Development of a prototype genetic evaluation for teat and udder score in American Angus cattle

Improving traits related to teat size (TS) and udder suspension score (US) can have long-term benefits for the health and productivity of beef herds. Well-structured udders and teats contribute to better calf health and growth, through un-inhibited suckling as well as improved cow longevity and milk production. No genetic evaluation is currently available for these traits in American Angus; the aim of the study was to investigate and develop a prototype genetic evaluation for TS and US. Teat and udder suspension scores were subjectively assessed on the farm following the American Angus Association guidelines. After quality control, the final dataset comprised 41,914 complete scores recorded on 23,886 Angus cows. Scores ranged from 1 to 9 for both teat and udder with similar mean (SD) scores of 7.1 (1.6), respectively. A series of multi-trait, animal models (pedigree size of 154,330 individuals) between TS, US, and growth traits were run to estimate trait heritability and genetic correlations. TS and US were found to be moderately heritable (0.31 and 0.34, respectively) and highly repeatable (0.51 and 0.47, respectively). TS and US had a high genetic correlation (0.76) between them and generally low negative genetic correlations with birth weight, weaning weight (WW), yearling gain, and yearling height (0 to -0.19). Udder score was moderately genetically correlated to the maternal genetic component of WW (MILK; -0.24). Mimicking a standard American Angus evaluation, model prediction accuracies for TS and US were estimated for best linear unbiased prediction (BLUP) and single-step genomic BLUP (ssGBLUP) scenarios. Accuracies ranged from 0.39 to 0.61 indicating that the starting set of phenotypes and models is sufficient to produce an accurate national evaluation. ssGWAS found that TS and US are likely polygenic, with no large single nucleotide polymorphism effects noted. Angus breeders are encouraged to submit annual teat and udder scores on their cows, to continue to improve model accuracy and expedite genetic improvement for these traits.