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Description and genetic analysis of three sets of monozygotic twins resulting from transfers of single embryos to recipient mares

Semira S. MancillDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Glenn Blodgett6666 Ranch, PO Box 130, 1102 Dash For Cash Rd, Guthrie, TX 79236.

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Robert J. ArnottSaint John Valley Veterinary Services Inc, 192 Broadway St, Woodstock, NB E7M 6B3, Canada.

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Marco AlvarengaDepartment of Animal Reproduction and Veterinary Radiology, Veterinary School, University of Sao Paulo State, UNESP, Botucatu, SP 18618-000, Brazil.

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Charles C. LoveDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Katrin HinrichsDepartment of Large Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Abstract

Case Description—3 sets of monozygotic twins resulting from transfers of single embryos to recipient mares were examined.

Clinical Findings—In all 3 recipient mares with twin pregnancies, only 1 embryonic vesicle was detected before day 25 of gestation. In 1 recipient mare, 2 apparent adjacent vesicles, each containing an embryo with a heartbeat, were visualized on ultrasonographic examination on day 37 of gestation. The other 2 recipient mares underwent ultrasonographic examination on day 30 of gestation, at which time only 1 vesicle and embryo was identified. In these latter 2 recipient mares, however, a thorough ultrasonographic examination for a second conceptus on day 30 had not been performed, as only 1 embryo had been transferred and visualized on early ultrasonographic examination.

Treatment and Outcome—All twin pregnancies resulted in death of both fetuses. Genetic analysis confirmed that each set of monozygotic twins originated from the transferred embryo.

Clinical Relevance—Monozygotic twin pregnancy may occur after embryo transfer; thus recipient mares should be examined thoroughly for multiple conceptuses, especially between 25 and 30 days of gestation. At this time, the allantoides of monozygotic twins should be visible ultrasonographically and effective management may still be possible.

Abstract

Case Description—3 sets of monozygotic twins resulting from transfers of single embryos to recipient mares were examined.

Clinical Findings—In all 3 recipient mares with twin pregnancies, only 1 embryonic vesicle was detected before day 25 of gestation. In 1 recipient mare, 2 apparent adjacent vesicles, each containing an embryo with a heartbeat, were visualized on ultrasonographic examination on day 37 of gestation. The other 2 recipient mares underwent ultrasonographic examination on day 30 of gestation, at which time only 1 vesicle and embryo was identified. In these latter 2 recipient mares, however, a thorough ultrasonographic examination for a second conceptus on day 30 had not been performed, as only 1 embryo had been transferred and visualized on early ultrasonographic examination.

Treatment and Outcome—All twin pregnancies resulted in death of both fetuses. Genetic analysis confirmed that each set of monozygotic twins originated from the transferred embryo.

Clinical Relevance—Monozygotic twin pregnancy may occur after embryo transfer; thus recipient mares should be examined thoroughly for multiple conceptuses, especially between 25 and 30 days of gestation. At this time, the allantoides of monozygotic twins should be visible ultrasonographically and effective management may still be possible.

Contributor Notes

Dr. Mancill's present address is SDP Buffalo Ranch, 1790 FM 2871, Fort Worth, TX 76126.

Supported in part by the Link Equine Research Fund, Texas A&M University.

Presented in abstract form at the Annual Convention of the 54th American Association of Equine Practitioners, San Diego, December 2008.

Address correspondence to Dr. Mancill (semiradvm@gmail.com).