The perception of humans by piglets: recognition of familiar handlers and generalisation to unfamiliar humans.

Humans are part of the environment of domestic animals and interact with them daily, providing a good basis for the study of interspecific relationships. Abilities to discriminate and recognise individuals form the basis of these relationships, and they are crucial skills for domestic animals, since individual humans can differ in their behaviour towards them. At the same time, with experience, animals may develop a general memory of humans and generalise their behaviour towards strangers. This study aimed to determine the extent to which weaned piglets can discriminate familiar humans and generalise their past experience when faced with unfamiliar humans. Forty-eight groups of three piglets were submitted to two consecutive 5-day conditioning periods of the same or opposite valence (positive and/or negative) given by one (A) or two (A then B) handlers. The reactivity of piglets to a motionless human and to an approaching human was measured before and after conditioning periods with unfamiliar and familiar handlers. Thereafter, piglets which received treatments with the two handlers A and B were subjected to a choice test between both handlers. The reactivity to an approaching human appeared to better reflect the past experience with familiar handlers since piglets clearly recognised them and adapted their behaviour accordingly. In contrast, reaction of piglets to a motionless human reflected their natural propensity to seek interaction, even after a negative experience. Although piglets were able to extend their memory of humans to an unfamiliar human through generalisation, many factors seemed to interact in this process, especially the complexity of the previous experience (inconsistent vs consistent) and the context in which piglets met the unfamiliar human (motionless vs approaching). We conclude that discrimination and generalisation processes of reactivity to humans do not simply rely on past interactions, but also depend on the context according to the degree of similitude with their past experience.