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Effect of Adrenocorticotropin Injection and Stress on Milk Cortisol Content¹

Department of Dairy Science, University of Wisconsin, Madison 53706

ABSTRACT

The purpose of this study was to determine whether cortisol content of milk might objectively measure stress in lactating dairy cows. A procedure has been developed for measuring cortisol in milk samples by a combination of solvent extraction, chromatography, and competitive protein-binding procedures. cortisol is normally in cow's milk, and injection of 200 IU adrenocorticotropin into five cows caused an increase in concentration of cortisol in milk from 2.5 ng/ml to 8.7 ng/ml. The stress of shipping 39 cows by truck from one dairy to another also increased the concentration of cortisol in milk and decreased milk production. We correlated the concentration of cortisol in milk with the average concentration in blood during the interval of milk secretion. Under control conditions and after injection of adrenocorticotropin to increase circulating cortisol, the regression equations describing the transport of cortisol from blood to milk are nearly identical. These results are interpreted to indicate that the mammary gland is integrating the circulating concentration of cortisol, and, therefore, the cortisol concentration in milk reflects the average concentration in blood during the interval of milk synthesis. Because the secretion of cortisol into milk is one example of a more general phenomenon, a model is presented to describe the diffusion of materials across the mammary secretory cell and into milk.

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison.

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