Sows' Responses to Piglets in Distress: An Experimental Investigation in a Natural Setting

Simple Summary Maternal behaviour is a common trait in many mammalian species, and mothers can invest a lot of energy in parental care, ensuring a higher probability of survival for their infants. An interesting question is whether these behaviours are influenced by particular mechanisms and how the offspring can effectively attract the mother's attention. In order to try to answer this question, we studied a group of sows reared in northern Italy (ethical farm Parva Domus, Cavagnolo, Turin) in which lactating and non-lactating females were present. Isolation calls emitted by the piglets were able to generate a state of anxiety in the mothers and can be therefore a valid example of a useful mechanism to request maternal care effectively. Furthermore, we not only observed that lactating females responded and reacted more to the vocalisations of piglets from other broods, but also that less aggressive mothers responded more. Finally, we found that certain vocalisation characteristics may influence the type of response by the mothers. Therefore, several factors seem to play a key role in eliciting response behaviour in sows. Domestic pigs (Sus scrofa) possess complex socio-cognitive skills, and sows show high inter-individual variability in maternal behaviour. To evaluate how females-reared under natural conditions-react to the isolation calls of their own piglets or those of other females, we conducted observations and experimental trials. In January-February 2021, we conducted all-occurrences sampling on affiliation, aggression, and lactation (daily, 7:30-16:30 h) on six lactating and four non-lactating females at the ethical farm Parva Domus (Turin, Italy). The trials (30 s each, n = 37/sow) consisted of briefly catching and restraining a piglet. We recorded the sow response (none/reactive/proactive movement towards the piglet; self-directed anxiety behaviours such as body shaking) before and during the trial and under control conditions. Increased levels of anxiety behaviour in sows were accompanied by an increased frequency of responses. Less aggressive sows and lactating sows showed the highest frequencies of response. Finally, the isolation calls' maximum intensity had an influence on the type of response observed, with higher proactive response frequencies following lower intensity isolation calls. Our results suggest that being under lactation could play a key role in increasing sow response levels and that specific acoustic features may influence the response.