Abstract

The purpose of this study was to investigate the effects of gonadotropin-releasing hormone (GnRH) administration on the induction of multiple births in synchronized Afshari ewes. 16 cycling, multiparous fat-tailed Iranian Afshari ewes, weighing 66.5 ± 2.5 kg, were used in the trail. Estrus was synchronized using controlled internal drug release CIDR’s; inserted for 14 days. Pregnant mare serum gonadotrophin(PMSG) (300 IU) was injected to ewes a day before CIDR removal. The ewes was randomly allocated to two groups (n = 8). Synchronization treatment was initiated with a week interval in two groups (weeks 1 and 2). 24 h following CIDR removal (day 1), GnRH (50 µg) was administered to half of each group ewes (GnRH and control groups), and ewes mated with the proven rams. Pregnancy was diagnosed with the aid of transabdominal ultrasonograpy 30 days after mating. Ovarian follicular activity was monitored with the aid of transrectal ultrasonograpy on the days of CIDR removal and at estrus (approximately day 1). Following PMSG treatment, the mean number of large follicles on total ovaries increased from CIDR removal to estrus 1.48 ± 0.71 vs. 2.85 ± 0.82 (P < 0.05). Lambing rate in GnRH group (162.5%) was higher (P < 0.05) compared to the control group (125%). The mean weights of lambs born in the GnRH and control groups were 5.5 ± 0.1 and 5.2 ± 0.1, respectively.

Key words: GnRH, estrus synchronization, Afshari, ewe, lambing rate.