Superovulating mares with gonadotrophins : recent developments and state of the art

Abstract

In domestic species the aim of superovulation treatments is to increase natural ovulation rates in order to produce several healthy embryos in a single oestrus cycle and to then transfer these embryos into recipient females. Actually, in equine species, no commercial preparation is available for superovulation. Indeed, gonadotrophins licenced for other species are not effective in mares and responses in mares, to superovulation treatments with equine FSH (eFSH) are heterogeneous.

In mares, superovulation treatments must use eFSH and the heterogeneity of response can adversely affect the number of preovulatory follicles, the number of ovulations and the number of transferable embryos. As for other domestic species, there are multiple reasons for this variability. Among them, unsatisfactory dosage regimens for eFSH that can cause unwanted effects on follicular growth, ovulation and plasma hormone levels and decrease embryo production. In this context, our studies in mares have determined the relationships between impaired follicular growth and modified plasma hormone levels and the factors responsible for the decrease in embryo production. An appropriate dosage regimen for eFSH has been proposed on the basis of FSH plasma levels that can induce superovulation without unwanted side effects. This dosage regimen corresponds to 50% of the daily production rate of the native hormone in an ova riectomized mare. On the basis of these data, a treatment regimen has been suggested, with the aim of producing 3 to 4 ovulations and 1,8 to 2,5 embryos per oestrus cycle. Finally, several strategies have been suggested which could improve the effectiveness of eFSH treatments in mares.

Nevertheless, the future commercialization of an equine FSH preparation is questionnable because the number of pituitary glands available from slaughterhouses is limited, there are strong health requirements associated with this type of product and this preparation has to be species specific.