Validation of a Reversible Lameness Model and the Assessment of a Topically Applied Nonsteroidal Anti-Inflammatory Drug

The objective of this study was to validate and use a model of reversible foot lameness in the horse. The model used both forelimb hooves fitted with a clamp. After force platform baseline measurements, one clamp was tightened to induce an asymmetry index (ASI) between 25% and 30% and left in place for 120 hours. Serial force platform measurements were obtained. After 120 hours, the clamp was released, and force platform data were recorded until the horse returned to soundness. The procedure was repeated on the opposite forelimb. To use the model, the same procedure was performed in another group of horses with one limb treated with topical diclofenac at 12-hour intervals beginning when the initial ASI was between 25% and 30% and continued for 120 hours. The response was evaluated for each outcome variable using linear mixed models. Time (duration of clamp being tight), limb (left or right), and clamping order (first or second foot) were fixed effects, whereas horse was a random effect. A similar analysis was completed with the additional variable (diclofenac treatment) for the model utilization data. For model validation, the only significant force plate data variable was time, which is consistent with model design. For model utilization, there was a significant effect of time and a significant decrease in the ASI associated with topical diclofenac. The model created a consistent lameness that will provide a mechanism to compare treatments for pain and lameness. Topical diclofenac applied twice daily decreased the lameness associated with the model.