Oestrus synchronization in small ruminants: A review

Oestrus synchronization is a reproductive management tool that is particularly useful in artificial insemination and embryo transfer programmes. It manipulates female's oestrous cycles with one or more hormones like melatonin implants, progestogens, gonadotropins/GnRH and prostaglandins alone or in combination. The use of progestogen or progesterone in combination with equine chorionic gonadotropin (eCG) and PGF₂α usually produces a high rate of oestrus. Pharmacological doses of gonadotropin-releasing hormone (GnRH) in conjunction with intravaginal sponges to induce ovulation have been evaluated and a single injection of GnRH (@ 0.008 mg) at standing oestrus following intra-vaginal sponge (progesterone, 300 mg, 12 d) and PMSG treatment increased the pregnancy rate. The male effect represents a viable and inexpensive alternative as a co-treatment in melatonin implants or progesterone-based synchronization schemes for anoestrous females. However, of all the oestrus synchronization protocols in use to date, not a single one fulfils all expectations concerning predictability and reliability of the response. The variability in number of ovulation remains the main drawback and the efficacy of synchronization depends on many factors, including season, exposure to males, breed, and age among others. Research in oestrus synchronization is essential to provide evidence that user interest merit efforts to provide labelling for minor species on desired pharmaceutical products and to establish optimal doses and agents to use for favourable synchrony and fertility. In developing countries, the nomad systems, the educational levels of farmers and the cost of oestrus synchronization are some of factors which explain partially why the use of modern reproductive techniques that are in practice in developed countries are not applied on a commercial scale.