How Equine ICSI Works
A plain-language guide to oocyte pickup, maturation, sperm injection, embryo culture, freezing or transfer, recipient mares, and pregnancy checks.
Written by Solo Select Horses Reviewed July 16, 2026
The short answer
Equine ICSI is a laboratory-assisted breeding process. A veterinarian collects oocytes from a donor mare by transvaginal aspiration, a laboratory matures the recovered oocytes, and an embryologist injects one sperm cell into each mature oocyte. Developing embryos can then be frozen or transferred into synchronized recipient mares.
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The four biological participants
The donor mare supplies the oocytes. The stallion supplies the sperm. The resulting embryo carries genetics from those two horses. A recipient mare carries the pregnancy, delivers the foal, and normally raises it through weaning without contributing genetics to the foal.
Veterinarians and embryologists perform different parts of the work. Oocyte collection is a veterinary procedure; maturation, injection, and culture occur in a specialized laboratory; embryo transfer and pregnancy evaluation return to the veterinary and recipient-management teams.
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The process from follicle to embryo
The donor mare is examined and prepared under veterinary direction. During oocyte pickup, often shortened to OPU, follicles are visualized with ultrasound and aspirated while the mare is sedated. The laboratory identifies and matures the recovered oocytes.
An embryologist selects one sperm cell and injects it into each mature oocyte. The injected oocytes are monitored as they cleave and develop. Embryos that reach the appropriate blastocyst stage may be prepared for transfer or vitrified for storage.
- Veterinary examination and breeding plan
- OPU or follicular aspiration
- Oocyte recovery and maturation
- One sperm injected per mature oocyte
- Embryo culture to the blastocyst stage
- Fresh transfer or vitrification
- Recipient transfer and pregnancy checks
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What ICSI changes—and what it does not
ICSI can use very small quantities of semen and can create opportunities for mares and stallions that are difficult to breed conventionally. It can also let a donor mare remain out of gestation and may produce more than one embryo from an aspiration.
It does not guarantee that follicles yield oocytes, that oocytes mature, that injected oocytes develop into blastocysts, or that a transferred embryo establishes and maintains a pregnancy. Each stage has its own denominator and its own sources of variation.
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Where Solo Select and GeneTech connect
Solo Select coordinates the donor-side plan, semen and aspiration logistics, recipient availability, pregnancy management, and foaling path. GeneTech performs the specialized ICSI laboratory work. The exact handoff depends on the donor mare, semen, laboratory schedule, embryo plan, and current service agreement.
A customer should know who is responsible for each handoff before the aspiration date: the attending veterinarian, Solo Select, GeneTech, semen owner or station, transporter when applicable, and recipient team.
Common Questions
Direct answers
- What does ICSI stand for in horse breeding?
- ICSI stands for intracytoplasmic sperm injection: one sperm cell is injected directly into the cytoplasm of a mature oocyte.
- Is ICSI the same as embryo transfer?
- No. ICSI is the laboratory fertilization method used to create an embryo. Embryo transfer is the later step of placing an embryo into a recipient mare.
- Does ICSI require a recipient mare?
- An ICSI embryo needs a mare to carry the pregnancy. That may be a synchronized recipient mare selected for transfer after the embryo is created or warmed.
Sources and Methodology
Where these answers come from
GeneTech-specific statistics are identified as partner-reported operating figures. General medical and biological explanations use veterinary or primary technical sources. Percentages should not be compared unless their denominator, population, endpoint, and reporting period match.