The utilization of embryo transfer in the horse has progressed steadily over the past couple of decades. Nevertheless, numerous unique biological features as well as technical problems have restricted its prevalent use in the horse as compared with the other industry. Reasons that affect embryo recovery include the quality of sire’s semen, age of the donor, day of recovery, and the number of ovulations. Usually, embryo recoveries are performed 7 or 8 days after ovulation if not the embryos are to be frozen, in which case recovery is performed 6 days after ovulation. The majority of the embryos are recovered from single-ovulating mares. For the reason that there is no commercially available hormonal preparation for inducing multiple ovulations in the horse, equine pituitary extract has been utilized to boost the number of ovulations in treated mares. However, FSH of ovine or porcine origin is relatively unproductive in inducing multiple ovulations in the mare. Factors made known to affect pregnancy rates after embryo transfer include embryo quality, synchrony of the donor and recipient, method of transfer, and management of the recipient.

One of the major developments in equine embryo transfer over the last several years is the capability to store embryos at 5 degrees Celsius and thus send them to a centralized station for transfer into recipient mares. Embryos are collected by practitioners on the farm, cooled to 5 degrees Celsius in a passive cooling unit and shipped to an embryo transfer station without a major decrease in fertility. Nevertheless, growth in developing techniques for freezing equine embryos has been slow. Currently, only small, Day-6 equine embryos can be frozen with reasonable achievement. Additional researches are necessary to hone the techniques for freezing embryos collected from mares 7 or 8 days after ovulation. Demand for the development of assisted reproductive methods in the horse has enlarged dramatically. Collection of equine oocytes by transvaginal, ultrasound-guided puncture and the transfer of these oocytes into recipients are being used to produce pregnancies from donors that had previously been incapable of providing embryos. In vitro fertilization, on the other hand, has been essentially unsuccessful in the horse. Intra-cytoplasmic sperm injection is an option to in vitro fertilization that has shown promise. Nonetheless, culture conditions for in vitro-produced embryos appear to be insufficient. The continued demand for assisted reproductive technology will possibly result in the further development of techniques that is suitable for use in the horse.

Improvement of assisted reproductive technologies in horses has been relatively slow compared to other domestic species, namely ruminants and pigs. The limited availability of abattoir ovaries and the lack of interest from horse breeders and breed associations have been the main reasons for this delay. Progressively though, the technology of oocyte maturation in vitro has been established. Embryo culture was initially performed in vivo, in the mare oviduct or in the surrogate sheep oviduct, to achieve the highest embryo development, in the range of 18-36% of the fertilized oocytes. Consequently, the analogous improvement of in vitro oocyte maturation conditions and embryo culture media has permitted high rates of embryo development from in vitro matured and in vitro cultured embryos, ranging from 5 to 10% in the early studies to up to 38% in the latest ones. From 2003, with the birth of the first cloned equids, the technology of somatic cell nuclear transfer has also established due to improvement of the basic steps of embryo production in vitro, including cryopreservation. Pregnancy and foaling rates are still estimated based on a small number of in vitro produced equine embryos transferred to recipients. The largest set of data on non-surgical embryo transmission of in vitro produced embryos, from both abattoir and in vitro-matured Ovum Pick Up (OPU) oocytes, and from somatic cell nuclear transfer, has been gathered in the laboratory. The data revealed that equine embryos produced by OPU and then cryopreserved, can achieve up to 69% pregnancy rate with a foaling rate of 83%. These percentages are lowered to 11 and 23%, respectively, for cloned embryos. Thus, widespread evidence exists that in vitro matured equine oocytes can efficiently develop into viable embryos and offspring. The increasing variety of equestrian sports has led to a constant rise in the number of horse breeds and breed registries. In addition to the trend towards more and smaller breed registries, there is another trend towards an international expansion of the bigger established sport horse breeds. Regional breeds, at least in smaller countries, may no longer be able to run an independent breeding program. The typical horse breeder, in the future, will be a female and qualified in equestrian sports. Artificial insemination (AI) mainly with fresh or cooled-transported semen has become a major breeding tool, allowing breeders to benefit from the best stallions of most breeds. Recent AI techniques such as low-dose insemination may remain restricted to individual stallions and also the interest of breeding programs in sex determination of foals via semen sorting is limited. Embryo transfer and associated methods, although allowed by most breeds, have not contributed significantly to genetic progress in sport horses so far. A potential use of cloning may be to produce gonad-intact copies from geldings that have performed to a superior level. With a more open and international structure of horse veterinary curricula and continuing professional education programs should emphasize breeding and increased use of AI, equine reproduction and biotechnology.