Hypophysectomy of birds IV-Plumage changes in hypophysectomized fowls

We have previously described the effects of hypophysectomy on the reproductive organs and comb of the fowl. It remains to consider the plumage changes. Castration of the normal male fowl causes no plumage changes except slight lengthening of the feathers. Ovariectomy of the hen, however, results in reversal of the plumage to the male type. The plumage of the normal male is thus of the asexual or neutral type found in the gonadectomized bird of either sex (Goodale, 1916; Pézard, 1918). We expected, therefore, to find little change in the plumage of the hypophysectomized cock, in spite of the virtual destruction of the testis (Hill and Parkes, 1934), but a definite reversal of the hen’s plumage to the male type. The changes observed were actually very different; Brown Leghorn cocks have shown remarkable plumage changes, the hens much less obvious ones. We are convinced that the chief factor concerned in these plumage changes is thyroid deficiency. It is well known that there is an intimate relation between hyper- and hypo-thyroidism and plumage type (see Greenwood and Blyth, 1929). Thyroidectomy causes inability to produce the black pigmentation on certain areas of the body, especially in such breeds as the Brown Leghorn, and increases the fringing of the feathers due to lack of barbules. Changes such as these are the most obvious feature in the hypophysectomized fowl, and since we have demonstrated that they can be corrected by the administration of thyroxine, there seems little doubt that the thyroid atrophy which is known to follow hypophysectomy in mammals also occurs in birds and that this is the decisive factor in the post-hypophy-sectomy plumage changes. The study of plumage has now become a specialized branch of developmental physiology, largely owing to the researches of the Chicago workers in America, of Zawadowsky in Moscow, and of Greenwood in this country (see Lillie, 1932; Lillie and Juhn, 1932; Zawadovsky, 1927; and Greenwood and Blyth, 1929, for comprehensive papers with references). In the circumstances we have hesitated to attempt any complete analysis of the effects of hypophysectomy on plumage; such an analysis will clearly demand detailed knowledge of the subject. Our aim in giving the present description is to indicate the general nature of the changes, in the hope that they will be fully dealt with by other workers.