Do Domestic Pigs Acquire a Positive Perception of Humans through Observational Social Learning?

Abstract

The human-animal relationship is an important component of farm animal welfare. Previous studies have shown that allowing animals to observe the gentle handling of a conspecific reduces fear and increases their affinity toward humans, a phenomenon attributed to observational social learning. This study investigated whether pigs are able to positively perceive and interact with a human after observing a conspecific (i.e., demonstrator pig) receiving long-term gentle handling by a stockperson. We also investigated whether this social learning was biased by the demonstrator’s social rank. Our results show that the observer pigs’ behavior was indicative of a greater affinity toward the stockperson regardless of whether they observed a socially dominant or subordinate demonstrator pig receiving gentle handling. Furthermore, pigs observing the gentle handling of a demonstrator pig exhibited lower physiological stress when they were confronted by the stockperson compared to pigs who received only minimal human contact. This study could have relevance in intensive swine production systems, where stockpersons have limited time to positively interact with the animals. Regular positive handling of a small number of selected pigs could be a useful strategy for reducing fear and stress in large groups of pigs. Farm animals can perceive humans positively by observing another animal being positively handled. This study evaluated whether pigs acquire a positive perception of humans after observing either a high or low socially ranked conspecific receiving gentle handling. Seventy-five 21-week-old pigs were housed in 15 nursery pens (five pigs/pen) and randomly assigned to one of three pen treatments: Dominant Demonstrator Group (DDG), Subordinate Demonstrator Group (SDG) and Control Group (CG). Pigs from DDG and SDG observed a high and low socially ranked conspecific (“demonstrator”), respectively, while the demonstrator received gentle stroking and a sucrose solution for 10 min, twice a day for 5 weeks. Control group pigs received minimal human contact. Following treatment, the behavior and heart rate variability of non-demonstrator pigs were evaluated in response to a stockperson in an open-field test. Pigs from the DDG and SDG contacted the stockperson sooner (p < 0.001), spent more time investigating the stockperson (p < 0.05), accepted more stroking (p < 0.001) and exhibited a lower low/high frequency ratio (p = 0.015) compared to the CG. No differences in learning between the pigs from the DDG and SDG were found. These results suggest that pigs can learn to perceive humans positively through observational social learning, regardless of the demonstrator conspecific’s social rank.