The effects of insulin-like growth factor I (IGF-I), alone, and in combination with LH or transforming growth factor α (TGF-α), on replication and progesterone production by cultured avian granulosa cells obtained from the three largest (F1–F3) follicles were studied. IGF-I and TGF-α stimulated proliferation of granulosa cells in a dose-dependent manner, and responsiveness decreased as the cells matured. IGF-I stimulated progesterone production from granulosa cells of all the follicles with no change in ED₅₀ value during follicular maturation; however, the maximum response was from cells derived from F1 follicles. IGF-I plus LH had an additive effect on progesterone production by cells from all follicles. In contrast, TGF-α inhibited basal and LH- and IGF-I-stimulated progesterone production. These data show that IGF-I and TGF-α may interact with each other during granulosa cell maturation, such that efficacy of IGF-I increases, while that of TGF-α decreases before ovulation. Furthermore, both growth factors interact with LH, either to enhance or inhibit progesterone production by granulosa cells. However, LH, IGF-I and TGF-α combine to stimulate proliferation of granulosa cells.

The purpose of this study was to determine the presence of epidermal growth factor receptor and its potential ligands epidermal growth factor (EGF) and transforming growth factor α (TGF-α) in the tissues of the maturing follicles in the ovary of laying ISA-Brown hens using peptide-specific immunohistochemical methods. Cryostat sections, 6–8 μm thick, were made from fresh–frozen tissues of F1–F4 (largest to fourth largest) and large white follicles and they were immunostained for epidermal growth factor receptor, epidermal growth factor or transforming growth factor α using specific polyclonal antibodies. The EGF receptor and both ligands were detected in the granulosa, theca interna and theca externa layers of the follicles. The EGF receptor was localized both in the plasma membrane and cytoplasm of all cell types. EGF was predominantly cytosolic, whereas TGF-α was found in the plasma membranes and perinuclear areas of all cell types. The concentration of the receptor and both ligands decreased with follicular maturation. This observation is consistent with our previous observation that the response to EGF and TGF-α decreases as follicles mature, and thus provides further evidence that the receptor or the ligands may have a regulatory role in avian ovarian function.

Strain differences in reproductive performance were demonstrated between broiler breeder female chickens selected for growth (GL line) or for food conversion efficiency (FC line) and the improvement in reproductive performance due to feed restriction also differed significantly. Feed allowance effects on the maturation of ovarian follicles, the incidence of atresia and egg production differed between the two lines exposed to similar feeding protocols. Feed restriction reduced body weights significantly and to a similar extent in both GL and FC lines. The number of normal and atretic yellow follicles was significantly higher under ad libitum feeding and in GL line than it was in the FC line. In both lines, feed restriction decreased multiple ovulation and increased egg production. In culture, granulosa cells from the three largest follicles (F1, F2 and F3) increased progesterone production in response to LH, FSH and insulin-like growth factor I but responses were different between the GL and FC lines fed either ad libitum or restricted diets. Granulosa cells from the two or three largest follicles in GL and FC (ad libitum) lines produced similar amounts of progesterone in response to LH, FSH and insulin-like growth factor I whereas, in restricted birds, the progesterone production was of the rank order Fl > F2 > F3 in both lines. The responsiveness of the GL line fed ad libitum was higher for LH than for either FSH or insulin-like growth factor I but in the GL line fed a restricted diet, it was high for all the hormones. In the FC line, responses to LH, FSH or insulin-like growth factor I were high in ad libitum-fed birds, but low in birds fed a restricted diet for all hormones. Insulin-like growth factor I combined with LH or FSH significantly increased the progesterone production of granulosa cells from birds fed restricted diets of both lines and this effect increased with increasing follicular size. There was a lack of interaction between insulin-like growth factor I and LH or FSH in the regulation of progesterone production by birds of both lines fed ad libitum. Insulin-like growth factor alone or in combination with LH or FSH increased granulosa cell proliferation in birds fed ad libitum more than it did in birds fed restricted diets. The greater proliferation rate of granulosa cells of chickens fed ad libitum, in response to insulin-like growth factor I alone or in combination with gonadotrophins, leading to the simultaneous differentiation of two or three large follicles with high progesterone production in response to LH or insulin-like growth factor I, accelerates the rate of maturation of follicles. This may also be the major cause of erratic and multiple ovulations in broiler breeder female chickens fed ad libitum. In conclusion, insulin-like growth factor I, alone or in combination with LH or FSH, is an important component in the control mechanisms for follicular development in broiler breeder hens. It is this component that is targeted by feed allowance and inadvertently altered by selection for growth.