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Ruminant Nutrition and Forage Utilization
Asian-Australasian Journal of Animal Sciences 1991;4(3): 293-298.
DOI: https://doi.org/10.5713/ajas.1991.293    Published online September 1, 1991.
Effect of environmental temperature and feed intake on plasma concentration of thyroid hormones in dairy heifers
B. P. Purwanto, M. Fujita, M. Nishbori, S. Yamamoto
A study was conducted to determine the effect of environmental temperature and level of food intake on plasma concentration of thyroid hormones. Three dairy heifer were used in an experiment which consisted of three level of chamber temperature (10, 20 and 30째C) and three levels of food intake (100, 75 and 50% of recommended requirements). The analysis showed significant effects of environmental temperature on plasma triiodothyronine concentration, rectal temperature, respiration rate and heart rate but not on heat production. The range of plasma triiodothyronine was 2.51~1.79 ng/ml when the environmental temperature varied from 10 to 30째C. Effects of feed intake level were significant for heart rate and heat production. Heat production decreased from 25.9 to 20.0 kJ/kg0.75 h when the TDN intake decreased from 66.3 to 35.1 g/kg0.75 d. There was no interactive effect of environmental temperature and feed intake level. Plasma triiodothyronine concentration decreased under high environmental temperature without any changes in heat production. The effect of environmental temperature and feed intake level on the physiological function of thyroid gland, as indicated by the relative circulating rate of thyroid hormones, were found to be clear.
Keywords: Environmental Temperature; Feed Intake; Circulating Rate of Thyroid Hormones; Heat Production; Dairy Heifer

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