Abstract :
The purpose of the study was to investigate the effects of different doses of equine chorionic
gonadotropin (eCG) treatment on follicular development, ovulation and pregnancy rate
during the breeding season in fat-tailed Chall ewes. Seventy-two cycling (62.5 ± 2.5 kg),
multiparous Iranian Chall ewes were used in the trial. The ewes were randomly allocated
to 6 groups (n = 12/group). Estrus was synchronized with the aid of controlled intravaginal
drug release (CIDR) devices, inserted for 14 days. At the time of CIDR removal (day 14),
the ewes received i.m. either 0 (control group, G0), 450 (G450), 550 (G550), 650 (G650),
750 (G750) or 850 (G850) IU eCG. Vasectomized rams were used to detect estrus in the
ewes from 24 h after CIDR removal. Ovarian follicular activity was monitored with the aid
of transrectal ultrasonography on the day of CIDR insertion (day 0) and daily from the
day of eCG treatment (day 14), until estrus (day 16). During these days, blood samples
were collected for the determination of plasma progesterone and estradiol concentrations.
Laparoscopic intrauterine inseminations were conducted 54–60 h after CIDR removal. The
number of CL’s and pregnancy diagnosis was recorded using ultrasonography 7 and 54
days following AI, respectively. Half of ewes in control group and most of the ewes treated
with eCG showed signs of estrus within 36 h of CIDR removal. The ewes in groups G750
and G850 recorded the highest number of large follicles at estrus and CL’s 7 days later. The
pregnancy rate in groups G550 (75.0%) and G650 (75.0%) was higher (P < 0.05) than that in
the other groups. The ovarian response and estradiol concentration, as well as pregnancy
rate showed that 550 or 650 IU eCG treatment is the most effective doses in improving the
pregnancy rate in Iranian Chall ewes.
