Lateral bias in the domestic pig (Sus scrofa)

Lateralised motor behaviour can contribute to the study of animal welfare, with links to emotional processing, stress responses and personality. Lateral bias in the domestic pig, a species prone to poor welfare, has been subject to little scientific attention. This study therefore aimed to assess laterality in the form of side preferences in a population of farmed pigs, exploring for differences between the sexes and consistency in side preferences, both between measures and over time. Observations of side preference were recorded in fifty pigs across five measures: a snout use task, step-up task, detour task, tail curling and lying side. Snout use, step-up and detour side preferences were observed twice (3 and 6 weeks-of-age) to evaluate test-retest reliability. Pigs were significantly more likely to be ambilateral than side-preferent for both lying side and snout use at 6 weeks of age. By contrast, animals showed significant side-preferences at the level of the individual on the detour task at 6 weeks of age. Directional laterality index (LI) scores for snout use were positively correlated with those of the step-up task at 6 weeks of age, while strength of laterality index (ABSLI) scores for snout use at 4 weeks of age were positively correlated with the step-up task scores at 6 weeks of age. No other LI or ABSLI scores were significantly correlated. Findings pointed to good test-retest reliability, with animals demonstrating a significant positive correlation in the direction, although not strength, of their lateral biases for the snout use, step-up and detour tasks. A cluster analysis, employed to explore for individual lateralisation patterns across motor functions, revealed a leaning towards left-side preferences on animals' combined step-up and detour laterality scores. Male and female animals showed no significant difference in either the strength or direction of their side preferences for any of the tasks. Overall, the results from this study point to individual-level lateralised behaviour in the domestic pig for one measure. Findings reveal a lack of sex differences and consistency between tasks, but show stability in pigs' side preferences over time, at least in the short-term.