This study was designed to determine the secretory patterns of gonadotropin releasing hormone (GnRH), luteinizing hormone (LH) and inhibin (IH) in serum and estradiol (E-2) and progesterone (P-4) in follicular fluids (FF) in cyclic gilts of the Erhualian (EH) and Large White (LW) pig breeds to explore the mechanisms regulating follicular development and prolificacy in Chinese Taihu pigs. Age-matched Erhualian (n = 5) and Large White (n = 4) gilts, 6.5-7.5 months of age, weighing 40-70 kg, were kept and fed under similar animal husbandry conditions. Blood samples were collected through indwelling jugular catheters. Follicular fluid was obtained at ovariectomy 30-36 h after onset of oestrus. GnRH, LH, IH, E-2 and P-4 were measured by radioimmunoassay. The serum GnRH concentrations in LW gilts were significantly higher (p < 0.05) than in EH pigs, while the mean LH levels were not significantly different between breeds. However, the peak LPI levels were significantly higher in EH than in LW gilts. The mean serum IH levels in EH were lower than in LW gilts (p < 0.01). Follicular fluid, IH and E-2 levels were positively correlated with follicle size and with higher IH and E-2 concentrations in the large follicles (diameter > 5 mm) compared to small follicles (diameter < 2 mm). Follicular fluid concentrations of these two hormones were higher in EH than in LW gilts. Follicular fluid Pq levels were not affected by follicle size or pig breed. It is concluded that (1) the breed of pig affects GnRH, LH and IH levels in serum, (2) the follicular IH and E-2 were positively correlated with the size of these follicles and (3) GnRH, LH, IH and E-2 could play a role in regulating follicular development and other processes of reproduction which might contribute to the high fertility of Taihu pigs.
