Assessment of oocytes retrieved from stimulated and unstimulated ovaries of pig-tailed macaques (Macaca nemestrina) as a model to enhance the genetic diversity of captive lion-tailed macaques (Macaca silenus)

Abstract

Steroid hormone levels were measured during unstimulated menstrual cycles of pig-tailed macaques (Macaca nemestrina) and lion-tailed macaques (Macaca silenus). The values were similar, suggesting that the pig-tailed macaque may be an appropriate model for in vitro fertilization and embryo transfer in the lion-tailed macaque. Two follicular stimulation protocols were compared to evaluate the yield and quality of the oocytes obtained from pig-tailed macaques. Five animals received a regimen of PMSG (Protocol I) and five received a regimen of Pergonal (Protocol II). Oocytes from natural cycles were obtained from seven pig-tailed macaques during 21 cycles. If the oocytes extruded a polar body, they were inseminated and then observed for penetration and cleavage. Oocytes that produced quality embryos were transferred to recipient pig-tailed macaques or rhesus macaques (Macaca mulatta). Oocytes from natural cycles had a higher percentage of good embryos produced from inseminated eggs (22.7%) compared to Protocol I (10.3%) or Protocol II (14.2%). However, Protocol I and Protocol II yielded more quality embryos/cycle (2.0, 1.4, respectively) than natural cycles (0.24). Pig-tailed macaques were refractory to a second PMSG protocol, but Pergonal and natural cycles could be repeated on the same individual before or after PMSG. A total of 12 embryos were transferred to six pig-tailed macaques and three rhesus macaques during natural or stimulated cycles. No pregnancies resulted. Refinement of IVF-ET techniques in pig-tailed macaques should make the procedure a viable choice to enhance the genetic diversity of captive lion-tailed macaques.