THE EFFECTS OF AVERSIVELY HANDLING PIGS, EITHER INDIVIDUALLY OR IN GROUPS, ON THEIR BEHAVIOR, GROWTH AND CORTICOSTEROIDS

The influence of three handling treatments, imposed for 10 weeks from 15 kg liveweight, on the behaviour, growth, subsequent reproductive performance and free corticosteroid concentrations were studied in 60 female pigs. The pleasant treatment involved individually handling the pig in a pleasant manner (e.g. gentle stroking). There were two unpleasant handling treatments; one involved individually handling the pig in an unpleasant manner (e.g. brief shocking or brief slapping) whenever the pig failed to withdraw from the experimenter and the other involved handling the pig within a group in an unpleasant manner whenever the pig failed to withdraw from the experimenter. The individual handling treatments were imposed for 30 s day-1 for 5 days week-1 and the group handling treatment was imposed for 2.5 min day-1 for 5 days week-1. There were no differences between treatments in growth rates over the 10-week period; however, the pigs in the pleasant handling treatment had a higher (P < 0.01) growth rate in the first 5 weeks of the handling period than pigs in the two unpleasant handling treatments. The feed conversion efficiency of pigs in the pleasant handling treatment was also superior (P < 0.05) in the first 5 weeks. The pigs in the unpleasant handling treatments were more (P < 0.01) fearful of humans, as indicated by their approach behaviour to a stationary experimenter at 20 weeks of age, and those that were individually handled experienced a greater (P < 0.05) increase in their free corticosteroid response to humans at 24 weeks of age than did pigs in the pleasant handling treatment. There was no physiological evidence at 24 weeks of age that the pigs in the unpleasant handling treatments were chronically stressed. These results indicate that aversive handling of pigs, either as individuals or as members of a group, will adversely affect the growth performance of the young pig. The fact that there was no evidence that the unpleasantly handled pigs were chronically stressed and that some recent results in this area are contradictory are considered in the discussion.