Development of a genetic evaluation for hair shedding in American Angus cattle to improve thermotolerance

Abstract

Background: Heat stress and fescue toxicosis caused by ingesting tall fescue infected with the endophytic fungus Epichloë coenophiala represent two of the most prevalent stressors to beef cattle in the United States, costing the beef industry millions of dollars each year. The rate at which a beef cow sheds her winter coat early in the summer is an indicator of adaptation to heat and an economically relevant trait in many parts of the U.S. Further, research suggests that early-summer hair shedding may be reflective of tolerance to fescue toxicosis, as vasoconstriction induced by fescue toxicosis limits the ability of an animal to shed its winter coat. Here, we developed parameters for routine genetic evaluation of hair shedding score in American Angus cattle and identified genomic loci associated with variation in hair shedding score via genome-wide association analysis (GWAA). Results:Hair shedding score was found to be moderately heritable (h2 = 0.34 to 0.40), with differing repeatability estimates between cattle grazing versus not grazing endophyte-infected tall fescue. Our results suggest modestly negative genetic and phenotypic correlations between a dam's hair shedding score (lower score is earlier shedding) and the weaning weight of her calf, one metric of performance. Together, these results indicate that economic gains can be made via the use of hair shedding score breeding values to select for heat tolerant cattle. GWAA identified 176 variants significant at FDR < 0.05. Functional enrichment analyses using genes within 50 Kb of these variants identified pathways involved in keratin formation, prolactin signaling, host-virus interaction, and other biological processes. Conclusions:This work contributes to a continuing trend in the development of genetic evaluations for environmental adaptation. The results of this work will aid beef cattle producers in selecting more sustainable and climate-adapted cattle, as well as enable the development of similar routine genetic evaluations in other breeds.3