Effects of Heat-Alleviators on Endocrine Levels of Blood and Milk Yield of Dairy Cattle in Summer Hot Season

The endocrine levels of Co, T₄, T₃ in peripheral blood and the changes of T₄/T₃ ratio were tested by radio immunoassay after applications of heat-stress alleviators to dairy cattle. With the mean daily house temperature of 30. 7±1. 33℃ and the relative humidity of 75. 6±2. 50% in summer hot season. The results show that the Co levels in the test groups increased remarkably by 75. 3% with a significant difference (P<0. 01), and the levels of T₄, T₃ and T₄/T₃ ratios in the test groups increased by 13. 5% , 7.7% and 5. 5% respectively, with a significant difference (P> 0. 05) compared to the control group. The milk yield increased by 11. 0% with a significant difference (P<0. 01). The above results show that the changes of the endocrine levels should be identical with the increase in the milk yield.