Survival analysis of risk factors associated with the occurrence of lameness in a Michigan horse population

Whitney A. Ross From the Population Medicine Center, College of Veterinary Medicine (Ross, Kaneene) and the Biostatistics Unit, Department of Epidemiology (Gardiner), Michigan State University, East Lansing, MI 48824-1314.

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John B. Kaneene From the Population Medicine Center, College of Veterinary Medicine (Ross, Kaneene) and the Biostatistics Unit, Department of Epidemiology (Gardiner), Michigan State University, East Lansing, MI 48824-1314.

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Joseph C. Gardiner From the Population Medicine Center, College of Veterinary Medicine (Ross, Kaneene) and the Biostatistics Unit, Department of Epidemiology (Gardiner), Michigan State University, East Lansing, MI 48824-1314.

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SUMMARY

Objective

To evaluate the associations of operation and individual animal-level risk factors with occurrence of lameness in the Michigan horse population.

Sample Population

3,925 horses monitored from 138 randomly selected Michigan operations for a total of 814,753 horse-days.

Procedure

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 [Qj: 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.

Clinical Relevance

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. (Am J Vet Res 1998;59:23–29)

SUMMARY

Objective

To evaluate the associations of operation and individual animal-level risk factors with occurrence of lameness in the Michigan horse population.

Sample Population

3,925 horses monitored from 138 randomly selected Michigan operations for a total of 814,753 horse-days.

Procedure

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 [Qj: 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.

Clinical Relevance

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. (Am J Vet Res 1998;59:23–29)

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