Changes in serum cortisol reveal functional differences in frustration-induced chain chewing in pigs

Abstract

The pituitary-adrenal correlates of oral stereotypies in pigs were studied in two frustration situations, a situation of intermittent food distribution in which small amounts of food were given every 4 min (n=4), and a massed food situation in which the same total amount of food was given in one meal at the beginning of the session (n=5). Control animals (n=6) were exposed to intermittent food but without a chain. Both intermittent-food and massed-food pigs developed chain chewing at similarly high rates. Blood samples were taken on days 8 and 21 of the experiment. Serum cortisol decreased between the beginning and the end of session 21 in intermittent-food pigs, but increased in pigs subjected to the massed-food condition. These findings suggest that oral stereotypies elicited by an intermittent schedule of food presentation are not equivalent to those elicited by the massed-food regimen.