Previously we have demonstrated that the oocyte embryogenic competence of prepubertal heifers is animal age dependent and that gonadotropin treatment of animals improves the oocyte competence (Presicce et al, Biol. Reprod 56:386-392, 1997). The objective of the present study is to investigate the animal age and hormonal dependence of oocyte competence in pigs. Three groups of pigs (6 animals per group) of different ages (2 mo., 4 mo., 6 mo.) were i.m. injected with 500 iu, 1000 iu, or 1500 iu of PMSG 48 h prior to the removal of ovaries, respectively. Oocytes collected from two different size follicles (<2 mm and 
2 mm in diameter) were compared for their developmental competence. Oocytes from 7-months-old postpubertal pigs (no PMSG stimulation) were also tested as retrospective controls. Oocytes were matured in NCSU23 medium containing 10% porcine follicular fluid, 0.1 mg/ml cysteine, and 10 ng/ml EGF with hormonal supplementation (10 IU/ml hCG, 10 IU/ml PMSG) for 20-21 h and without hormones for an additional 20-21 h. Oocytes were then fertilized with frozen-thawed boar semen and cultured for 7 days. Blastocyst development increased with animal age (0%, 8%, 13%, 27% for 2 mo., 4 mo., 6 mo., 7 mo. in control groups, respectively, and 0%, 4%, 15% for 2 mo., 4 mo., 6 mo. in PMSG groups, respectively). However, hormonal treatment did not significantly affect the blastocyst rate over the non-stimulated group at any given age. Oocytes isolated from the larger follicles had a higher cleavage (84% vs. 74%, p<0.05) and blastocyst rates (31% vs. 19%, p<0.05) than those from the smaller follicle in 7 months group. In conclusion, oocytes from pregnant pigs and oocytes from larger follicles were developmentally more competent over the younger prepubertal gilts. PMSG administration at the tested dosages did not seem to improve the oocyte competence.
This abstract is being presented on Monday, August 2 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.