Hen feathering

Lore & Background

Hen-feathering in cocks is controlled by a simple autosomal dominant gene, designated Hf by F. B. Hutt in 1958. Both homozygous Hf/Hf and heterozygous Hf/hf males exhibit hen-feathering, while hf/hf males have normal feathering. Female carriers of the Hf gene cannot be identified without progeny tests. Attempts to demonstrate genetic linkage to several known loci have been unsuccessful.

Reader's Guide

Hen-feathering is significant because it illustrates a sex-limited genetic trait with a clear hormonal mechanism. The condition requires masculine hormones for expression; feathers develop under the influence of testosterone, but the trait results from enhanced aromatase activity in the skin, converting androgens to estrogens. This increased estrogen formation in skin and peripheral tissues leads to female-type plumage in males. The average rate of aromatase activity in heterozygous Hf/hf chicks is about half that of homozygous Hf/Hf chicks, yet half-maximal enzyme levels suffice for full female feathering. The condition shows variable expressiveness: heterozygous males may display only a few female feathers in their first adult plumage but achieve complete female plumage after the first moult. Some old males may revert to normal male plumage due to subnormal testicular activity. The condition has been compared to aromatase excess syndrome in humans, which causes gynecomastia in boys and precocious puberty in girls, and is also inherited in an autosomal dominant fashion.

Did You Know?

• The genetic symbol Hf for hen-feathering was proposed by F. B. Hutt in 1958.
• Heterozygous Hf/hf males may show only a few female feathers in their first adult plumage but develop complete female plumage after the first moult.
• Enhanced aromatase activity in the skin of chickens carrying Hf leads to increased estrogen formation, which can be several hundred-fold higher than in normal birds.