Olfactory cues and pig agonistic behavior: evidence for a submissive pheromone

One hundred and two prepubertal pigs were used in two experiments to determine if adrenocorticotropin hormone (ACTH)-induced increase in submissive behavior could be mediated by odorous signals. In experiment one, urine was collected from pigs treated with either 0, 1 or 10 IU/kg ACTH. Urine from pigs given 1.0 IU/kg ACTH caused a trend for a rise in submissive behavior. Level of plasma cortisol from donor pigs correlated well (r = .92) with duration of submissive behavior in the tested pigs. In experiment two, urine from ACTH-treated pigs increased submissive behavior when sprayed in the air during late fight. Thus, ACTH-induced submissiveness may be mediated by a pheromone. These results fit the hypothesis that, in addition to visual cues, an olfactory cue (perhaps adrenal in origin) is released towards the end of a fight to signal submission. Aerosolizing urine from ACTH-treated pigs may have interfered with this pheromonal signal.