Feed restriction in cyclic gilts: gonadotrophin-independent effects on follicular growth.

Our objective was to determine whether changes in metabolic hormones, induced by feed restriction, can alter follicle distribution in swine ovaries through effects independent of LH pulsatility. In a factorial arrangement, 24 gilts were fed a high or a low level of dietary energy (240 or 80% of maintenance requirements) and given an antagonist of GnRH or saline between days 3 and 12 of the oestrous cycle. Serial blood samples were collected on day 12 and ovaries on day 13. Antagonist treatment, that blocked LH pulsatility, decreased the number of follicles larger than 2 mm and increased the number of follicles smaller than 1 mm. The feed restriction did not alter gonadotrophin secretion, decreased the number of follicles smaller than 1 mm and increased the number of 1 - to 1.9-mm follicles. These findings indicate that feed restriction can alter the growth of small follicles independently of gonadotrophin levels.