G. Aria

Clinical use of twice daily injections of buserelin acetate to induce ovulation in the mare.

The difficulties in the prediction of ovulation time in the mare, together with the increasing use of cooled and frozen semen for artificial insemination, have stimulated investigators to search for methods for induction of ovulation. These methods are essentially based on exogenous administration of one of three hormones directly or indirectly involved in the mechanism of ovulation: hCG (Human Chorionic Gonadotrophin), CEG (Crude Equine Gonadotrophin) (Duchamp et al., 1987), or GnRH (Gonadotrophin-releasing hormone). Repeated administration of hCG, which is a heterologous glycoprotein for mares, may stimulate an immune response able to neutralise the effect of the hormone (Roser et al., 1979). Although CEG has not shown this negative side effect, it is not found on the market, and purified extracts are produced and utilised only by few research groups. GnRH, physiologically released in a pulsatile manner, and its analogues have been tested for induction of ovulation in oestrous mares either by repeated injections at given time intervals (Palmer and Quellier, 1988) or as slow-release subcutaneous implants. For this purpose, a slowrelease subcutaneous implant containing the synthetic GnRH analogue deslorelin acetate (OvuplantA) is successfully used in United States and Australia (Meinert et al., 1993; Meyers et al., 1997). The response to OvuplantA administration was similar to that obtained using hCG. However, this formulation is currently not available in the Italian and European market. The efficacy of buserelin, a GnRH analogue also commercialised in Italy, has been recently investigated for induction of ovulation in the mare. The administration of a single dose has not yielded encouraging results (Vidament et al., 1992). On the other hand, Battut et al. (2001) observed that most mares treated twice daily with intravenous (IV) administration of 20 or 40 mg of buserelin ovulated within 48 h. The aim of our study was to evaluate the clinical efficacy of repeated administration of 40 mg buserelin for induction of ovulation in the mare, as compared to a single administration of 2500 IU hCG or a placebo.