FOLLICLE DYNAMICS AND AROMATASE-ACTIVITY IN HIGH-OVULATING MEISHAN SOWS AND IN LARGE-WHITE HYBRID CONTEMPORARIES

This study compared the dynamics of follicle development during the fo llicular phase in Meishan sows (n = 10) with a high ovulation rate, wi th those in contemporary Large-White hybrid sows (n = 12) (ovulation r ates: 27.7 and 17.6, respectively; p < 0.01). Ovaries were recovered o n Day 16 or 19 of the cycle, and all follicles greater than or equal t o 1 mm in diameter were dissected. Fluid was aspirated from all those greater than or equal to 2 mm, and the granulosa and theca cells were incubated to estimate aromatase activity and estradiol production. The total number of follicles dissected was higher in Meishan than in Lar ge-White hybrid animals (p < 0.001), and whereas the number decreased (p < 0.01) between Days 16 and 19 in Large-White hybrid sows, there wa s no significant change in Meishan animals. The mean diameter of Meish an follicles recovered on each of Days 16 and 19 was smaller (p < 0.00 1) than that of those recovered from Large-White hybrids. Total estrad iol production in vitro was higher (p < 0.01) by follicles greater tha n or equal to 2 mm from Meishan sows. There was an interaction (p < 0. 01) between day of the cycle, breed, and follicle diameter in aromatas e activity in both granulosa cells and theca tissue, and in follicular fluid estradiol concentrations in follicles greater than or equal to 2- < 6 mm. The largest three size categories of follicles recovered on Day 19 from each breed were classified as preovulatory (29.0 and 17.7 for Meishan and Large-White hybrid, respectively), and the mean diame ter was smaller (p < 0.001) in Meishan animals. Follicular fluid estra diol concentrations and total estradiol synthesis by granulosa and the ca combined were higher (p < 0.05) in Meishan than in Large-White hybr id sows. In conclusion, high-ovulating Meishans maintained a higher nu mber of follicles during the follicular phase, which overall synthesiz ed more estradiol in vitro, than did Large-White hybrid animals.