Temperature-humidity effects on thyroxin I¹³¹ disappearance rates in cattle

Abstract

A significant depression of the thyroxin I131 disappearance rate was observed in lactating Holstein cows at 80 F, 80% relative humidity (RH); 85 F, 50% RH; 85 F, 70% RH; 90 F, 40% RH; 90 F, 50% RH; and 95 F, 20% RH. Differences from values at 65 F were not significant at 80 F, 30% RH; 80 F, 50% RH; 90 F, 20% RH; and 90 F, 25% RH. At 85 F and 90 F temperatures the effect of high humidity in depressing thyroxin I131 disappearance rate was obvious. Depression of hormone and feed intake at the higher humid temperatures suggests that the depression of thyroid gland function may be related to alteration in hormonal utilization in the peripheral tissues or to a more direct temperature effect (probably neural) on both thyroid gland secretion and appetite center. Thyroxin I131 disappearance rates, feed intake and body temperatures are expressed graphically relative to a temperature humidity index (THI) (U. S. Weather Bureau). The data show some decline above a THI of 71 and a marked decline above 75. Submitted on January 26, 1962