The Basal Energy and Nitrogen Metabolism of Dairy Calves in Hyperthyroidism Induced by Thyroprotein Administration

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Abstract
The extra energy and protein (nitrogen) expended in basal activities of the bovine induced by the feeding of iodinated casein have been studied by appropriate experiments on two Holstein bull calves. The basal metabolism of each calf, and the minimum endogenous urinary excretion of nitrogen, were studied when the calves were in the normal unstimulated condition, and also when they had come into equilibrium, as judged by pulse rate, respiration rate and rectal temperature, with a selected dose of iodinated casein (protamone). Under the conditions imposed, the basal metabolic rate of the calves was increased in hyperthyroidism by 31 and 35 percent, and the minimum endogenous urinary nitrogen by 19 and 16 percent, per m2 of body surface. The ratio of endogenous nitrogen to basal calories was lowered in hyperthyroidism from 2.56 mg. to 2.19 mg. with one calf, in which body weight was lost rapidly during protamone feeding, and from 2.14 to 1.93 mg. with the other. Thus, in experimental hyperthyroidism, both the basal expenditure of energy and the endogenous catabolism of nitrogen are elevated. An illustration is given of the practical significance of these results, indicating that the TDN cost of the extra milk produced in response to a practical dosage of iodinated casein may be increased by more than 100 percent over the normal cost, while the cost in terms of digestible crude protein may be increased over normal by about 50 percent.