Assisted Reproduction Techniques in Horses

The use of assisted reproduction techniques, (ARTs), in horses is comparatively new, becoming more widely used in the past 20 years, when compared to the history in other domestic animals. ART has been used far more extensively in beef and dairy cattle than in horses. This may be in part due to the economic factors playing a factor in cattle industry while horses are mainly used for recreational purposes, and the resistance on the part of some breed associations to accept ARTs as part of their programs. As well, physiological and anatomical differences in horses can make procedures in the horse more complex. ARTs are effective for addressing fertility issues, allowing for increased production of desired genetics not limited to the natural reproductive capabilities of the mares and stallions involved, or allowing breeding of animals that are geographically removed. ARTs include; artificial insemination (AI), oocyte recovery and transfer, embryo transfer, nuclear transfer, a form of cloning, intracytoplasmic sperm injection, which involves in vitro fertilization, including embryo culture, manipulation and transfer. Most of these techniques require veterinary support and supervision for successful outcome.

Artificial Insemination

Artificial insemination occurs when semen from a stallion is harvested and transferred to the mare by artificial means. Semen may be fresh, chilled or frozen. Fresh semen must be used immediately, chilled semen must be used within 24 hours, and frozen semen can be stored and used years later. The semen is inserted by a insemination syringe or pipette into the horse's vagina and through the cervix when the mare is in estrus either prior to ovulation for fresh or chilled semen or immediately after for frozen semen. Multiple inseminations may be necessary to ensure success. This procedure may be performed by a veterinarian or trained professional.

Embryo Transfer 

This procedure requires a veterinarian to perform. Embryos are harvested from a donor mare, whose uterus is flushed a week after ovulation to collect the embryo and inserted in the uterus of a recipient mare. The recipient mare carries the foal to term, gives birth and nurses the foal. Harvested embryos are cooled to 5 degrees celsius. This procedure allows for the genetics of a mare to produce offspring over and above her own natural reproductive capabilities.

Oocyte Transfer

Oocyte transfer is a procedure your veterinarian performs to harvest eggs from a donor mare and place them into the oviduct of a recipient mare where insemination can take place, usually by artificial insemination. While this procedure also allows for the spread of desired genetics from a mare, it also allows offspring to be produced from a mare that is unable to become inseminated, produce fertilized embryos or carry pregnancy to term. 

Intracytoplasmic Sperm Injection, Embryo Culture, In Vitro fertilization

Thi procedure is performed by a veterinarian to develop a viable embryo outside the natural environment. Your veterinarian will harvest oocytes from a mare, inject them with semen, mature the embryo in a laboratory for several days and then freeze the embryos for future use or transfer them to a recipient mare.

Because horses are often chosen for breeding based on performance or confirmation attributes as opposed to fertility, the success of ARTs in horses can be negatively impacted. 

ART procedures allow for genetics from multiple geographic regions to be shared and increases the spread of desired genetics by allowing desirable genetics from specific mares and stallions to be spread to offspring beyond that which could occur naturally. These techniques are improving as more experience with ART in horses is gained. 

Mares that are inseminated or experience oocyte or embryo transfer should be monitored for signs of pregnancy and provided appropriate prenatal care.

Costs range from $500 to $5,000 or more depending on the procedure used and the number of attempts required for success. Veterinary costs, donor stallion costs, donor mare costs, laboratory, shipping, and timing and coordination expenses all factor into the total cost of ART.

ART can be very expensive and time and resource-consuming, and success rates can be limited. There is no guarantee that live offspring will result from ART efforts. 

There are ethical considerations with these procedures; upsetting the natural balance of genetics in the population could potentially cause unpredicted issues in the species, with certain genetics becoming more prevalent and disease or illness associated with these genetics becoming disproportionate in the population. These issues have been largely avoided in the cattle industry and therefore careful monitoring of results in the equine industry should mitigate this possibility.

In addition, some breed associations are not receptive to these technologies, ensure you investigate your breed association regulations prior to utilizing ARTs.

ARTs can be a useful tool to circumvent infertility, or spread desired genetics in the population. In addition, it can be effective at reducing stress, injury, and disease in horses being transported or participating in natural breeding.