Abstract
In domestic species, studying human-animal interactions and their consequences on the establishment of a positive Human-Animal Relationship (HAR) would have applications for both improving animal welfare. Objectify the quality of a HAR requires information on several aspects of the animal biology and emotional states (spatial behaviour, physiological and cognitive states). Growing evidence show that acoustic features of animal vocalisations may be a indicators of emotional states. Here, we tested the hypothesis that the quality of vocal expression may indicate the quality of HAR. Thirty piglets were tamed thanks to regular interactions with an experimenter talking and physically interacting with them, three times a day from weaning; while 30 other piglets received only contact necessary for their good breeding. Two weeks later, we recorded behaviours and vocalisations produced in presence of the static experimenter for five minutes. The test was repeated two weeks later, after a period of conditioning using human presence and contacts as a reward for all piglets, supposed to lead to a positive human-piglet relationship for all piglets. As expected, taming led to an attraction toward the experimenter, and, after the conditioning, untamed piglets expressed a similar level of attraction than previously tamed piglets. Tamed piglets generally produced shorter grunts than untamed piglets. However untamed piglets expressed more flexibility in call structure when vocalising close to a human, with a decrease of grunt duration and an increase of pitch, frequency range and noisiness in their grunt. This differential effect of proximity in tamed and untamed piglets was attenuated after the conditioning during a standard reunion with a static human but remained over time when the human was providing additional positive contacts. Results suggest that first, changes in vocal structure are consistent with indicators of positive states in the presence of a human. Second, increasing familiarity and proximity between a human and a piglet may induce changes in the acoustic structure of their grunts. Third, a carrying human trigger more changes in vocalisation structure than by their presence only. We show that vocalisation structure may allow to assess the quality of human-pig relationship.
Competing Interest Statement
The authors have declared no competing interest.