PSVI-28 Influence of Ambient Temperature and Temperature-Humidity Index on a Measure of Semen Quality in Crossbreed Beef Bulls.

There is a growing interest in how environmental heat stress affects economically important traits in cattle, such as production, health, and fertility. For example, under heat stress, dairy cattle consume less feed, produce less milk, and fertility decreases, all of which result in economic loss. Furthermore, there is a negative correlation between milk production and heat tolerance; thus, selection for high milk production results in less heat tolerant animals. Compared to dairy cattle, less is known about the effect of heat stress on beef cattle. In contrast to dairy cattle, beef cattle spend most the year outside and thus must withstand environmental conditions regularly. To begin our investigation into the effect of heat stress on fertility, we are studying the effect of environmental conditions specifically on beef bull fertility. We examined the relationship between the average temperature-humidity index (THI) and average maximum ambient temperature during the week leading up to motility measurements from 170 bulls (Angus x Simmental crossbreed). Preliminary results show a positive correlation between the average THI and motility (r=0.16, p=0.045). Likewise, there is a positive correlation between the average maximum ambient temperature and motility (r=0.16, p=0.038). Our preliminary results suggest that THI and maximum ambient temperature affect variability in sperm motility measurements. To further investigate factors contributing to the variability in the beef motility data, we are currently conducting a genome-wide association study (GWAS) to identify genetic markers associated with motility using a population of 350 beef bulls. Our GWAS could reveal genetic variation that is associated with overall better motility, as well as better motility during periods of heat stress and therefore better fertility in beef bulls for the future.