Equine embryo transfer: the effect of semen processing and donor mare management on recovery rates

Embryo transfer (ET) is a biotechnology that allows to get more than one foal from a single mare during a breading season and also to prevent the removal of mares from their competition careers. Nevertheless, to achieve a successful outcome, the association of many factors must be considered, such as the management of donor and recipient mares, the stallions and the veterinarian´s experience. In this context, this study aimed to evaluate (1) if some of characteristics related to the donor mares (e.g. breed and the reproductive status, may influence the embryo recovery; (2) if different donor mares location may have impact in breeding programs; (3) the effect of some reproductive techniques and embryo transfer methodologies. For such purpose, 156 uterine flushes and 88 embryo transfers were performed. Higher embryo recovery rates at day 8 (61.5%) and an overall pregnancy rate of 62.2% were obtained. An influence of the month of the year (P=0.04) and of the type of semen (fresh or frozen; P=0.03) on the number of positive embryo collections were identified. The use of fresh semen for donor mares’ insemination and recovery at day 8 increased the number of embryos that were collected during this period, although lower results were obtained in July-August. No other significant effects upon the remaining determinants under testing were observed, although stallions were responsible for inducing 11% of the variability within embryo recovery rates. These results should be considered in mare embryo transfer centres.