Induction of follicular growth in the squirrel monkey (Saimiri sciureus): enhanced recovery of mature ova for fertilization in vitro.

In order to improve the rate of recovery of mature ova over those previously reported, we evaluated a new hormonal regimen for induction of follicular growth in the squirrel monkey. This regimen, which consisted of 50 IU pregnant mare's serum (PMS) per day for 4 days followed by 50 IU PMS and 250 IU human chorionic gonadotropin (hCG) on the 5th day, gave an average yield of 2.3 mature ova per animal from 14 experiments involving 11 animals. Ova were recovered through laparotomy or laparoscopy 18 h after PMS and hCG. This number reached 3.3 per animal when ova matured in vitro were included. The fertilization rate was significantly higher for ova matured in vivo (44%) than for in vitro-matured ova (7%) (P less than 0.05), showing the importance of recovering mature ova for successful fertilization in vitro. In agreement with previous observations, a seasonal pattern was noted for the response of animals to induction of follicular development, with a reduction in response occurring during a summer period from July to September. Our observations also suggest the occurrence of immunologic problems associated with the use of PMS in the squirrel monkey.