XXV.—An Experimental Analysis of the Plumage of the Brown Leghorn Fowl

Abstract

General Summary1. The plumage of the Brown Leghorn fowl is analysed and the extent of its dependence on the activity of the thyroid and gonad is discussed.2. Hypothyroidism results (a) in a diminution in the amount of melanin and a coincident increase in the red pigment; (b) in an increase in the amount of fringing due to a lack of barbule formation. The female pattern tends to disappear.3. Hyperthyroidism in the male gives exactly the opposite effect—i.e. the melanin increases in amount while the red pigment and fringing tend to disappear. In the female the effect of hyperthyroidism is slight, and with moderate doses of thyroid there is practically no modification of the female pattern of pencilling and no melanin appears in the breast. The neck hackle, however, becomes darker and shows a decrease in fringing.4. From these results, together with what is known concerning the effect of gonad on plumage, a hypothesis is advanced, that whereas the plumage typical of the male is developed independently of the gonad and depends for its maintenance on a certain level of thyroid functioning, both gonad and thyroid play a part in regard to that of the female; the former stimulates the latter to a higher level of activity than that present in the male and so indirectly causes a hyperthyroid effect on the feathers. At the same time it modifies this condition by acting directly on the feathers and restricting the deposition of melanin.5. The fact that in both sexes the plumage in the young chick is similar to that of the female puts this theory in question. There is evidence to show, however, that yolk may have a modifying effect on plumage similar to that of the ovary, and thus the doubt regarding the validity of the hypothesis can be removed by the suggestion that the chick plumage develops under the influence of the yolk in its own yolk sac. This second theory gains confirmation by a study of the atypical plumage which is occasionally met with in growing females, and also by a consideration of the type of plumage developed in juvenile females following the successful implantation of testis.

Biological methods of diagnosing equine pregnancy II—The capon test

“…They found that the resemblance to female feathers was much more striking in respect of shape and structure, but as related to colour there was an evident action towards the reduction of red pigment, varying in degree in different birds but tending to be arranged in " stippling " when present. These experiments were repeated on our own stock, but while our results agreed with the former in respect of changes of structure in the feathers from male to female type, it was not possible to confirm the opinion of Cole and Reid that the changes in patterning were suggestive of the pigment distribution found in the normal female (Greenwood and Blyth (1929)). Further, in the breast-a region which the previous authors did not discuss-there were never any indication of a tendency for the black to be replaced by the female colouration (red).…”

“…It has been shown by various workers (Goodale (1916);Finlay (1925);and Greenwood and Blyth (1929)) that while the plumage of the normal female of this breed depends for the maintenance of its characteristic pattern and colour on the presence of ovary (secreting ovarian hormone), the plumage in the male is not significantly affected by the presence or absence of testis and is, in fact, of the neutral or asexual type exhibited by the completely gonadless bird of either sex. (The assumption of typical female plumage ensues as a result of the successful implantation of ovary into such individuals.…”

“…Experiments in which thyroid gland was removed showed that the operation resulted (1) in a diminution in the amount of melanin and a coincident increase in the amount of red pigment; (2) in an increase in the amount of fringing due to the lack of barbule formation (Greenwood and Blyth (1929)). Hyperthyroidism in the male gives exactly opposite effect.…”

Variation in plumage response of brown leghorn capons to oestrone II—intradermal injection

“…It may be considered that the action of oestrone is to inhibit the deposi tion of melanin in the feathers (Greenwood and Blyth, 1929); this action is practically complete in the breast region of the female but incomplete in other parts of the body such as the back and saddle where the melanin is restricted to fine broken lines resulting in a characteristic pencilled pattern. In females in which the black pigmentation is not entirely absent from the breast it is found to be concentrated mainly in the lateral feathers: faint stippled patterns occur, becoming more marked towards the outer edge of the tract, and always heavier on the outer (right) side of the feather, i.e., on the opposite side from that on which the half bar of red pigment was found in the experimental feathers.…”

A study of the genetic control of black-red pigment patterns in the fowl

“…...the period for feather growth was shortened sig nificantly in the thyroid fed birds.... Greenwood and Blyth (1929) found feather growth slower in completely thyroidectomized birds. Chu (1938, p. 555) speaking of the period of time necessary for feather growth reported it "...lengthened in the thyroidectomized group.…”