333 Bull management: From sperm quality to herd fertility.

Abstract The bull plays a pivotal role in reproductive efficiency. Identifying strategies that can optimize semen quality and therefore herd fertility has great potential to improve the cattle industry. Artificial insemination (AI) gives the best measure of how semen quality can impact fertility since large numbers of females can be inseminated with a single ejaculate. The current standard dose for AI with conventional semen ranges from 10 to 40×106 sperm per dose. When 10, 20, and 40×106 sperm per dose were compared, there was no difference in pregnancy per AI (P/AI; P=0.31). However, P/AI was affected by the bull (n=5; P< 0.05; bulls A and B had greater P/AI than bulls C and E). Post-thaw analyses, semen quality evaluated by computer assisted sperm analyses (CASA) and flow cytometry were not able to effectively classify bulls according to their P/AI. In vitro sperm capacitation induced for up to 24 h was able to correctly identify bulls with greater P/AI as bulls with a greater (P< 0.0001) proportion of viable sperm, Zinc signatures 2 and 1 + 2, post-capacitation. Also, bulls with greater P/AI had a decreased (P< 0.0001) proportion of dead sperm positive for CD9 protein. These studies, however, were not able to differentiate bulls with intermediate fertility from high fertility. Bull management can not only directly impact semen quality but can also impact fertility when semen quality is not impacted. When subcutaneous fat was used to select bulls from a bull test, bulls that had increased subcutaneous fat (top 20%) had decreased percentage of morphologically normal sperm (P< 0.01) and were more likely to fail a breeding soundness examination (P=0.01) compared with bulls with lesser subcutaneous fat (bottom 20%). Bulls on a high gain (HG) diet, had greater subcutaneous fat (P< 0.01), compared to bulls on a maintenance diet but there were minimal effect on semen quality (increased acrosome damage; P=0.02), but following in vitro fertilization (IVF) there was no impact of diet on cleavage rate (P=0.94), but HG bulls had decreased (P=0.01) blastocyst rate (as percentage of cleaved embryos) compared to maintenance bulls. Brahman bulls exposed to pre-natal transportation stress (PNS) in utero, also had negative impacts on fertility without impacting semen quality or proportion reaching sexual maturity by 22-month-of-age (82%vs 82%; P=1.0). A weak tendency was observed for more controls bulls to reach puberty compared to PNS bulls (100%vs 82%; P=0.14), and using IVF to determine impact on fertility, PNS bulls had decreased blastocyst formation compared to control bulls (P=0.03). In summary, semen quality (sperm motility, morphology, viability, acrosome integrity, and capacitation status) can impact bull fertility, moreover, other bull management decisions (PNS and overnutrition) may cause fertility issues without impacting what is currently measured in a conventional semen analysis.