Emotional “Contagion” in Piglets after Sensory Avoidance of Rewarding and Punishing Treatment

TL;DR

This study shows that even when separated, untreated piglets can still feel the negative emotions of treated peers, suggesting emotional contagion in pigs.

Contribution

The study demonstrates that sensory avoidance does not prevent emotional contagion of negative emotions in piglets.

Findings

Untreated piglets showed synchronized heart rate changes with treated peers.

Negative emotions lasted longer than positive emotions in piglets.

Piglets in the punishing group showed more freezing behavior and less contact.

Abstract

In current pig farming, pigs are susceptible to stress-induced adverse emotions. Emotional contagion may propagate these emotions within a herd, potentially affecting overall welfare. Typically, treatments of individual pigs should be conducted separately from the group. Thus, after separation from treatment on an individual pig, the behavioral responses and heart rate changes of the companion pig were recorded to determine if the sensory avoidance was effective. It was found that peers were still affected by the treated pigs after sensory avoidance. Separation from treatment does not eliminate the effects of the treated pig on companion pigs, which can still be affected in post-treatment contact.

In the pig farming industry, it is recommended to avoid groups when treating individuals to reduce adverse reactions in the group. However, can this eliminate the adverse effects effectively? Piglets were assigned to the Rewarding Group (RG), the Punishing Group (PG), and the Paired Control Group (PCG). There were six replicates in each group, with two paired piglets per replicate. One piglet of the RG and PG was randomly selected as the Treated pig (TP), treated with food rewards or electric shock, and the other as the Naive pig (NP). The NPs in the RG and PG were unaware of the treatment process, and piglets in the PCG were not treated. The behavior and heart rate changes of all piglets were recorded. Compared to the RG, the NPs in the PG showed longer proximity but less contact behavior, and the TPs in the PG showed more freezing behavior. The percentage change in heart rate of the NPs was synchronized with the TPs. This shows that after sensory avoidance, the untreated pigs could also feel the emotions of their peers and their emotional state was affected by their peers, and the negative emotions in the pigs lasted longer than the positive emotions. The avoidance process does not prevent the transfer of negative emotions to peers via emotional contagion from the stimulated pig.

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