Follicular development and ovulation rate following different superovulatory treatments in Chall ewes

The purpose of the present study was to investigate the effects of three gonadotrophin treatments on follicular development and ovulation rate in Chall ewes. Thirty-three non-cycling, multiparous fat-tailed Iranian Chall ewes, weighing 62.5 ± 2.5 kg, were used in the trial. The ewes were allocated randomly to 1 of 3 groups (n = 11/group). Estrus was synchronized using CIDR's, inserted for 14 days with the following superovulation treatments being used: in group eCG/d14 the ewes received 1500 IU eCG on the day of CIDR removal (day 14); in group eCG/d12, 1500 IU eCG was administered 48 h prior to CIDR removal (day 12); in group eCG/d12 + FSH ewes were injected with 350 U eCG, 48 h prior to CIDR removal (day 12), followed by 12 ml FSH-P in six doses of 2.75, 2.75; 2.25, 2.25; 1, 1 ml over a 4 day period at 12 h intervals. Vasectomized rams were used to detect estrus in the ewes from 24 h after CIDR removal. Ovarian follicular activity was monitored daily with the aid of transrectal ultrasonograpy – from the day of superovulatory stimulation, until the day of estrus. Ewes in estrus were mated twice daily (morning and evening). The number of CLs was recorded using ultrasonography and laparoscopy, 7 days after mating. The number of large ovarian follicles at estrus was positively related to the number of small follicles at day 12 (P < 0.05, r = 0.56) in the eCG/d12 + FSH group of ewes. The number of large follicles at estrus and CLs 7 days later were higher in the eCG/d12 + FSH group, followed by the eCG/d14 group and the eCG/d12 group. It could be concluded that Chall ewes could be superovulated with eCG or with a combination of eCG and FSH. Of the three protocols tested, the eCG/d12 + FSH showed superiority in terms of the number of large follicles at estrus and CLs 7 days later.