Relationship between behaviour and adrenocortical response pattern in domestic pigs

Abstract

Large individual differences in pigs' behavioural and adrenocortical responses to stressful conditions is a common problem. This study examines the existence of stable differences between individuals and the relationship between behaviour and adrenocortical function. Behavioural activity in the home pen, open-field behaviour, and adrenocortical response to ACTH 1–24 were studied in 24 domestic pigs at different ages. Individual variation of behavioural and physiological responses was large; the amount or intensity of both responses remained consistent over the 14 week study period within pigs; variation between littermates in both responses was minimal. Further analysis revealed that pigs that showed a greater response to adrenocortical stimulation were more active and vocalized more during the open-field test and were less active in their home pen than less responsive pigs. We conclude that the responsiveness of the adrenal cortex in pigs is associated with increased locomotor activity and vocalization in response to the novel situation. The increased locomotor activity and vocalizations of hyperresponsive pigs in an open field are indicative of their excitability and are often accompanied by escape attempts. Moreover, those animals are characterized by less behavioural activity under unstimulated conditions. The results support the concept that adrenocortical function is positively correlated with locomotor behaviour and vocalization score in an open field and that differences in adrenal function are consistent within individuals.