Ovum pick up in mares
Isabel Catalina Velez J. VM MS DACT
Universidad Nacional de Colombia, Bogota
Ovum pick up (OPU) or transvaginal ultrasound-guided follicle aspiration (TVA) is the technique performed in horses to obtain oocytes for intracytoplasmic sperm injection (ICSI). In the horse, conventional in vitro fertilization (IVF) is not successful because low fertilization rates are obtained and results have not been repeatable (1). Ovum pick up has been performed in mares for research purposes for over 20 years and now is being used clinically to obtain offspring from mares that were infertile if conventional breeding techniques were used or in fertile mares bred to stallions with limited semen quality or availability (2).
To perform the technique the mare is put under light sedation and the rectum relaxed. An ultrasound microconvex transducer is fit into a transvaginal probe that accommodates a needle. The needle is passed through the vaginal wall at the fornix into the ovary held by an operator transrectally against the ultrasound transducer to see the follicles on the ultrasound screen. The follicles are aspirated and rinsed several times in order to dislodge the very well attached equine oocytes from the follicular wall while the operator massages the ovary transrectally. For all the manoeuvres that need to be performed to obtain a good number of equine oocytes the operator requires experience and a safe clinical set up to avoid complications with the mare’s health. The complications that have been reported in the literature are hemorrhages from the vessels in the reproductive tract, rectal tears or punctures leading to abdominal infections, ovarian scar tissue and consequently ovarian adhesions or inoculation of bacteria from the vagina in the ovaries with the possible formation of an abscess. Moreover, reactions to the sedation or the drugs used to relax the rectum might happen (2-4). There has been only one report published of a mare’s death caused by internal hemorrhage presumably because of a needle puncture on the left uterine artery (5).
The team at the Equine Fertility Centre (EFC) in Maria Hoop recorded the number of complications with the OPU procedure in 641 aspirations in 177 mares and found only 2.8% (18) of rectal bleeding, 0.4% (3) of transient reaction to the sedation, 0.8% (5) of periovaric bleeding and 0.3% (2) of mares that presented colic after the procedure. These mares had no further complications and recovered within few hours.
The fertility of the mares after the OPU procedure has also been investigated since oocytes are also collected from fertile mares. Pregnancy rates between 70 and 90% have been reported when mares were bred by artificial insemination and pregnancies were detected 14 and 25 days later or embryos were collected (2,6,7). The mares used for these studies had a range of 1 to 17 OPU sessions with only one pre-ovulatory follicle aspirated or multiple follicles aspirated on each sessions. Few mares have been utilized for these fertility studies and mostly only one cycle bred after the OPU sessions. At the EFC 78% (113) mares that have had 1 to 11 OPU sessions got pregnant after embryo transfer, 71% (7) of mares were bred and embryos were recovered within two cycles.