Effect of Temperature-Season on Bovine Adrenal Cortical Function, Blood Cell Profile, and Milk Production

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Abstract
Data collected monthly for 1 calendar year from Holstein cows lactating under Louisiana (USA) ambient climatic conditions comprised a total of 264 cow-months. The year was divided into seasons of cool, intermediate and hot temperatures. The hot season elicited depressions in circulating corticoids and percent hematocrit. Leukocytosis was a response to increasing ambient temperature primarily accounted for by an increase in circulating neutrophils. Progression from the intermediate to the hot season gave evidence of eosinophilia, and a relative eosinopenia may have been induced by increased adrenal cortex activity. Milk production was depressed during the hot temperature-season and showed no significant relationship with corticoids of plasma. Rectal temperatures and respiration rates were indicative of heat stress in the hot temperature-season and gave significant negative correlations with circulating corticoid concentration.

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