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

Department of Dairy Science, Louisiana Agricultural Experiment Station, Louisiana State University, Baton Rouge 70803

ABSTRACT

Data collected monthly for one calendar year from Holstein cows lactating under Louisiana 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 intermediate to hot season gave evidence of eosinophila, and in addition, 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.

¹ Department of Agriculture, Southeastern Louisiana University, Hammond 70401.

² Louisiana Cooperative Service, Louisiana State University, Baton Rouge 70803.