128. Award Talk: Heritability and Repeatability of Hair Shedding in Angus Beef Cattle.

Abstract Hair shedding is an adaptive trait in beef cattle that influences thermoregulation and overall physiological performance. Cattle that shed their winter coat efficiently are better able to dissipate heat during warmer months, which can reduce heat stress and improve productivity and welfare. In environments where cattle face climatic challenges, including high-elevation, cold conditions, thermoregulatory efficiency may also influence performance in other ways. The objective of this study was to estimate the heritability and repeatability of hair shedding scores in Angus cattle. Hair shedding records from 34,680 purebred Angus cattle were obtained from the American Angus Association. The pedigree file included 207,694 animals, of which 25,122 were genotyped. In total, the dataset contained 51,628 hair shedding records. Because hair shedding can be measured multiple times on the same animal, the trait was analyzed using a repeatability model. Fixed effects were defined through contemporary groups composed of herd, sex, calving season, toxic fescue indicator (yes/no), producer-supplied management group code, age group by year, and scoring group to account for environmental and management differences within the group scored together. Variance components were estimated using three quantitative genetic models: pedigree-based BLUP (BLUP), which incorporates only the pedigree numerator relationship matrix; genomic BLUP (GBLUP), which uses the genomic relationship matrix; and single-step genomic BLUP (ssGBLUP), which integrates both pedigree and genomic relationship information into a single analysis. Heritability estimates for hair shedding were 0.47 ± 0.01 using BLUP, 0.39 ± 0.008 using GBLUP, and0.47 ± 0.008 using ssGBLUP. Repeatability estimates were 0.53 ± 0.006 for both BLUP and GBLUP and 0.54 ± 0.0002 for ssGBLUP. These estimates indicate that hair shedding is a moderately to highly heritable trait and that animals tend to express consistent shedding patterns across repeated observations. In conclusion, the moderate to high heritability estimates obtained across the three evaluation methods indicate that a substantial proportion of the phenotypic variation in hair shedding is explained by genetic differences among animals. The consistently high repeatability estimates suggest that hair shedding scores are stable across repeated observations within individuals, supporting the reliability of this phenotype for genetic evaluation. Together, these results demonstrate that hair shedding can respond effectively to selection and may serve as a useful indicator trait for improving thermoregulation and environmental adaptation in beef cattle populations.