Genetic study of behavioral and pituitary-adrenocortical reactivity in response to an environmental challenge in pigs

The adaptive response to environmental challenges involves both behavioral and neuroendocrine adjustments, and genetic factors have been shown to partly determine the intra- and interspecific variability observed in stress responses. To gain access to the biological and genetic basis of this variability, differences in neuroendocrine and behavioral responses to a 10-min novel environment exposure were studied in Meishan (MS) and Large White (LW) pig breeds, as well as in their F1 (MS x LW), F1R (LW x MS), and F2 (F1 x F1) crossings. Different behavioral scores were recorded and blood was taken by venipuncture, before and after the test, to measure levels of stress hormones (adrenocorticotropic hormone: ACTH and cortisol). MS pigs exhibited low vocalization, locomotion, and defecation scores when compared to LW. F1s showed intermediate locomotion scores. The vocalization scores of F1s were not significantly different from the respective scores of their parental MS and LW breeds. The defecation scores in F1s showed that there was some degree of dominance in the MS direction. Basal and poststress cortisol levels were higher in MS, F1s, and F2 than in LW, suggesting the dominance of this trait. Basal ACTH levels did not differ between the genetic types, whereas LW displayed higher poststress ACTH levels than MS. Phenotypic correlations were analyzed in the F2 segregating cross to study a possible link between behavioral and neuroendocrine traits. All behavioral variables were intercorrelated with 3 levels of association. The correlations between vocalization and locomotion scores and poststress ACTH levels suggest that these measures reflect the level of reactivity to the environmental challenge, and that they may share a common genetic control.