The total gonadotrophic activities of the anterior pituitary glands and blood plasma of hens, Gallus domesticus, during the moulting period were estimated using the assay method based on the weight increase of chick testis. The activities in both the pituitary and the blood of hens in the four groups classified according to the progress of moult were significantly higher than those of laying hens. Nevertheless, no detectable level of serum vitellin and a completely regressed ovary were found in moulting hens.
Anterior pituitary glands of moulting and laying hens were assayed for their fsh and lh activities by the use of the hcg augmentation method or the ovarian ascorbic acid depletion test. The fsh activity of the moulting hen was about twofold higher than that of the laying hen, whereas lh activity was about equal during the moulting and the laying periods.
The serum vitellin of moulting hens increased steeply with the injection of oestrogen over 3 days. When chicken anterior pituitary homogenate was injected once daily for 6 days to hens in the moulting period, a satisfactory follicular growth as in the laying hen was induced in all of the treated hens. Injection of pmsg into moulting hens for 6 days resulted in an increase of serum vitellin in all the hens and the formation of yellow follicles in 40% of the treated hens.
These results suggested that the failure of follicular growth in the moulting hen, despite high levels of total gonadotrophic activity in both pituitary and blood, might be due to an unbalanced secretion of endogenous gonadotrophins.