title: Description and genetic analysis of three sets of monozygotic twins resulting from transfers of single embryos to recipient mares.
abstract: METHODS
  3 sets of monozygotic twins resulting from transfers of single embryos to recipient mares were examined.
  
  
  RESULTS
  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.
  
  
  RESULTS
  All twin pregnancies resulted in death of both fetuses. Genetic analysis confirmed that each set of monozygotic twins originated from the transferred embryo.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843, USA. semiradvm@gmail.com
authors.forename: Semira S
authors.initials: SS
authors.lastname: Mancill
authors.forename: Glenn
authors.initials: G
authors.lastname: Blodgett
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Arnott
authors.forename: Marco
authors.initials: M
authors.lastname: Alvarenga
authors.forename: Charles C
authors.initials: CC
authors.lastname: Love
authors.forename: Katrin
authors.initials: K
authors.lastname: Hinrichs
mesh_terms: D000818:Animals; D004624:Embryo Transfer / Q000662:veterinary*; D005260:Female; D006736:Horses / Q000235:genetics*; D008297:Male; D010920:Placenta; D011247:Pregnancy; D038522:Twinning, Monozygotic