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

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Abstract
Two experiments with lactating Holsteins monitored time required for alterations in adrenal glucocorticoid output in response to injection of 200 IU of ACTH after exposure to increased density and social disruption. Cows in 2 replicates of 9 cows each were assigned randomly across age to either zero (control), 2-day, or 9-day exposure into a high density (3.96 m2 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 m2 lot space and .5 free stalls per cow) and social adjustment into a new herd. Mean integrated glucocorticoid responses for exposure were 161.6 .+-. 12.6, 158.2 .+-. 28.2, 227.7 .+-. 32.2, and 229.9 .+-. 40.3 ng/ml .+-. SD. 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.