Stimulus generalization: the inability of pigs to discriminate between humans on the basis of their previous handling experience

Abstract

Two experiments tested whether pigs, under handling conditions similar to those in the commercial industry, could discriminate between two humans on the basis of their previous experience with either one or both of these humans. In the first experiment, pigs were handled by one of two handlers and both handlers used predominantly negative or aversive physical interactions in handling pigs. In the second experiment, all pigs were handled by two handlers; however, the handlers differed markedly in the nature of their handling towards pigs. The handling treatments were imposed over a 6-week period in both experiments. To examine whether stimulus generalization had occurred, the approach behaviour of all pigs to both handlers in a standard human approach test was observed following the handling treatments. In both experiments there were no significant interactions between the handling treatments and the handler in the human approach test. Furthermore, there were no consistent differences between handled pigs in their behavioural responses to familiar and unfamiliar handlers in the test. Therefore, in situations in which pigs are briefly handled by one of two stockpersons in a predominantly negative manner or in which pigs are briefly handled by stockpersons who differ markedly in the nature of their behaviour towards pigs, pigs are likely to exhibit stimulus generalization as measured by their behavioural responses to humans. Thus, in similar handling situations, the behavioural response of commercial pigs to one handler is likely to extent to other humans.