Play in pigs - it's more fun in a group
Last changed: 19 November 2019
Play is suggested as an indicator of good animal welfare. A new paper describes differences between individuals in their patterns of play, but also shows that when pigs are in a group, there is a group play dynamic. The study was carried out by researchers at the Swedish University of Agricultural Sciences and focused on groups of four pigs playing with two rope tug toys. The data on play behaviour were analysed using a novel clustering and statistical modelling approach.
When playing, animals show great variability in their patterns of play, with different sequences of play behavioural elements, which leads to them having different play styles. In this study using 9-week old pigs, different phenotypic characteristics were found that could be used to classify individuals. These were whether they were initiators of play or joined ongoing play bouts, and whether they were a solitary player or a social player. Just because a pig was more likely to take the lead in initiating play with the toy, it didn't necessarily keep on playing when another pig joined. Not surprisingly, the characteristics of the group play were influenced by the characteristics of the four pigs in the group, for example a pig motivated for solitary play seemed to limit the play behaviour of the group as a whole. Nevertheless, a high level of synchronised playing, with 2, 3 or 4 pigs playing together much more often than expected by chance, supports the view that juvenile play behaviour in pigs is group-driven. "It may be fun to play with an object alone," says Manja Zupan, "especially if you are a solitary individualist, but is more fun playing together with others."
What is new about this study is the novel application of statistical methodology to behaviour data. Two methods were applied to analyse complex state sequences; the cluster analysis and the statistical modelling of sequence data. It was this statistical approach that allowed to demonstrate that individual decisions of what play type to perform or for how long to play are strongly influenced by communal decisions.
When looking at the transitions in state sequences (i.e. transitions from one type of play to another) researchers found that groups of pigs had a significantly different development of play during the 30 min test which was not under the influence of the relative balance of initiators or joiners in the group. By showing that within the group the pigs had mainly the same play patterns suggests a democratic group decision-making mechanism. Maintaining proximity and showing synchronised behaviour, such as during play, allows animals to exchange information about their emotional states continuously.
Improved understanding of the details of play can contribute to our understanding of the evolutionary significance of play and perhaps how better to stimulate play behaviour in commercial pigs so contributing to increased welfare.
Reference
Zupan, M., Rehn, T., de Oliveira, D. et al. Individual play patterns stimulated by a familiar object are group-driven. Sci Rep 9, 6092 (2019) doi:10.1038/s41598-019-42382-9