Embryo transfer is an assisted reproduction technique by which an embryo is transferred from the uterus of a donor mare to the uterus of a recipient mare that will carry the pregnancy to term. The embryo is usually recovered from the donor mare by uterine lavage (wash) at around 6 to 8 days after ovulation. The embryo is then placed in the uterus of a synchronized recipient mare.
The success of this procedure depends on the ability to control any of the following factors:
Equipment for Embryo Transfer
Starting an embryo transfer program requires setting-up a specialized laboratory. Embryo transfer equipment is commercially available from most companies selling equine breeding supplies. Apart from the usual equipment used for routine assisted breeding, such as an ultrasound machine, the following is required:
The flushing medium most commonly used for embryo transfer is Dulbecco's phosphate buffered saline (DPBS) supplemented with 10 percent fetal calf serum and antibiotics. This medium is also used to wash and transfer the embryo into the recipient's uterus. The medium may be purchased in liquid or in powder form and reconstituted in the laboratory. As an alternative to DPBS, which is expensive, some practitioners use Lactated Ringers Solution instead.
Prior to attempting embryo recovery, all utensils and media should be warmed to body temperature in an incubator to avoid cold shock to the embryo. All equipment should be either disposable or washed properly and sterilized prior to use. No detergents or disinfectants should be used for washing embryo transfer equipment, since they may leave residues that might compromise viability of the embryo. Equipment is washed with warm tap water only and is then thoroughly rinsed with distilled water. Reusable catheters, tubing and filters should be gas sterilized prior to use.
Separate Foley catheters should be reserved for embryo recovery procedures and not mixed with those used to lavage the uterus of mares with infections.
Choosing Recipients for Embryo Transfer
It is well worthwhile to invest time and money in choosing optimal recipients, as it would be wasteful to invest resources and expertise in breeding a donor mare and recovering an embryo and then place it in the uterus of a mare that could not carry a foal to term. Therefore all mares purchased with the purpose of becoming recipients for an embryo transfer program should be submitted to a complete breeding soundness exam. All mares that make it into the recipient program should pass all aspects of the BSE and have a healthy endometrium (lining of the uterus) when evaluated in a biopsy sample.