Adrenal reactivity to ACTH age changes in silver foxes inheriting different defensive behaviors

We have studied the influence of selection for behavior in female silver foxes upon their adrenal reactivity to ACTH. It has been found that in the first year of life, in females from a population selected for domesticated behavior (tame), there is no differentiated adrenal response to different doses of ACTH. In wild females during the first year of life, varying strength of adrenal response to large and small doses of ACTH is noted. During the second year of life, the differential adrenal response to different doses of ACTH is improved in females of both behavioral groups; the reactivity of tame second-year females to small doses of corticotrophin surpasses that of wild second-year animals. It is concluded that during ontogeny in domesticated silver fox females there is a retardation in the establishment of an adequate response to ACTH by the adrenals, as compared to nondomesticated females.