Conditioned approach-avoidance responses to humans: the ability of pigs to associate feeding and aversive social experiences in the presence of humans with humans

Abstract

Since there is a number of common industry husbandry procedures conducted by stockpersons that may have rewarding or aversive elements for pigs, pigs may learn to associate these rewarding or aversive elements of a procedure with the handler conducting the procedure. Therefore, because of this second-order conditioning, changes in the behavioural response of pigs to humans may limit the productivity and welfare of pigs through a stress response. Experiment 1 was conducted to examine whether sexually unreceptive female pigs regularly introduced to boars in their accommodation pens for oestrus detection learn to associate the aversive elements of this procedure with the experimenter conducting the procedure. Experiment 2 was conducted to examine whether pigs fed by an experimenter learn to associate the rewarding elements of this procedure with the experimenter conducting the procedure. Two other treatments were imposed in each experiment as controls: a treatment in which pigs received human contact similar to that in the husbandry procedure, and a treatment in which pigs received minimal human contact. To examine whether gilts learnt to associate the rewarding or aversive elements of the procedures with the presence of humans, the approach behaviour of all pigs to the familiar experimenter and an unfamiliar experimenter was observed in a standard human approach test at the end of each experiment. In Experiment 1 the apparent aversive experiences associated with introduction to boars in a confined area had no effects ( P > 0.05) on the subsequent approach behaviour of the pigs to the experimenter in the standard test conducted after 5 weeks of treatment. In Experiment 2, pigs that were fed in the presence of the experimenter were quicker ( P < 0.05) to closely approach the experimenter in the standard test conducted after 6 weeks of treatment. Furthermore, in both experiments there was no difference in the approach behaviour of handled pigs to the familiar and unfamiliar experimenters. The results indicate that pigs associate a rewarding experience of feeding with the handler and that this conditioning results in pigs being less fearful of the handler and other humans. In contrast, pigs receiving frequent positive handling failed to associate the aversive elements of an oestrus detection procedure with the handler.