Hen-feathered is having female plumage characteristics. In the Sebright and Campine breeds, the male chicken is hen-feathered, as exemplified by the male (left) and female (right) Silver Sebright bantam chickens shown below. The male has rounded feathers rather than the pointed feathers typical of males. A female chicken's plumage pattern is dependent on the presence of estrogen to feminize the feather follicle—that is, to direct the follicle to produce rounded feathers—in the hackles and tail. The Sebright and Campine breeds have a single gene mutation that results in the 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 Sebright and Campine chickens have a level of estrogen sufficient to feminize the growing feathers.
Male (left) and female (right) Silver-laced Sebright bantam chickens. Source: Jacquie Jacob, University of Kentucky