DEVELOPMENT OF SELECTION TOOLS FOR MALE FERTILITY IN BEEF CATTLE

Reproductive EPDs in beef cattle evaluation have been limited to SC and HP, and examination of genetic trends reveals some evidence for genetic improvement in reproductive performance of females in the last 5 years (AAA 2019a, RAAA 2019, AGA 2019). However, no publicly-accessible data exists to evaluate performance of males. Importantly, increases in SC genetic trend predate increases in HP genetic trend by approximately 25 years in the only breed that reports both SC and HP EPDs (SC increasing when HP was trending downward or flat until public release of the HP EPD in 2011), indicating a weak or nonexistent relationship between the two traits. Interest in a ranking system for male fertility in bulls has been expressed (Marshall 2011) and there is ample appeal in better understanding and identifying specific genetic variants that underlie male fertility (Taylor et al. 2018), but no current system exists to provide this information.Semen collections within the beef industry are costly and require strict adherence to quality specifications. The National Association of Animal Breeders (NAAB)/Certified Semen Services established semen quality standards for its members (Marshall 2011). Ramifications of poor semen quality weigh most heavily on the most intensively used AI sires, which often struggle to keep up with the demand for semen. BSEs are also collected using a standardized procedure. Currently, the BSE involves a physical examination including measuring height, weight, SC, and assessing the testicles and penile function. Some advanced facilities have begun performing disease testing and assessing sex drive and mating ability (Chenoweth 2002). An ejaculate is also collected to evaluate morphology and motility of the sperm (Whittier and Bailey 2009). When assessing morphology, technicians identify the percent normal sperm cells in an ejaculate (Whittier and Bailey 2009). Current BSE standards classify abnormalities by location: head, midpiece, or tail (BSE 2018).These data, along with data on AI conception, can be utilized to develop male fertility selection tools for the beef industry, which can also include genomic information to improve their utility for young animals. High-density SNP data have not been incorporated into genetic evaluation systems for the improvement of male fertility within the beef industry. In addition, genetic correlations between semen quality data and many performance, reproductive, and carcass traits that may enhance or detract from selection efforts to increase male fertility have yet to be estimated.The following specific aims will be used as guidelines to achieve the goals of this study:Evaluate the impact of specific semen quality and production phenotypes on conception rates and develop a prototype sire conception rate EPD in beef cattleProvide a suggested model for evaluation of male fertility in beef bulls utilizing semen quality metrics from AI studs and BSE evaluations of natural service siresIdentify and validate QTL and genetic variants predictive for male fertility component traitsEstimate genetic correlations between semen quality parameters and growth, reproductive and carcass traits