title: Event-time analysis of the effect of 60-day milk production on the parturition-to-conception interval in dairy cows.
abstract: OBJECTIVE
  To quantify the effect of early-lactation milk and milk fat production on time to conception.
  
  
  METHODS
  Event-time analysis (survival analysis).
  
  
  METHODS
  44,450 cows delivering calves between September 1985 and September 1986, from 6,227 Ayrshire dairy herds in 80 Finnish communities.
  
  
  METHODS
  Primiparous and multiparous cows were analyzed in separate Cox proportional hazards models. 60-day milk and milk fat production were categorized and regressed against days from parturition to conception for the period 56 to 120 postpartum days, controlling for season of parturition, parity, herd production, occurrence of 43 diseases, and community.
  
  
  RESULTS
  Multiparous cows producing above the 80th percentile for 60-day milk, but with milk fat production below the 75th percentile, were significantly more likely to conceive, compared with cows with lower production and compared with cows with similar milk production but with milk fat between the 75th and 97th percentiles. They were slightly more likely to conceive than cows with highest milk fat production, although not significantly so. Primiparous cows producing above the 80th percentile for 60-day milk with milk fat below the 75th percentile also had the highest conception probability. The highest producing primiparae had significantly lower conception probability than all others.
  
  
  CONCLUSIONS
  Controlling for disease occurrence, calving season, parity, herd production level, and community, there appeared to be an inverted U-shaped relation between 60-day production and conception probability.
  
  
  CONCLUSIONS
  Primiparous cows that are high producers may not be receiving the same careful management that high-producing multiparous cows receive.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Harman
authors.forename: Y T
authors.initials: YT
authors.lastname: Gröhn
authors.forename: H N
authors.initials: HN
authors.lastname: Erb
authors.forename: G
authors.initials: G
authors.lastname: Casella
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D003612:Dairying; D005260:Female; D005306:Fertilization / Q000502:physiology*; D007743:Labor, Obstetric / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D008055:Lipids / Q000032:analysis; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D010298:Parity / Q000502:physiology; D011247:Pregnancy; D011336:Probability; D016016:Proportional Hazards Models; D016019:Survival Analysis; D013997:Time Factors
chemical_list: D008055:Lipids