of high-gain bulls reduced the total number of blastomeres, increased the inner cell mass to trophectoderm ratio and increased apoptosis of blastocysts but did not affect cryosurvival. Furthermore, semen of six bulls with the greatest disparity in subcutaneous fat thickness were used to fertilize 252 cumulus-oocyte complexes which were then cultured individually in a time-lapse incubator to evaluate developmental morphokinetics for 190 h post-fertilization. Semen of high-gain bulls tended (P ≤ 0.10) to reduce the proportion of oocyte that underwent the first, second and third cleavage events and the proportion of oocytes to develop to morula, early blastocyst, and blastocyst. Semen of high-gain bulls tended (P ≤ 0.10) to delay the temporal development of embryos to morula by 15.6 h or hatched blastocyst-stage by 6.7 h. The proportion of highly fragmentated cleaved embryos was greater for high-gain bulls compared to low-gain bulls by 32%. These findings suggest that feeding a high-gain diet to young bulls results in semen that delays embryonic development and decreases embryo quality. It is imperative to determine the best dietary regime to raise young bulls to maximize growth, marketability and fertility.