MORPHOLOGICAL AND FUNCTIONAL-CHARACTERISTICS OF PREOVULATORY FOLLICLES IN LARGE WHITE AND MEISHAN GILTS

Research was conducted to determine whether there are preovulatory follicular characteristics unique to Chinese Meishan (MS) sows that may contribute to their high prolificacy compared to that of European breeds. Follicles were recovered during the late follicular phase, following altrenogest withdrawal, from the ovaries of MS and Large White (LW) gilts before and after the administration of hCG given to mimic the LH surge. Following incubation of whole follicles for 1 h in vitro, media were collected for measurement of estradiol-17 beta, testosterone, and progesterone concentrations, and follicles were either fixed to assess number of granulosa and theca interna cells or cut into explants to test for aromatase activity over an additional 24-h incubation period. In MS gilts, follicles were smaller before and after hCG, although their growth was greater after hCG than was the growth of LW follicles. The LW and MS follicles contained relatively similar numbers of theca interna cells; whereas the numbers of granulosa cells in MS follicles were marginally (before hCG) or significantly (after hCG) less than those found in LW follicles. Before hCG, follicles of comparable size from both breeds produced similar amounts of estradiol and progesterone, whereas MS follicles produced less (P < .05) testosterone. Aromatase activity was not stimulated by FSH in either case, although a breed x follicle size interaction (P < .05) indicated a different pattern of aromatase activity between the breeds. After hCG, testosterone production was similar in MS and LW follicles, but estradiol (P < .05) and progesterone (P < .01) production were greater in MS follicles. Regardless of the timing relative to hCG and criteria used (size, steroid), heterogeneity of the ovulatory cohort was similar between MS and LW ovaries. In conclusion, MS and LW follicles differ in mechanisms controlling granulosa cell division, steroidogenesis, and luteinization.