title: Factors affecting live foal rates of Thoroughbred mares that undergo manual twin elimination.
abstract: BACKGROUND
  Mares diagnosed with twin vesicles at 13-17 days after ovulation commonly have one of 2 vesicles manually reduced. It is not known whether vesicle location (adjacent vs. nonadjacent), mare age, mare reproductive status, parity, month of breeding or mare plasma progesterone concentration affects live foal rates.
  
  
  OBJECTIVE
  To determine factors associated with a positive outcome (live foal) in mares undergoing manual twin reduction between 13 and 17 days post ovulation when performed by a single operator.
  
  
  METHODS
  Retrospective case-control study.
  
  
  METHODS
  Breeding records and the Jockey Club records of registered Thoroughbreds were used to evaluate factors affecting the outcome of pregnancies in mares undergoing twin elimination and mares with singleton pregnancies. Thoroughbred mares with twin pregnancies (n = 129) were matched by age, parity, farm location and month bred with mares diagnosed with a singleton pregnancy (n = 127). The effects of location of embryonic vesicles, mare age, reproductive status, parity, month of breeding, vesicle size and plasma progesterone concentration at pregnancy diagnosis on live foal rate were examined.
  
  
  RESULTS
  Position of embryonic vesicles at time of manual elimination, parity and month bred had no effect on live foal rate. Live foal rates in mares >9 years of age were lower (71.8%) than in all mares ≤9 years (87.1%; P<0.05). Mares >9 years of age that had a twin reduced lost more pregnancies (34.8%) than age-matched control mares (20.0%; P<0.005). Mean plasma progesterone concentration of twin-reduced mares was greater than in control mares when compared on the same day post ovulation. Plasma progesterone concentrations did not differ between mares that lost their pregnancy and those that delivered a live foal.
  
  
  CONCLUSIONS
  Mare age of >9 years is associated with decreased pregnancy rate after twin reduction.
  
  
  CONCLUSIONS
  Furthering the understanding of factors that affect live foal outcome following manual twin elimination in mares.
authors.affiliation: Rood and Riddle Equine Hospital, Kentucky, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Schnobrich
authors.forename: W T
authors.initials: WT
authors.lastname: Riddle
authors.forename: A J
authors.initials: AJ
authors.lastname: Stromberg
authors.forename: M M
authors.initials: MM
authors.lastname: LeBlanc
mesh_terms: D000034:Abortion, Veterinary; D000375:Aging; D000818:Animals; D016022:Case-Control Studies; D005260:Female; D006736:Horses / Q000502:physiology*; D036801:Parturition; D011247:Pregnancy; D011270:Pregnancy, Animal; D012189:Retrospective Studies
keywords: bilateral; elimination; horse; pregnancy; twin; unilateral