Social genetic effects on feed intake in pigs: from feeding visits to total intake

Text Abstract Social genetic effects can substantially influence phenotypes in animals and plants and the study of them is of interest. Group housing in animals – for example, in pigs – provide an ideal framework for studying interactions among individuals. In animals, the genetic of social effects has been studied by simplifying the underlying interactions – for example, by assuming that all the individuals in the group contribute equally to the social environment. This homogeneous behaviour is not observed in real conditions. Here, we address this issue showing that identification of interacting individuals is feasible in pig behaviour during growth, and we propose a model that leads to more accurate modelling of social genetics. Our approach infers the strength of interaction via time interval between visits of animals to automatic feeders. This measure of strength was then used in a reaction norm model to evaluate the genetic determinism of social effects. We also build a framework to transform variance components estimated for a trait continuously measured, such as feed intake per visit, into variance of total or aggregated trait e.g. during the growth period. Including social effects improves the fitting of the models. Visit-based social interaction was highest at short time intervals, decreasing rapidly and becoming negligible after 80 seconds. Variance components for the aggregated trait – the total feed intake – support the contribution of the social interactions. Our approach allows more precise understanding of social effects through individual feeding events and a measure of interaction strength, and further translates these into in an aggregated phenotype of interest. Article summary Animals living in groups constantly interact with one another, and these interactions can influence their performance and behaviour. Conventional approaches often assume that all animals contribute equally to the social environment; however, it is not true in real conditions. In this study, we identified and measured interactions between pigs based on the time interval between their visits to automatic feeders. We incorporated this information into a genetic model to account for differences in the strength of social interactions. Our results show that social interactions are strongest when animals visit the feeder close together and can meaningfully affect overall feed intake during growth.