Interrelations of Thyroid and Gonad in the Development of Plumage and Other Sex Characters in Brown Leghorn Roosters

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Abstract
The reproductive system of fowl thyroidectomized at 6-10 days of age remained juvenile in gross and histologic appearance as late as 2 yrs. of age. Their body wt. was approx. 1/2 of normal while the comb was 18-22% of normal size. Simultaneous injn. of thyroxin and androgens yielded a greater comb growth than follows admn. of either alone. Thyroidectomized roosters revealed a reduced spur growth and were observed not to crow or tread. All plumage stages exhibited a replacement of normal pigmentation by reddish-brown and a decrease in barbulation. Thus feathers became reddish-brown and lacy in appearance. Feather growth rates were reduced, but posterior breast had most rapid growth, as in normal. The [male] plumage pattern was produced with an adequate dose of thyroxin without regard to the level of androgen available. The [female] plumage pattern was not developed here with admn. of [alpha]-estradiol benzoate doses 20 X greater than is adequate for such an effect in normal fowl. Thyroxin appears to increase the utilization of gonadal hormones and may have a synergistic effect with them on the development of secondary sexual characters.