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Performance Line Developing Genetic Selection Tools for Male Fertility By Tonya Amen, National Center for Beef Excellence Fertility is the most economically important trait in beef cattle, however, only recently have we begun to develop selections tools for female fertility. Since one bull may be used to breed numerous females via natural service and even more through AI, fertility may be more important in a specific bull than in a specific cow, yet male fertility has been virtually ignored in terms of development of genetic selection tools. According to Katselic et al (2012), few bulls are completely sterile, but in an unselected population, 20 to 40% may have reduced fertility. This provides excellent opportunity to address fertility from the male standpoint. Sub-fertile bulls can cause all kinds of issues that impact your bottom line and just a few of these include reduced weaning weights (due to longer calving seasons that result from delayed conception), increased culling rates and increased risk of injury to bulls and cows as the result of repeated breeding. According to Dr. Megan Rolf, “I think we have a hole in our genetic evaluation systems relative to fertility and we don’t currently turn in any of the data we already collect that could be used to help build selection tools for male fertility. Though we have focused on female fertility, the heritability on male fertility traits actually appears to be higher than for female fertility. So, we could arguably address male fertility more easily than female fertility if we can turn in enough high-quality data on the appropriate traits to build the selection tools.” With this in mind, the North American Limousin Foundation has agreed to collaborate on a project with a team of researchers from Kansas State University to investigate the important trait(s) of male fertility. LIMOUSIN Today | 29