Thyroid Hormone Secretion Rates in Growing and Mature Goats

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Abstract
Dairy goats of four major breeds were used to determine the relationship between thyroid hormone secretion rate (TSR) and body weight. Goats ranged from 2 weeks to 6 years of age and 3 kg to 95 kg body weight. Twenty females were subjected to a total of 105 TSR determinations, while 14 males had 39 determinations. TSR was run every 3 months. TSR (mg/day) was related to body weight (kg) and the 3 primary measures used to calculate TSR (concentration in body pool, size of pool in liters, and rate of disposal of thyroxine from the body pool). Correlation coefficients were: thyroxine concentration and pool size, .038; thyroxine concentration and disposal rate, —.40; thyroxine concentration and TSR, .53; pool size and disposal rate, —.41; pool size and TSR, .72; and disposal rate and TSR, —.26. Age and TSR had a R2value of .35, while for body weight and TSR it was .53. When body weight and TSR were expressed as logarithms to comply with the mathematical expression Y = aXb, the R2 value was increased to .64. Pooling linear and quadratic effects of the logarithmic data resulted in R2 of .65, indicating no significant quadratic effect. A prediction equation developed for all 144 determinations was the following: Y (TSR, mg/day) = .010 × (body weight, kg).69. In other words, for every unit increase in body weight, there was a .69 unit increase in TSR. Prediction equation for 39 determinations on males was Y = .013 × .63 with R2 of .64, while it was Y = .010 X .70 for 105 tests in females with R2 of .63. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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