Abstract
In Portugal, there is much interest in the so-called assisted reproductive technologies as applied to horse breeding, namely at the semen cryopreservation and Artificial Insemination levels. The interest for embryo transfer in mares has also emerged despite several problems associated with this technique, such as the resistance of most breed registration authorities in accepting progeny begot by this method. The intention of this study was to evaluate the accuracy of embryo recovery techniques at a small facility and to consider the feasibility of its implementation for embryo transfer. Seven mares were alternatively inseminated in 13 successive oestrous cycles with fresh semen from 3 stallions of varying fertility. Ovulation was left to occur spontaneously, and embryo recovery was carried out by non-surgical uterine flushing using both a closed flushing system (RS1) and an open flushing system (RS2). A total of 13 embryo collection attempts were performed on 7 possible positive pregnancy diagnoses with a rate success of 57.14% (4/7). Our preliminary results showed that the open flushing recovery system gives the best results and the high success recovery rate suggests that the technique of embryo transfer can be fully implemented even in facilities with limited resources.
Highlights
In several mammalian species embryo recovery, embryo cryopreservation and embryo transfer are routinely used in animal husbandry
Embryo recovery rates vary greatly between 6 and 9 days after ovulation: Squires [1] reported a collection rate of 62% on day-6 embryos, a value slightly lower than the recovery rates obtained at days -7, -8 and -9 embryos (76%, 74% and 81%, respectively)
All semen samples were obtained during the breeding season (February to July) and the ejaculates used to inseminate the mares as described before [8]
Summary
In several mammalian species embryo recovery, embryo cryopreservation and embryo transfer are routinely used in animal husbandry. In contrast in the equine these techniques are not common clinical procedures, due to the rejection of embryo transfer as a reproductive technique by the majority of horse registries. This situation has been changed and numerous studies have emerged in this field in order to obtain foals from older and problematic mares, or to increment production from genetically superior mares. Factors that affect the success of embryo collection include the number of ovulations, the age of the donor mare (as well as its reproductive history), the quality of stallion semen used, and, embryo size and stage of embryo development at the time of recovery [2]. For commercial purposes the optimal time for embryo collection is day 7 or 8 after detection of ovulation, but it results in embryos with large and variable diameters [3] It has been advanced that flushing on day 6 brings in a significant drop in embryo recovery rate because, in some mares, the embryo has not yet reached the uterus and/or that embryonic development rates differ between individual embryos [4, 5]
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