Abstract :
Due to the substantial contribution of lambing rate to profitability of sheep holders, the
present trial was investigated the effects of eCG injection combined with FSH and GnRH
administrations on ovarian follicular development and the lambing rate in Afshari ewes
during breeding season. The estrous cycle of 64 cycling multiparous Iranian Afshari ewes,
weighing 65
±
2.5 kg, was synchronized using CIDR’s, inserted for 14 days. eCG (300 IU) was
injected to ewes a day before CIDR removal. The ewes were allocated randomly to 1 of 4
groups (n = 16/group). Control group did not receive FSH treatment. In FSH/0h, FSH/12h and
FSH/24h groups, ewes received 10 mg FSH at CIDR removal, 12 or 24 h later, respectively.
GnRH (50 g) was administered 48 h following CIDR removal to half of each group of ewes.
Ewes were mated with the proven rams. Ovarian follicular activity was monitored by transrectal
ultrasonography at CIDR removal (day 0) and a day later (day 1). The repeated data
analyzed using the mixed procedure of SAS (9.1). Effects of weight and age of ewes were
added as a covariate to the model. The reproductive parameters (%) were analyzed using
the chi-square test. The results have been showed that FSH treatment did not increase the
mean number of small and medium sized follicles. Following FSH treatment, the mean number
of large follicles had a tendency to increase (P < 0.1) in FSH/12h group of ewes. Lambing
rate in control, FSH/0h, FSH/12h and FSH/24h were 137.50%, 131.25%, 150.00% and 181.25%,
respectively. The lambing rate and litter size increased to
≥150% (P < 0.05) in groups of ewes
which received GnRH. FSH/24h group of ewes had a significantly higher lambing rate, litter
size and multiple birth rate (P < 0.05) compared to other treatment groups. In conclusion,
GnRH injection 48 h after CIDR removal and eCG injection increase the lambing rate, litter
size and multiple birth rates in ewes. The lambing rate (>180%) was greater in ewes which
eCG injection was combined with FSH treatment 24 h after CIDR removal with or without
GnRH injection. These results indicate that lambing rate and litter size after CIDR and eCG
treatment can be increased when GnRH is administered 48 h after CIDR removal or when
FSH is given 24 h after CIDR removal.
