title: Association of sex of fetus, sire, month of conception, or year of foaling with duration of gestation in standardbred mares.
abstract: OBJECTIVE
  To determine whether sex of fetus, sire, month of conception, or year of foaling was associated with duration of gestation in mares.
  
  
  METHODS
  Epidemiologic retrospective cohort study.
  
  
  METHODS
  500 foalings for 296 Standardbred mares.
  
  
  METHODS
  Data for reproductive events from 1986 to 1992 were analyzed. Analyses were conducted to determine whether duration of gestation was associated with sex of fetus, sire, month of conception, or year of foaling.
  
  
  RESULTS
  Mean duration of gestation was 343.3 days and was significantly greater for colt fetuses (344.4 days) than for filly fetuses (342.2 days). Sire was associated with duration of gestation; gestation after mating with certain sires was consistently less than 340 days in duration, whereas duration after mating with other sires was consistently more than 350 days. Duration of gestation was associated with month of conception, decreasing by about 2.5 d/mo for mares conceiving later during the breeding season.
  
  
  CONCLUSIONS
  Duration of gestation is affected by mating to specific sires and by month of conception. Stallions associated with exceptionally prolonged gestations might be used to breed mares early in the breeding season, whereas stallions associated with shorter gestations might be desirable for mares bred later in the breeding season. Preparations for impending parturition should be more effective and efficient with improved information on expected date of parturition.
authors.affiliation: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing 48824-1314, USA.
authors.forename: J V
authors.initials: JV
authors.lastname: Marteniuk
authors.forename: C L
authors.initials: CL
authors.lastname: Carleton
authors.forename: J W
authors.initials: JW
authors.lastname: Lloyd
authors.forename: M E
authors.initials: ME
authors.lastname: Shea
mesh_terms: D000818:Animals; D005260:Female; D005306:Fertilization / Q000502:physiology; D005865:Gestational Age; D006736:Horses / Q000502:physiology*; D008297:Male; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D012621:Seasons; D012737:Sex Factors