Written by: Dr. Jacquie Jacob, University of Kentucky
Hen-feathering refers to the phenomenon of a male having female plumage characteristics—for example, the male has rounded feathers rather than the pointed feathers typical of males. (Refer to the article on the Anatomy of a Feather for more information about feather characteristics.) Examples of breeds that exhibit hen-feathering include the Sebright and Campine breeds.
Figure 1. Sebright chickens (male, left; female, right). Source: Jacquie Jacob, University of Kentucky
The development of secondary sexual characteristics as birds mature is a result of hormones produced in the testes and ovaries. The characteristics that develop depend on the balance between androgen and estrogen production. The female plumage type and pattern is dependent on the presence of estrogens to "feminize" the feather follicle, directing the formation of a more rounded feather in the hackles and tail. In breeds in which the feather color differs between males and females, the estrogens are responsible for the reduction in pigmentation in many of the feather tracts. The two breeds with hen-feathered males have a single gene mutation that results in excess production of the enzyme aromatase in several tissues, including feather follicles. Aromatase is the enzyme responsible for the conversion of androgens to estrogens. As a result, the feather follicles of male Sebrights and Campines have excess estrogen. The level of estrogen in the feather follicles is sufficient to feminize the growing feathers.
Androgens are hormones that control the development and maintenance of male characteristics. The most well-known androgen is testosterone. Androgens are required to induce growth of the comb and wattles in roosters. They are also responsible for roosters crowing. The growth of spurs, however, is independent of androgens and estrogen. Instead, spur growth is determined by the genetic sex of the bird.