When animals engage in 'non-serious' fighting (play-fighting) they 'borrow' motor patterns especially from the aggressive context. It may be difficult to distinguish play- and real-fighting. This is particularly true for piglets (Sus scrofa), which can use play-fighting as a substitute for aggression. To check for the structural differences between play- and real-fighting in piglets, we: i) video recorded 496 interactions from three litters (at Parva-Domus extensive ethical farm; Turin, Italy); ii) extracted (by video analyses) duration, patterns, and data on involved individuals; iii) calculated session structural/ecological indices; and iv) compared the indices (play- vs real-fighting). Compared to real-fighting - play-fighting was longer (informing its rewarding nature), more symmetrical (lower asymmetry index) and variable (higher Shannon index). Moreover, play-fighting showed less pattern repetition (lower Repetition Index) and was not more polyadic and evenly distributed (comparable polyadic and Pielou indices). By being longer, and more variable and symmetrical than real-fighting, play-fighting could serve some of its functions such as motor training, social assessment and training for the unexpected. However, play-fighting in piglets did not comply with all the expected play features, possibly because play is a fluid behavioural system that under certain circumstances may escalate into or replace aggression.
Keywords: Aggression; Asymmetry index; Domestic pig; Pielou evenness index; Play; Shannon variability index.
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