Feathers as Indicators of Concentration of Female Hormone in the Blood. ∗

Abstract

In the first observations made in this laboratory on the induction of feathering in capons and cocks subsequent to injections of chemically prepared hormone during the period of feather regeneration, regional variations in the degree of plumage responses became evident. It was noted that feathers having a more rapid growth rate required definitely higher concentrations of hormone for the female reaction than feathers having a slower growth rate. 1 The growth rates of feathers in various parts of the body have now been accurately measured, and constant regional differences have been established. The birds used for these experiments were brown leghorn fowls, and in this breed the capon is similar in plumage to the cock. In both cock and capon, the growth rate of the feathers is greater in the breast than in the saddle or back, and even greater in the posterior than in the anterior region of the breast. The ratio between the most rapidly and the most slowly growing feathers when measured in growth in length per day is approximately 2:1. In the hen differences in growth rate in various parts of the body are slight, and the general rate for all is intermediate between the maximum and minimum rates of the cock. The threshold concentrations of hormone required for the reaction are closely correlated with this observed difference in growth rate.

Feathers formed on a capon receiving regular effective daily injections of female hormone are completely female in character; if, however, the injections are restricted to short periods of time, then bars or patches of female color are laid down on an otherwise male type of feather. One single injection will, if sufficiently large to produce the threshold concentration, be recorded by the feather.