Pig behaviour study uncovers surprises

British researchers find that levels of play fighting in young pigs did not differ between the socialized and control groups

Research into pig behaviour carried out at Queen’s University in Belfast, Northern Ireland, has come out with some surprising findings.

The research team at the Institute for Global Food Security (IGFS) at the university described the results as “intriguing” and “unpredicted.”

It also found gender differences in the social-play behaviour of young pigs, with links to aggression later in life.

Researchers investigated two sets of piglets. The first group was 12 litters of piglets that could interact freely with non-litter mates in an adjacent pen, termed as socialization. The second group was 12 control litters, maintained in their own pen.

Researchers found, contrary to what was expected, that levels of play fighting did not differ between the socialized and control groups.

However, males conducted higher levels of play fighting than females.

Research lead Dr. Gareth Arnott and doctoral student Jennifer Weller, based at IGFS, suggested this reflected the development needed for pigs’ later-life social environment.

This differs between the sexes, with adult wild boars engaging in escalated fights to gain access to groups of females.

In addition, researchers examined links to later-life aggression, an important welfare concern in pig farming. Surprisingly, pigs socialized in early life were found to more quickly attack an “intruder” pig introduced to the home pen.

Researchers suggested this could be attributed to the ability of socialized individual animals to more rapidly assess a dominance hierarchy compared to their non-socialized counterparts, possibly mediated by the experience of interacting with a greater range of play partners.

As well, there was an unexpected gender effect. Females that showed higher levels of early-life play fighting attacked more quickly in the intruder test. In males, there was no correlation evidenced between early play fighting and later aggression.

In the wild, female pigs live in groups, while males are more solitary, which may incline females to being more attuned to group structures and pecking orders.

“Ultimately, we need more research in this area as there are still a lot of knowledge gaps, hypotheses and assumptions around early play in animals,” said Arnott.

“We’ve uncovered something interesting and confounding, not only around the influence of early play, but also the role of sex, which has been, to date, relatively overlooked.”

The research team is now examining links between play experience and later-life dominance, and assessment ability during aggressive encounters.

The study was published in the journal Scientific Reports, part of the Nature group of publications.

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