Genetic parameters for calf social dominance indicators derived from automated milk feeding records in American Holstein calves

Automated milk feeders (AMF) generate large-scale longitudinal milk feeding data in calves, providing a great opportunity for deriving the novel traits that may be included in cattle breeding programs. For group-housed dairy calves, genetic selection for social dominance could have important implications on improving animal welfare and health, optimizing management practices, and possibly improving cow performance through indirect genetic selection. In this study, we derived and estimated genetic parameters for 6 calf social dominance indicators using a dataset consisting of 4,164,960 AMF visit records from 8,632 American Holstein female calves, including 5,910 calves with genomic data for 64,767 autosomal SNPs. We also assessed the genetic relationship of the derived social dominance traits with 7 calf traits related to feeding, growth, and health. Variance components were estimated using the average-information REML method and the single-step genomic BLUP approach. We observed that the varied weightings of time intervals between 2 consecutive visits to AMF did not have a clear effect on the calculated social dominance phenotypes. Among the social dominance traits, David's score (DS), adjusted DS by chance (adjDS), Kondo-Hurnik index (KHI), and adjusted KHI by dominance probability (probKHI) were found to be moderately heritable with h² estimates (±SE) ranging from 0.180 ± 0.017 (DS) to 0.210 ± 0.018 (probKHI), whereas Elo-rating scoring and success index were lowly heritable or less robust to the varied weights of visit time interval. Furthermore, the heritable indicators (DS, adjDS, KHI, and probKHI) had moderate and positive genetic correlations with average milk consumption per visit and average number of daily unrewarded visits, and weak positive correlations with birth weight. All dominance traits evaluated were lowly or not genetically correlated with the number of treatment records for bovine respiratory disease before 60 d of age. Our findings contribute to understanding the genetic basis of social behaviors in dairy calves. Several dairy calf social dominance traits in American Holsteins were found to be heritable with substantial additive genetic variance. However, further studies need to be performed to identify potential genetic relationships with economically and socially relevant traits in breeding programs, such as health, welfare, and performance traits.