150 Effects of managing mature beef bulls on divergent planes of nutrition on novel measures of bull fertility

Abstract

Abstract Fifteen mature beef bulls (BW = 800.4 ± 17.4 kg) were used in a 112-d experiment to evaluate effects of divergent planes of nutrition on novel measures of bull fertility. Bulls were ranked by BW and randomly assigned to one of two treatments: 1) managed on a positive plane of nutrition (POS, n = 8), or 2) managed on a negative plane of nutrition (NEG, n = 7). Bulls were individually fed a common diet adjusted biweekly to achieve targeted weight loss or gain of 12.5% of original BW. On d 112, electroejaculation was used to collect 2 ejaculates from each bull, which were combined, extended, and frozen. The Guava easyCyte 8HT Flow Cytometer was used to analyze cell membrane and acrosome integrity, mitochondrial energy potential, and oxidation status of frozen-thawed semen. Data were analyzed for effects of treatment with bull as the experimental unit using the MIXED procedure of SAS. By design, bull BW diverged (P < 0.0001) with POS bulls gaining 1.27 ± 0.08 kg/d, whereas NEG bulls lost 0.91 ± 0.08 kg/d. Treatment did not influence cell membrane integrity (P = 0.20), or proportion of live sperm with intact acrosome (P = 0.91). A greater (P = 0.04) proportion of sperm from POS bulls (35.1 ± 3.47%) were alive and stained reactive oxygen species positive compared with sperm from NEG bulls (23.8 ± 3.71%) indicating sperm from POS bulls was more prepared to withstand oxidative stressors. However, NEG bulls (27.2 ± 5.22) had a greater (P = 0.01) proportion of sperm with polarized mitochondrial energy potential compared with POS bulls (6.1 ± 4.89%), indicating greater energy for sustained motility. We conclude that plane of nutrition during spermatogenesis may impact sperm’s ability to withstand stressful environments encountered and to sustain motility in the female reproductive tract after cryopreservation.