Plain-Language Reference
Equine Embryo Transfer and Recipient Mare Glossary
Clear definitions for donor mare, recipient mare, embryo flush, ICSI, oocyte aspiration, synchronization, cryopreservation, and related terms.
Written by Solo Select Horses Reviewed July 15, 2026
The short answer
This glossary defines common equine reproduction terms in plain language. It is educational, not a substitute for advice from the veterinarian, laboratory, registry, or contract responsible for a specific breeding plan.
01
Mares and reproductive roles
- Donor mare: the mare that provides the oocyte and is the foal's genetic dam.
- Recipient mare: the mare that receives an embryo, carries the pregnancy, delivers the foal, and normally nurses it until weaning.
- Synchronization: veterinary management used to align a recipient mare's reproductive stage with the embryo's developmental stage.
- Ovulation: release of an oocyte from the ovary.
02
Embryos and procedures
- Embryo recovery or flush: a veterinary procedure used to recover an embryo from the donor mare's uterus.
- Embryo transfer: placement of an embryo into a suitable recipient mare.
- Fresh embryo: an embryo handled for transfer without first being cryopreserved.
- Cryopreservation: preservation at very low temperature for potential future use.
- Warming or thawing: the controlled process of preparing a cryopreserved embryo for evaluation and possible transfer.
03
ICSI terminology
- Oocyte: the female reproductive cell, commonly called an egg.
- Oocyte aspiration: veterinary collection of oocytes from follicles in the donor mare's ovaries.
- ICSI: intracytoplasmic sperm injection, a laboratory technique in which one sperm cell is injected into an oocyte.
- Embryo culture: controlled laboratory monitoring of a fertilized oocyte as it develops.
04
Pregnancy and program terms
- Pregnancy check: a veterinary examination used to evaluate pregnancy status and development.
- Heartbeat check: a pregnancy examination at which the veterinarian evaluates embryonic or fetal cardiac activity at the appropriate stage.
- Live foal guarantee: a contract term whose definition, conditions, duration, exclusions, and remedy vary by program.
- Recipient mare lease: a contract granting temporary use of a recipient mare under stated transfer, care, return, fee, and ownership terms.
- Foaling: the process of a mare giving birth.
- Weaning: the managed separation of the foal from the mare's milk and maternal care.