Spectrophotometric Identification of Feather Pigments in the Brown Leghorn Fowl

Abstract

BROWN Leghorn fowl show a strong sexual dimorphism in the plumage pigmentation, the female colouring being developed only in presence of the ovary whereas the male shades characterize intact or castrate bird alike. All feather tracts differ in some respects between the sexes ; the present discussion centres on the pectoral (breast) region which is salmon in the hen and black in the cock. In early studies of hormonal mechanisms in birds, Brown Leghorn cocks or capons with enforced feather regeneration were injected with an extract of human placentae, the preparation having been tested on the pullet oviduct for avian cestrogenic properties¹. With this procedure the treated males developed a salmon female breast feathering which was indistinguishable in colour from that of the corresponding area in the normal hen. In later experiments synthetic œstrogens were employed, and here, it appeared, a pigmentation was produced resembling, but clearly darker than, the usual female. This shade was variously thought a matter of dosage² ; a matter of dosage but transitory³ ; and as indicative of a genetic difference in the test fowl⁴. The last interpretation is not discounted, but it will be shown that two distinctly different modified breast feather pigments may follow from one single course of diethylstilboestrol treatment in one and the same Brown Leghorn capon. This is so because of the range of dosage requirements for feminization of the male breast feather tracts, the increase occurring in antero-posterior direction⁵. In favourable material, modified bars resembling the true female salmon were found in association with bars of a darker shade in feathers of more posterior location. This ‘darker’ shade, however, appeared more akin to the red which invades the breast tracts after thyroidectomy and which corresponds more closely with the red of the normal male saddle feather⁶. It seemed possible, therefore, that at certain levels the synthetic œstrogen produced effects comparable to thyroidectomy and that the darker pigmentation was in fact similar to if not identical with this male red. The foregoing inferences are now confirmed by Spectrophotometric differentiation of the normal female salmon from the normal red male and identification of each of these with modified breast feathers of the same capon following short-term œstrogen treatment.