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Influence of Environmental Heat on Peripheral Plasma Progesterone and Cortisol During the Bovine Estrous Cycle¹

Department of Dairy Husbandry, Animal Science Research Center, University of Missouri, Columbia 65201

ABSTRACT

Plasma progesterone and Cortisol were measured in jugular blood by competitive protein-binding assay. Six cycling, estrus-synchronized Guernsey heifers were followed for four consecutive estrous cycles under two controlled temperature (18.2 C, 55% relative humidity; and 33.5 C, 55% relative humidity) conditions. Prolonged exposure to heat of Guernsey heifers increased plasma progesterone on days 2 to 19 of the first cycle and only on days 2 to 8 of the second cycle. However, heat stress depressed plasma Cortisol in both cycles and reduced the correlation coefficient between these steroids relative to specific stages of the estrous cycle.

¹ Contribution from Missouri Agriculture Experiment Station Journal Series No. 6923. Approved by the Director. The data reported here form part of a thesis presented by the senior author to the Graduate School of the University of Missouri in partial fulfillment of the requirements of the degree of Doctor of Philosophy.

² Department of Animal Science, UPLB, College of Agriculture, College, Laguna, Philippines; Department of Dairy Husbandry, University of Missouri, Columbia, Missouri; and Haryana Agriculture University, India, respectively.