Effect of Short-Term Fasting on Thyroid Activity of Cattle at Various Environmental Temperatures

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Abstract
Six nonlactating Holstein cows were fasted and subjected to different environmental temperatures. The effect of fasting for 8 and 24 hr. on thyroxine I131 disappearance rate and the plasma PBI was recorded. The thyroxine I131 disappearance rate increased significantly after 8 hr. of fasting, but after 24 hr. of fasting it was similar to that of the fed animals. The plasma PBI was not affected by fasting. The data indicated an inverse relationship between the thyroid activity and environmental temperature in fasting cows. The increase in thyroid activity in fasting animals at 1° C. compared with 18° C. suggests that thyroid function is dependent mainly on environmental temperature and not on feed intake. Raising the environmental temperature above 18° C. caused a depression in thyroid activity. It is also suggested that increasing the period of fasting for several days may result in a depression in thyroid activity. The possible mechanisms involved in thyroid changes under fasting are discussed, and a convenient laboratory method for fasting the bovine has been described. Copyright © 1966. American Society of Animal Science . Copyright 1966 by American Society of Animal Science