Genetic associations between human-directed behavior and intraspecific social aggression in growing pigs

This study estimated the genetic parameters for human-directed behavior and intraspecific social aggression traits in growing pigs, and explored the phenotypic correlations among them. Data on 2,413 growing pigs were available. Pigs were mixed into new social groups of 18 animals, at 69 ± 5.2 days of age and skin lesions were counted 24 h post-mixing. Individual behavioral responses to isolation in a weighing crate or when alone in an arena while a human directly approached them were assessed within 48 h post-mixing. Additionally, pigs were tested for behavioral responses to the presence of a single human observer walking in their home pen in a circular motion within one and 4 wk post-mixing noting pigs that followed, nosed, or bit the observer. Animal models were used to estimate genetic and phenotypic parameters for all studied traits.

Heritabilities (h²) for skin lesions, isolation in a weighing crate, and approached by a human responses were low to moderate (0.07 to 0.29), with the highest h² estimated for speed of moving away from the approaching observer. Low but significant h² were estimated for nosing (0.09) and biting (0.11) the observer at 4 weeks post-mixing. Positive high genetic correlations (r_g) were observed between isolation in a weighing crate, and approached by a human responses (0.52 to 0.93), and within skin lesions traits (0.79 to 0.91) while positive low to high correlations between the estimated breeding values (r_EBV) were estimated within the human walking in pen test (0.24 to 0.59) traits. Positive moderate r_g were observed between isolation in a weighing crate and central and posterior skin lesions 24h post mixing. The r_EBV of isolation in a weighing crate and approached by a human test responses and human walking in pen test traits were low, mostly negative (−0.21 to 0.05) and not significant. Low positive r_EBV (0.06 to 0.24) were observed between skin lesions and the human walking in pen test traits. Phenotypic correlations between isolation in a weighing crate and approached by a human responses and skin lesions or human walking in pen test traits were mostly low and not significant.

Under the conditions of this study, h² estimates for all studied traits suggest they could be suitable as a method of phenotyping aggression and fear/boldness for genetic selection purposes. Additionally, genetic correlations between aggression and fear indicators were observed. These findings suggest selection to reduce the accumulation of lesions is likely to make pigs more relaxed in a crate environment, but to alter the engagement with humans in other contexts that depends on the location of the lesions under selection.

Suzanne Desire et. al. Genetic associations between human-directed behavior and intraspecific social aggression in growing pigs. Journal of Animal Science. 2023; 101:skad070. https://doi.org/10.1093/jas/skad070