OPU and Follicular Aspiration in Mares
What breeders should know about transvaginal oocyte pickup, sedation, ultrasound guidance, recovery, scheduling, and veterinary risk discussions.
Written by Solo Select Horses Reviewed July 16, 2026
The short answer
Oocyte pickup, or OPU, is a veterinary procedure in which follicles in a sedated donor mare's ovaries are visualized with ultrasound and aspirated through a guided needle to recover oocytes. The recovered oocytes are then identified, prepared, and sent into the ICSI laboratory process.
01
Before aspiration
The veterinarian reviews the mare's health and reproductive status, examines the ovaries, and determines whether and when aspiration is appropriate. Facility instructions may address feed, medications, transportation, paperwork, and semen or laboratory coordination.
The expected follicle count is not the number of guaranteed oocytes. Recovery, maturation, and later embryo development are separate outcomes.
02
During OPU
The mare is restrained and sedated under veterinary supervision. With transvaginal ultrasound guidance, the veterinarian advances a needle into selected follicles and aspirates their contents for the laboratory team to search for oocytes.
This description is educational, not a procedure protocol. Technique, medications, monitoring, candidacy, frequency, and risk management belong to the attending veterinarian.
03
Material risks
OPU complications are uncommon, but the procedure is invasive and is not risk-free. Published complications include peritonitis, ovarian inflammation or abscess, hemorrhage or blood-vessel injury, rectal injury, fever, colic, and rare fatalities.
A 2025 Journal of Equine Veterinary Science report combined a practitioner survey with field data from more than 14,000 transvaginal aspirations. Major complications occurred in approximately 1 in 1,000 procedures in the survey estimate and 1 in 375 procedures in the field dataset. Those group rates do not predict the risk for an individual mare; the attending veterinarian should explain the mare-specific risks, alternatives, aftercare, and warning signs before consent.
04
Recovery and repeat sessions
Recovery instructions depend on the mare and procedure. Ask what the team will monitor, when the mare may travel or return to work, which signs require a call, and when a repeat examination is planned.
Whether and how often to repeat OPU is an individual veterinary decision. A breeder should not infer a safe schedule from another mare's experience or a social-media result.
05
Questions for the veterinarian
- Why is OPU appropriate for this mare?
- What are the material risks and alternatives?
- How will she be sedated and monitored?
- What should happen before and after the procedure?
- When may she travel or resume training?
- How will complications be recognized and handled?
- When would another aspiration be considered?
Common Questions
Direct answers
- Is a mare sedated for OPU?
- OPU is performed with veterinary restraint, sedation, monitoring, and ultrasound guidance. The attending veterinarian should explain the specific protocol for the mare.
- Does every aspirated follicle produce an oocyte?
- No. Follicles aspirated and oocytes recovered are different counts, and recovered oocytes must still mature before injection.
- Can OPU be repeated?
- Repeat aspiration may be considered, but frequency and suitability must be decided by the attending veterinarian for the individual mare.
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.
- GeneTech: ICSI process
- UC Davis Center for Equine Health: OPU and ICSI overview
- Journal of Equine Veterinary Science (2025): complications associated with equine transvaginal follicle aspiration
Practitioner survey plus field results from more than 14,000 procedures; reports uncommon but potentially serious infectious and traumatic complications.