SURVIVAL ANALYSIS OF RISK-FACTORS ASSOCIATED WITH THE OCCURRENCE OF LAMENESS IN A MICHIGAN HORSE POPULATION

Objective-To evaluate the associations of operation and individual ani mal-level risk factors with occurrence of lameness in the Michigan hor se population. Sample Population-3,925 horses monitored from 138 rando mly selected Michigan operations for a total of 814,753 horse-days. Pr ocedure-All horses monitored < 60 days were eliminated from the source population. From the remaining horses, a prospective unmatched case-c ontrol study population was generated that included all cases and a ra ndom sample of noncases. Analysis of risk factors associated with occu rrence of lameness was conducted, using Cox's proportional hazards reg ression model. Results-Horses in larger operations, compared with hors es in the first operation size quartile, were associated with decrease d risk of lameness (2nd quartile [Q]: hazard ratio [HR] = 0.57; 95% co nfidence 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, stalli ons (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 us ed for breeding purposes only, those participating in exercise or perf ormance-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 increa sed risk of lameness. Conclusions-Comparison of these results with tho se conducted using multivariable logistic regression strengthens the a rgument that there is decreased risk of lameness for horses in larger operations and increased risk of lameness for active horses. Additiona lly, results of this analysis suggested that stallions and geldings ar e at increased risk of lameness, compared with mares. Clinical Relevan ce-Lameness prevention strategies in the horse industry should focus p rincipally on horses participating in exercise or performance-related activities, including racing and showing, on male horses, and on horse s stabled in smaller operations.