title: Survival analysis of risk factors associated with the occurrence of lameness in a Michigan horse population.
abstract: OBJECTIVE
  To evaluate the associations of operation and individual animal-level risk factors with occurrence of lameness in the Michigan horse population.
  
  
  METHODS
  3,925 horses monitored from 138 randomly selected Michigan operations for a total of 814,753 horse-days.
  
  
  METHODS
  All horses monitored < 60 days were eliminated from the source population. From the remaining horses, a prospective unmatched case-control study population was generated that included all cases and a random sample of noncases. Analysis of risk factors associated with occurrence of lameness was conducted, using Cox's proportional hazards regression model.
  
  
  RESULTS
  Horses in larger operations, compared with horses in the first operation size quartile, were associated with decreased risk of lameness (2nd quartile [Q]: hazard ratio [HR] = 0.57; 95% confidence interval [CI]: 0.36, 0.91; 3rd Q: HR = 0.74; 95% CI: 0.49, 1.13; 4th Q: HR = 0.46; 95% CI: 0.28, 0.76). Compared with mares, stallions (HR = 1.90; 95% CI: 1.17, 3.07) and geldings (HR = 1.46; 95% CI: 1.02, 2.09) were at increased risk of lameness. Compared with horses used for breeding purposes only, those participating in exercise or performance-related activities including racing (HR = 4.70; 95% CI: 1.70, 13.03) and showing (HR = 2.80; 95% CI: 1.07, 7.28) also were at increased risk of lameness.
  
  
  CONCLUSIONS
  Comparison of these results with those conducted using multivariable logistic regression strengthens the argument that there is decreased risk of lameness for horses in larger operations and increased risk of lameness for active horses. Additionally, results of this analysis suggested that stallions and geldings are at increased risk of lameness, compared with mares.
  
  
  CONCLUSIONS
  Lameness prevention strategies in the horse industry should focus principally on horses participating in exercise or performance-related activities, including racing and showing, on male horses, and on horses stabled in smaller operations.
authors.affiliation: Population Medicine Center, College of Veterinary Medicine, East Lansing, MI, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Ross
authors.forename: J B
authors.initials: JB
authors.lastname: Kaneene
authors.forename: J C
authors.initials: JC
authors.lastname: Gardiner
mesh_terms: D000367:Age Factors; D000818:Animals; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology*; D006736:Horses; D007794:Lameness, Animal / Q000453:epidemiology*; D008297:Male; D008824:Michigan / Q000453:epidemiology; D009919:Orchiectomy; D010805:Physical Conditioning, Animal; D015995:Prevalence; D016016:Proportional Hazards Models; D012307:Risk Factors; D012727:Sex Characteristics; D013045:Species Specificity; D016019:Survival Analysis