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Some Blood Constituents of Dairy Cattle: Influence of Thyroxine and High Environmental Temperature¹

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

Studies of alterations in the blood composition of dairy cattle due to thyroxine injection and environmental heat exposure were made to evaluate metabolic changes associated with hormonal changes in warm climatic environments. This report indicates that at 18 and 32 C L-thyroxine increased significantly the following blood parameters—hematocrit (< .001), thyroxine I¹³¹ disappearance rate (< .05), acetate (< .05); whereas phosphorus was decreased (< .05). Thyroxine did not affect either the total nitrogen, creatine, creatinine, protein-bound iodine, magnesium, or sodium. The high environmental temperature (32 C) decreased significantly hematocrit (< .001), protein-bound iodine (< .05), acetate (< .10), and magnesium (< .001), increased creatinine and phosphorus (< .05) and did not affect total nitrogen, creatine, thyroxine I¹³¹ disappearance, and sodium. These results indicate that both thyroxine and heat significantly alter several blood constituents and these factors may aid in determining what mechanisms are essential for acclimation of lactating cattle to tropic and semi-tropic regions. The fact that there is an alteration in blood constituents due directly and indirectly to a significant elevation of body temperature from effects of heat, indicates that the cow's thermogenesis may be controlled by some of the hormones and enzymes which remarkably maintain blood constancy.

¹ Contribution from the Missouri Agricultural Experiment Station Journal Series no. 2874. Approved by the Director.