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Thyroid Activity and Heat Production in Cattle Following Sudden Ambient Temperature Changes¹

University of Missouri, Columbia

Abstract

Six nonlactating Holstein cows were fitted with rumen cannulas to permit the control of feed intake. The animals were exposed to sudden changes in temperatures of 1, 18, 38 and 18° C, consecutively, and were kept at the changed temperature for at least a week. Thyroxine I¹³¹ disappearance rate (K), PBI, O₂ consumption and rectal temperature were measured daily. At 38° C. the K values were depressed significantly (P<.05) only after 60 hr. of exposure. Plasma PBI increased at 12 hr. and decreased significantly at 60 hr. Rectal temperature and thyroid indices (K and PBI) displayed inverse trends during exposure to heat. Metabolic rate tended to follow the trends of the K and PBI values during the hot period. At 1° C. the K values were significantly increased at 36 hr. and then gradually declined toward the 18° C. values. After 60 hr. of 1 ° C. exposure, plasma PBI had increased significantly. Rectal temperatures and metabolic rates were not significantly affected. These data provide evidence that thyroid function and metabolic rate are involved in the compensation stage of acclimation to the new environment.

¹ A contribution from the Missouri Agricultural Experimental Station. Journal Series No.4022. Approved by the Director.

² Department of Dairy Husbandry.