Hormonal changes during forced moult induced by progesterone in domestic hen.

Forced moulting has been induced in domestic hens by progesterone treatment (5 mg/day) for 25 days. Moult happened between the 11th and 19th day after the first treatment. Endocrine changes were followed during the moult by blood sampling in one week intervals. At the time of the last sampling, new egg laying cycle was initiated in all birds. Plasma progesterone concentration increased significantly in response to the treatment then tended to decrease. Oestrone and testosterone levels were the lowest during the period when feather loss was most intensive and increased in the course of feathering. This increase was significant in the case of oestrone. The level of 17-beta-oestradiol did not vary during moult induced by progesterone treatment. Plasma concentration of thyroxine significantly increased during feather loss, showing a maximum in the second and/or third week after the beginning of the treatment, while it decreased when feather growth had begun. Plasma triiodothyronine as well as corticosterone levels were the highest during the latest phase of moult, at the time of feather outgrowing. It has been supposed that moulting would be initiated in response to the synergistic effect on feather follicles of progesterone and thyroxine, which was stimulated by the progesterone treatment. The atrophic stage of the ovary suggested that progesterone was probably of adrenal origin. It was assumed that triiodothyronine and oestrone were responsible for controlling feather outgrowth.