title: Effect of twin birth calvings on milk production, reproductive performance, and survival of lactating cows.
abstract: OBJECTIVE
  To evaluate effect of twin birth calvings on milk production, reproductive performance, and survival of lactating cows.
  
  
  METHODS
  Retrospective observational cohort study.
  
  
  METHODS
  33,868 cows from 20 farms.
  
  
  METHODS
  Data on age at calving for primiparous cows and mature equivalent milk yield for multiparous cows, assistance at calving, stillbirths, twin births, gestation duration, pregnancy at the end of the data collection period, and culling-death for all cows were extracted from farm computer records and used for statistical analysis.
  
  
  RESULTS
  Prevalence of twin parturitions was 1.3% (159/12,050) and 6.5% (1,410/21,818) for primiparous and multiparous cows, respectively. Primiparous and multiparous cows with singletons produced more milk than cows with live twins or at least 1 dead twin (primiparous, 33.1 vs 31.9 vs 31.2; multiparous, 36.5 vs 35.7 vs 35.0). Multiparous cows with dead twins produced less milk than cows with live twins. Compared with dams with singleton birth, cows with twins were 0.78 times as likely to conceive and 1.42 times as likely to die or be culled. Cows with dead twins also had increased time to conception, compared with live twins.
  
  
  CONCLUSIONS
  Twin birth was associated with decreased survival, milk production, and reproductive performance. Having at least 1 dead twin was even more detrimental than having live twins and resulted in decreased milk production and reproductive performance of lactating cows.
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Rodrigo C
authors.initials: RC
authors.lastname: Bicalho
authors.forename: Soon Hon
authors.initials: SH
authors.lastname: Cheong
authors.forename: Klibs N
authors.initials: KN
authors.lastname: Galvão
authors.forename: Lorin D
authors.initials: LD
authors.lastname: Warnick
authors.forename: Charles L
authors.initials: CL
authors.lastname: Guard
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D005313:Fetal Death / Q000662:veterinary*; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000378:metabolism*; D010298:Parity; D011247:Pregnancy; D015995:Prevalence; D012098:Reproduction / Q000502:physiology*; D012189:Retrospective Studies; D016019:Survival Analysis; D014427:Twins