Thyroid Secretion Rate in Swine1

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Abstract
A total of 257 daily thyroid secretion rate determinations were made on 213 animals representing the Poland China, Hampshire, Yorkshire and Duroc breeds by measuring the release rate of I131 from the thyroid gland of animals receiving daily injections of L-thyroxine. The mean daily thyroid secretion rate for all animals was found to be 0.39 mg. L-thyroxine per 100 lb. of body weight. The average secretion rate of 98 males (0.38 mg.) and 115 females (0.40 mg.) did not differ significantly. Significant breed differences were found with Poland China pigs having a higher secretion rate than Hampshire and Yorkshire pigs at low temperatures. However, the secretion rate of Yorkshire pigs was significantly higher than that of Hampshires and equal to that of Poland China pigs, when the average ambient temperature was above 36° F. Only a limited number of determinations were made on Duroc pigs. The average daily secretion rate of 24 animals 10 to 14 months of age was 0.19 mg., as compared to an average of 0.41 mg. of L-thyroxine per 100 lb. of body weight for 233 determinations made on pigs that were 2 to 8 months of age. This difference was significant. Significant within-sex and within-breed positive correlations were found between daily thyroid secretion rate and daily rate of gain of Poland China males and Yorkshire pigs. However, a significant association between thyroid activity and gaining ability was not observed in Poland China females or Hampshire pigs. Copyright © 1964. American Society of Animal Science . Copyright 1964 by American Society of Animal Science

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