Ovulatory follicle size investigated by ultrasonography and single artificial insemination with ovulation induction in the Japanese macaque (Macaca fuscata)

In the Japanese macaque, artificial insemination (AI) has been successful, but it required repeated AI two to three times a day under anesthesia until ovulation was confirmed by laparoscopy. To reduce this invasiveness, the ovulation timing and size of preovulatory follicle need to be elucidated. However, ovulatory follicle size is not well understood as monitoring ovarian dynamics using ultrasonography has never been performed in this species. Further, although ovulation induction facilitates establishing the AI protocol, the effect of gonadotropin releasing hormone (GnRH) on ovulation induction has not been studied. Monitoring of ovarian dynamics by ultrasonography of six spontaneous ovulations clarified that the diameter of the ovulatory follicle before ovulation was 7.4 +/- 1.5 (5.1-9.6 mm) and that ovulation occurred from Day 12 to 14 of the menstrual cycle. The effect of GnRH on ovulation induction was monitored in three monkeys, and one day after GnRH administration ovulations were induced with follicles of diameter of 4.7-7.4 mm. Further, AI with ovulation induction by GnRH was performed seven times using four females. Semen were inseminated in the uterus in four cases and into the cervix in three between Day 8 to 14 of the menstrual cycle. Only one female inseminated in the uterus on Day 12 became pregnant, but fetal development stopped at around 50 days of gestation. The present study investigated a less invasive single AI protocol with ovulation induction in the Japanese macaque, and the insemination technique needs to be developed further to improve the pregnancy rate.