Real World Approaches to ART in Practice

Several Artificial Reproductive Technologies (ART) have been used in horses for a few decades, starting with artificial insemination and progressing to embryo transfer, in-vitro produced embryos, and cloning.

Currently artificial insemination is the most common ART used for breeding horses (except for thoroughbreds) and embryo flushing and transfer is the most common way to obtain more than one offspring per mare per season.

Several Artificial Reproductive Technologies (ART) have been used in horses for a few decades, starting with artificial insemination and progressing to embryo transfer, in-vitro produced embryos, and cloning. Currently artificial insemination is the most common ART used for breeding horses (except for thoroughbreds) and embryo flushing and transfer is the most common way to obtain more than one offspring per mare per season. During the last 5 years, with the increase in success rates of in vitro fertilization using ICSI (Intracytoplasmic sperm injection) there has been a significant expansion in the use of aspiration of immature oocytes for in vitro embryo production for commercial purposes. This procedure is called TVA (Transvaginal Aspiration) or OPU (ovum pick-up) and recently this practice is getting more and more common, switching from being performed exclusively at specialized centers to becoming available for practitioners in the field.

The TVA of oocytes is performed with mares restrained in stocks, standing and under sedation (usually with a combination of detomidine and butorphanol). The procedure requires the use of a transvaginal ultrasound probe with a needle guide, a tubing system, and a pump. Usually, 2 practitioners will be on the back of the mare; one with the arm in the rectum fixing the ovaries and the other one manipulating the needle to puncture and scrape the follicles. A third person will be infusing the flush media into the follicles. For the procedure to be safe and successful a high level of communication and coordination between all the team members is required. Each follicle is aspirated and flushed several times (6-10) to be able to obtain the oocyte. The procedure is repeated for every follicle visible on ultrasound.

Not every follicle will yield an oocyte. The reported recovery rate of oocytes on TVA varies from 10-30% at the beginning of the learning process to over 50-60% in practices with more experience. The recovery rate can be influenced by individual mare, breed, age and size of the follicles. There is a learning curve for this procedure; practitioners that are new to it start with low recoveries and success significantly increases with practice. Some colleagues suggest that a minimum of 100 aspirations are needed to become successful and confident with TVA.

This procedure is usually very safe but severe complications such as hemorrhage, abscesses, or rectal tears have been reported in a few occasions.

The TVA is more invasive than a traditional embryo transfer and there is an expected level of inflammation in the mares after the procedure, particularly detectable using abdominocentesis that may be subclinical or clinically evident. Clinical signs of pain or discomfort in the first 24hrs are not uncommon.

The number of oocytes obtained per procedure is highly variable but reports show an average 5-13 oocytes per aspiration. There are many factors affecting successful embryo production and one of the most important is the number of oocytes obtained in the aspiration, different reports show an average of 0.6-2 blastocysts per aspiration. The team at Utrecht University reported that one or more blastocyst will be obtained in 78% of the aspirations.

Most embryos are frozen or vitrified without a significant loss in viability, this is an advantage of in-vitro embryo production (IVEP)when compared with in vivo produced embryos.

The success rate for pregnancy has been reported to be between 70-78%, but some of those pregnancies will be lost before foaling (approximately 15%). Based on reported success rates, an in vitro produced embryo will generate a foal 50-60% of the time (Claes and Stout 2020).

An important benefit of in vitro produced embryos is that of time efficiency; TVA/ICSI is a quick procedure and doesn’t require the cycle of the mares to be monitored. Additionally, the procedure can be performed year-round and beyond the breeding season.

In vitro production of embryos is becoming the most important way to produce foals out of mares with severe fertility issues (chronic infections, incompetent cervix or infertility of unknown origin) or very busy performance schedule. This technique also provides the opportunity to generate embryos from stallions with very low availability of sperm (low quality or deceased stallions). With the growth trend of these procedures, probably IVEP will be soon the most common way to obtain multiple embryos per year from the same mare.

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