A history of six years' thiouracil treatment in a brown Leghorn hen.

Abstract

The history is recorded of a Brown Leghorn hen that received 0·5% thiouracil in the diet from 9 weeks of age until the bird was over 6 years old, when it was killed. During this period certain sections of the plumage exhibited a series of new and different pigments, while others remained relatively unchanged. The last category comprised the regions originally salmon; the feathers were structurally altered, but continued a duller shade of the original hue. Feathers of the dorsal tracts and the smaller wing coverts showed shades of orange and rust, resembling the modified male during the first 3 years. Thereafter, these feathers gradually became pale gold and small, but true female segments reappeared surrounding the shaft. Large wing and tail feathers were not greatly changed except the two most distal secondaries. At the end of the experimental period, proximally located, regenerating secondaries were laying down metallic black with some coarse brown mottling. Eggs continued to be laid, but intervals between clutches were greatly lengthened. Tests for fertility by artificial insemination were made at 3 and 6 years of age. Viable chicks were hatched at both times. Dissection of embryos and chicks in the second series showed greatly enlarged thyroids. Possible explanations of the appearance of black feather pigments in remiges and rectrices during such long-continued treatment with thiouracil are considered.