Abstract
The influence of the difference in the method used for the estimation of thyroid function on the evaluation of the genetical difference among various breeds of chickens was studied. The methods used were (1) uptake of 131I of HIMENO et al. (1961), (2) 131I-release rate of OHNISHI et al. (1960), (3) thyroxine secretion rate of TANABE and KOMIYAMA (1960) (T.S.R.-I), (4) thyroxine secretion rate of MELLEN and WENTWORTH (1960) (T.S.R.-II), and (5) plasma thyroxine levels of ISHII et al. (1970, 1971). The chickens used were 7-week-old males of (1) Fayoumi, (2) White Plymouth Rock (WR-A), (3) White Leghorn possessing dw (dwarf) gene (WL-F-dw), (4) White Leghorn possessing DW gene (WL-F-DW), and (5) Silky breeds Another line of White Leghorn breed (WL-II) was also used for the measurement of plasma thyroxine levels.The uptake of 131I by the thyroid gland was greater in the following order. Fayoumi, WL-F-dw, WL-F-DW, WR-A, and Silky which was the greatest, although the difference between WL-F-dw and WL-F-DW was statistically not significant. The order of 131I-release rate was reciprocal to the order of the uptake. In the T.S.R.-I, the order was the same as in the uptake, While in S.R.-II the order was the same in the release rate. The plasma thyroxine level was the highest in WL-II, and lower in the following order. Fayoumi, Silky, WL-F-DW, WL-F-dw, and WR-A which was the lowest.
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