"We know that twinning has a profound impact on the mare," said Karen Wolfsdorf, DVM, Dipl. ACT, of Hagyard Equine Medical Institute. "The presence of twins post-fixation (after the embryonic vesicle becomes stationary on about the 16th day after ovulation and fertilization) can be devastating economically with the potential loss of both fetuses and a reduced rate of fertility the following season. Wolfsdorf and her colleagues have been using a novel reduction technique for about four years that she described at the Hagyard Bluegrass Equine Reproduction Symposium 2006, which was held Oct. 18-21 in Lexington, Ky.

Veterinarians generally attempt to detect and crush the extra vesicle in a twinning case by 14 days of gestation, but if the twins are detected any later than that, it can be harder to reduce the second embryo. Post-fixation reduction techniques have been restricted to manual crushing of one vesicle if the vesicles are bilateral, meaning they aren't attached to one another--otherwise, they are unilateral, and it can be difficult to reduce one without damaging the other.

Other methods include transvaginal (via the vagina) ultrasound-guided aspiration, which has had variable results depending on age of the gestation and the veterinarian's technical ability, and transabdominal (performed through the abdominal wall) ultrasound-guided aspiration, after which only 30% of the remaining pregnancies produce normal-sized, healthy foals.

Wolfsdorf and colleagues have been using craniocervical dislocation--dislocation of the first cervical vertebrae from the cranium--of the twin transrectally or within the abdomen to ensure twin reduction and minimizing interference with the remaining fetus. Ideally, she performs this procedure between 55 and 110 days of gestation--at 55-90 days using the transrectal approach and 65-110 for the intra-abdominal approach.

For the transrectal approach, Wolfsdorf restrains and tranquilizes the mare in stocks, and she administers flunixin meglamine (Banamine, as an anti-inflammatory). "The key point is uterine relaxation," she said. "We do transrectal ultrasound to determine which (uterine) horn they (the embryonic vesicles) are in. Most are unilateral, and we want to try and go for the vesicle that is at the cranial aspect, up closest to the ovary," or the less viable fetus.

She isolates the fetus that she wants to reduce, at which time it's important to hold on tightly, as she might end up reducing both if she drops it and then retrieves the wrong one. Wolfsdorf locates the embryo's head, and she breaks down the ligaments until she feels a distinctive space between the head and the cranial cervical vertebrae.

After performing the procedure, she prescribes anti-inflammatories and a double dose of altrenogest for 30 days to maintain the remaining fetus. Wolfsdorf checks the pregnancy for the demise of the manipulated fetus every two weeks (visible as loss of heartbeat on ultrasound), and she continues to monitor the pregnancy for growth of the remaining fetus.

The intra-abdominal approach is similar, only Wolfsdorf uses procaine penicillin and gentocin systemically and anti-inflammatories prior to the surgery. She performs the procedure via a standing flank laparotomy incision, after which double-dose altrenogest is administered, and it is decreased after 30 days to a single dose for the duration of the pregnancy. She also administers penicillin, Banamine, and gentocin for three days following the procedure, and she prescribes trimethoprim sulfa for a week. Post-surgical complications can include abortion of both fetuses and incisional infection, but Wolfsdorf said that resolution of these infections generally occur with minimal scarring.

"We've stopped performing the procedure transrectally," she said, because it can be difficult to find and hold on to the fetus from the transrectal angle. "It's much easier to do a flank incision.

"Our rationale is to try and get to the fetus before placental formation is complete and therefore produce a single normal-sized, healthy foal that has the ability to use the entire endometrial surface and grow to its full potential," said Wolfsdorf.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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