SUPEROVULATORY RESPONSE IN ANESTROUS EWES IS AFFECTED BY THE PRESENCEOF A LARGE FOLLICLE

Superovulatory response to conventional treatment with eCG (1200 IU) a nd progestagen sponges (MAP, n=9; FGA, n=9; or controls without sponge , n=6) was studied in Corriedale anestrous ewes. The follicular popula tion just before the administration of eCG and the total ovarian respo nse (large anovulatory follicles plus normal CL and prematurly regress ing CL) to treatment were determined after laparotomy. Pretreatment wi th progestagen did not modify the number or class of follicles greater than 1 mm observed on the ovarian surface at the time of eCG administ ration (19 +/- 2.2 follicles vs 19 +/- 2.9 follicles, for pooled proge stagen-treated groups and control groups, respectively; mean +/- SEM) but significantly decreased the number of large anovulatory follicles (4.7 +/- 1.0 vs 10.2 +/- 2.6; P less than or equal to 0.01) observed f ollowing treatment. Progestagen-treated animals were classified accord ing to the presence (n=13) or absence (n=5) of a large follicle (LF: g reater than or equal to 4 mm diameter) on the ovarian surface at the t ime of eCG treatment; a qualitatively better superovulatory response w as observed in ewes without large follicle (large anovulatory follicle s: 1.6 +/- 0.7 vs 5.8 +/- 1.3, P less than or equal to 0.05; normal CL : 7.0 +/- 1.4 vs 3.8 +/- 1.0, P less than or equal to 0.1; normal CL/t otal ovarian response: 78.7 +/- 10.1% vs 34.9 +/- 8.2%, P less than or equal to 0.01; for ewes without LF and ewes with 1 to 2 LF respective ly). No differences were observed in the individual ovulatory response when comparing ovaries ipsilateral or contralateral to LF in a same a nimal, indicating that the effect of LF on the superovulatory response would be fundamentally systemic. This work shows that, similar to wha t occurs in cows, the presence of a large follicle at the time of gona dotropin administration decreases the superovulatory response in anest rous ewes.