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

We estimated genetic and phenotypic correlations and heritabilities for temperament indicators in growing pigs such as fearfulness (i.e., vocal and physical withdrawal response to an approaching human while isolated in an arena; attempts to escape from a weigh crate); boldness (i.e., biting, following or nosing a human walking inside their home pen) and aggression (i.e., skin lesions). Our results indicate that the studied traits were heritable, and some of these traits could potentially be useful for genetic selection. Additionally, genetic correlations were observed between aggression and fear indicators; pigs with a higher count of skin lesions on their flanks, backs, hind quarters and rear legs 24 h post-mixing (i.e., likely subordinate pigs) tended to display more distress while in isolation in a weigh crate, and were less likely to willingly approach a human. The three boldness indicators were associated, indicating that pigs biting the observer were also those that followed and nosed the observer, suggesting a general increase in exploratory drive and/or a reduction in fearfulness in these animals. These findings suggest that selection to reduce lesions to the rear of the body could have a desirable impact on other important behavioral indicators.