The present study compared the occurrence of oestrus behaviour and ovulation in response to the insertion of CIDR devices plus a classical treatment with equine chorionic gonadotrophin (eCG; single dose at CIDR removal) or alternative treatments with gonadotrophin-releasing hormone (GnRH, either in a single dose at 56 hr after CIDR removal, or in one dose at CIDR insertion and another dose at 56 hr after CIDR removal). The appearance of oestrus behaviour during reproductive season ranged between 84% and 95% and all females showing oestrus signs had subsequent ovulations. The response, during seasonal anoestrus, was similar in the group treated with eCG, but less than half of the females in the groups treated with GnRH showed oestrus signs in response to the treatment, although more than 80% of them showed resumption of ovulatory activity after the treatment. In conclusion, protocols based on GnRH administration offer similar yields to eCG-based protocols during the reproductive season but occurrence of oestrus in response to GnRH-based treatments is highly compromised during seasonal anoestrus.
Keywords: GnRH; IDR; oestrus-synchronization; ovulation; sheep.
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