Induction of Noninflammatory Pain in an Experimental Foot Lameness Model in Horses

The mechanism by which nonsteroidal anti-inflammatory drugs mitigate pain caused by a heart bar shoe (HBS) model of lameness is unknown. The purpose of this study was to determine if this HBS model of lameness induces inflammation in horses. Five healthy adult horses from a university teaching herd were enrolled. A custom HBS was applied to the left front foot of each horse, followed by induction of the American Association of Equine Practitioners Lameness Score of 4. Inflammatory markers including serum amyloid A (SAA) concentration, local venous tumor necrosis factor alpha and prostaglandin E2 (PGE2) concentrations, and foot temperature were measured before lameness induction and 1, 3, and 13 hours after lameness induction. Lameness induction using the HBS model did not significantly increase production of plasma SAA, tumor necrosis factor alpha, or PGE2 concentrations at measured time points. Immediately and 1 hour after lameness induction, dorsal coronary band temperatures were higher in the left front foot compared with the right front foot, but there was no difference at 3 or 13 hours. In conclusion, the HBS model did not induce inflammation as assessed by select inflammatory markers, suggesting that the HBS model induces mechanical rather than inflammatory pain. This should be considered when using the HBS model to assess analgesic drugs in horses.