SUPEROVULATION CAN REDUCE THE DEVELOPMENTAL COMPETENCE OF BOVINE EMBRYOS

This study was done to determine if different superovulatory regimens could have an effect on the percentage of embryos produced using IVM/I VF/IVC. Cyclic heifers (n=22) were superovulated between Days 8 and 12 of the estrous cycle with 4, 6 or 8 constant doses of FSH-P (4 mg eac h, twice daily) +/- the addition of 1 mg prostaglandin 24 h before sla ughter. Ovaries from these superovulated cows and from untreated cows were collected and the follicles dissected. Oocytes were classified ac cording to the appearance of their cumulus and cytoplasm. Individual c ulture as well as group culture were performed but an individual cultu re reduced the percentage of oocytes developing into embryos for both untreated and superovulated animals. The results indicated that despit e the superovulation regimen the developmental competence of the oocyt es collected was lower (0 to 15% embryos) than that of oocytes from un treated animals (20 to 34% embryos). Small follicles (less than or equ al to 2.7 mm) yielded mostly oocytes with an incomplete or partially e xpanded cumulus investment that never developed into an embryo. Differ ences in the morphology of the oocytes from medium (2.7 to 8 mm) and l arge (greater than or equal to 8 mm) follicles were apparent, but equa l developmental rates were obtained between all classes of oocytes (12 and 8% embryos, respectively). Follicular atresia was reduced signifi cantly after superovulation (81% nonatretic follicles in treated vs 42 % nonatretic follicles in untreated animals); however oocytes from atr etic and slightly atretic follicles developed similarly to those from nonatretic follicles. These results suggest that although superovulati on increases follicular size and decreases atresia, these conditions a re not sufficient to confer developmental competence on the oocytes.