DIFFERENTIAL SENSITIVITY OF OVARIAN FOLLICLES TO GONADOTROPIN STIMULATION IN BROILER AND LAYER LINES OF DOMESTIC-FOWL

Differences in the reproductive potential of female broiler parent and layer fowl are related to differences in the recruitment of follicles to the preovulatory hierarchy. Broiler and laying hens were fed ad li bitum or a restricted diet during rearing and ad libitum after sexual maturity. The sensitivity of thecal tissue, from ovarian follicles of different sizes, from layer and broiler fowl to stimulation by pregnan t mares' serum gonadotrophin (PMSG) was determined to test the hypothe sis that differences in egg production are associated with changes in the sensitivity of ovarian follicles to stimulation by gonadotrophin. The activity of ornithine decarboxylase 0.5-4 h after injection of 200 iu PMSG kg body mass was assessed in thecal tissue from small white f ollicles 2-3 and 5-6 mm in diameter and in the smallest preovulatory y ellow follicle. Basal activity was similar in layers and broiler breed ers. PMSG-stimulated ornithine decarboxylase activity in follicles of 5-6 mm diameter was greater in broiler breeders than in layers. There was no difference between the lines in PMSG-stimulated ornithine decar boxylase activity in follicles of 2-3 mm diameter or in small yellow f ollicles. It was concluded that the low egg production and high preval ence of eggs with defective shells in broiler parents compared with la yers may be related to the increased sensitivity of follicles to endog enous gonadotrophins at the critical stage of recruitment to the preov ulatory hierarchy.