Feather Growth Rates in Thyroidectomized Hens Following Administration of Thyroxin. ∗

The feather growth rates of normal fowl have been shown to be modified by the administration of thyroid 1 , 3 as well as by estrogens, 4-6 Although a general retardation in feather regeneration has been noted in spontaneous 7 and experimental 8 , 9 hypothyroid conditions in fowl, no measurements were previously made on feather growth in the various body areas. Consequently we were interested in studying the effects of thyroid removal on feather growth in brown Leghorn hens and to see if thyroxin administration had the same effect on growth rates in athyroidic hens as follows its administration in normal individuals.

For the study of feather growth rates, 25 papillae in 5 rows of 5 papillae each were selected and marked in comparable areas in each bird for each of the regions measured. Measurements were made at 2- or 4-day intervals on posterior breast, anterior breast, back and saddle. All individuals studied were adults and beyond 6 months of age.

Regenerating feathers of adult thyroidectomized females, operated on or before 10 days of age, did not become measurable until 12 to 14 days after plucking as compared to 9 or 10 days in normals. During the period of rapid growth, the breast and back feathers grew more rapidly than the saddle, as seen in their growth rates and lengths on the 48th day (Table I). This is in marked contrast to the order of growth rates in normal hens where posterior breast and saddle feathers grow more rapidly than back and anterior breast. Feather growth continued for a longer period in thyroidectomized hens than in normals. Breast and back feathers revealed a lesser reduction in length and growth rate than the saddle.