Abstract It seems that; long exposure to equine chorionic gonadotropin (eCG) in ewe synchronization programs would stimulate the growth of ovarian follicles resulting in better reproductive performance. Therefore, the aim of present study was to expose Farahani ewes to longer duration of eCG by using an eCG-alhydrogel mixture as a slow-release eCG. Fifty Farahani ewes (3-4 years, 44 ± 1.3 kg BW, BCS 3.04±0.3 on scale 1 to 5) were treated with controlled internal drug release (CIDR) for 14 days. The experimental groups consisted of: control group receiving no eCG, and four groups of ewes receiving either 400 IU eCG or eCG-alhydrogel preparation (i.m.) at 24 h (-24S, and -24SR groups, respectively), or 48 h (-48S and -48SR groups, respectively) prior to CIDR removal. Blood samples were taken from two days before until one day after CIDR removal. Reproductive performance was recorded at lambing. There was no difference (P>0.05) between groups in terms of the pregnancy rate, lambing rate, fertility, multiple birth and fecundity. However orthogonal contrasts showed that the fecundity and multiple birth were higher (P<0.05) in eCG-alhydrogel ewes. In all groups, estradiol concentration showed an increasing trend with time (P<0.05). Estradiol concentration was significantly higher in the 48SR compared with the -48S group; no difference was observed between 24S and -24SR ewes (P>0.05). The findings indicated that in an estrous synchronization protocol, administration of slow- release eCG preparations might improve the fecundity and multiple births in sheep.
