Adrenal Glucocorticoid Response to Exogenous Adrenocorticotropin Mediated by Density and Social Disruption in Lactating Cows

Abstract

Two experiments with lactating Holsteins monitored time required for alterations in adrenal glucocorticoid output in response to injection of 200 IU of adrenocorticotropin after exposure to increased density and social disruption. First, cows in two replicates of nine cows each were assigned randomly across age to either zero (control), 2-day, or 9-day exposure into a high density (3.96 m 2 lot space and .67 free stalls per cow) group. Response curves indicated increased glucocorticoid output potential within 2 days. In another experiment, 16 cows were assigned equally to either zero (control), 1, 2, or 3 days exposure to higher density (2.97 m 2 lot space and .5 free stalls per cow) and social adjustment into a new herd. Mean integrated glucocorticold responses for exposure were 161.6 + 2.6, 158.2 + 28.2, 227.7 32.2, and 229.9 40.3 ng/ml + standard deviations. Days 2 and 3 differed from controls showing that adrenal response, as measured by glucocorticoids, occurs within 2 days. No differences in bacteriological status, somatic cell counts of quarter milk, or milk production were observed.