Comparison of follicular heterogeneity and ovarian characteristics in Meishan and Large-White hybrid pigs

in Reproduction

Comparisons were made between characteristics of pre-ovulatory follicles recovered from prolific Chinese Meishan gilts (n = 12) and from European Large-White hybrid gilts (n = 13) in the late follicular phase preceding their fifth oestrous cycle, to determine whether there is an ovarian basis for the enhanced prolificacy in the Meishan. A total of 177 follicles per breed was classified as pre-ovulatory, based on follicular fluid oestradiol concentrations. Results obtained demonstrated high variability in all follicular characteristics in both breeds and no decrease in heterogeneity was evident in the Meishan. The Meishan follicles tended to be smaller (P < 0.06) and had less follicular fluid (P < 0.005), but total oestradiol content per follicle was similar (P > 0.1) with the result that the concentration of oestradiol in follicular fluid tended to be higher (P < 0.06) in Meishan than Large-White hybrid pigs. There were no differences between breeds in terms of testosterone concentration in follicular fluid, hCG binding to granulosa cells or total DNA content of granulosa cells. Concentrations of inhibin in follicular fluid were similar in both breeds (P > 0.1) which resulted in a trend towards less total inhibin content in Meishan than Large-White hybrid follicles (P = 0.065). Corpora lutea were recovered from both breeds (n = 12 per breed) on days 27–31 of pregnancy after mating at first, second and third oestrus:corpora lutea were smaller (P < 0.001) and contained less progesterone per corpus luteum in the Meishan (P < 0.05) than in Large White hybrid pigs. However, since ovulation rate was higher in these particular Meishan pigs (P < 0.005), total ovarian progesterone content per animal was similar in both breeds. These results demonstrate that there was no decrease in the variability in follicular characteristics from Meishan pigs. However, both follicles and corpora lutea were smaller in Meishan than in Large-White hybrid pigs, and progesterone per corpora lutea was also lower in the Meishan. In spite of their smaller size, Meishan follicular oestradiol content was similar to that of Large-White hybrid pigs, such that the oestradiol concentration in follicular fluid tended to be higher in Meishan follicles.

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