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

Research was conducted to determine whether there are preovulatory fol licular characteristics unique to Chinese Meishan (MS) sows that may c ontribute to their high prolificacy compared to that of European breed s. Follicles were recovered during the late follicular phase, followin g 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, medi a were collected for measurement of estradiol-17 beta, testosterone, a nd progesterone concentrations, and follicles were either fixed to ass ess number of granulosa and theca interna cells or cut into explants t o test for aromatase activity over an additional 24-h incubation perio d. 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 thec a interna cells; whereas the numbers of granulosa cells in MS follicle s 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 progesteron e, whereas MS follicles produced less (P < .05) testosterone. Aromatas e 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 produc tion was similar in MS and LW follicles, but estradiol (P < .05) and p rogesterone (P < .01) production were greater in MS follicles. Regardl ess of the timing relative to hCG and criteria used (size, steroid), h eterogeneity of the ovulatory cohort was similar between MS and LW ova ries. In conclusion, MS and LW follicles differ in mechanisms controll ing granulosa cell division, steroidogenesis, and luteinization.