Effects of mild forelimb lameness on exercise performance

Mild lameness is considered a performance-limiting problem that may escape detection until it worsens, and is considered the primary reason for reduced racing performance. The kinematics changes associated with a lame horse at the trot have been demonstrated previously, but the metabolic cost of these alterations in their gait have not been demonstrated. Six fit Thoroughbred horses with an established VO2max participated in 4 trials using a randomised cross-over design study, separated by 10-14 days. The horses were tested with one of 4 trial conditions: lead forelimb lameness (LL); off-lead forelimb lameness (OL); bilateral forelimb lameness (BL) or no lameness (NL). Lameness was induced by sole pressure from a modified shoe that resulted in a consistent slight head nod at a trot in a straight line while jogging in hand. Lameness was adjusted to provide a lameness that would be quantified as a 1-2/5 on the grading system recommended by the AAEP. Each trial consisted of 4 different levels of exercise intensity at speeds equivalent to 30, 60, 80 and 110% of an individual's speed required to elicit VO2max. Stride parameters, oxygen consumption (VO2), carbon dioxide production (VCO2), electrolytes, plasma lactate, glucose and PCV/TP were measured prior to exercise, at each exercise level and after exercise. A multiway ANOVA with repeated measures was utilised to examine possible effects of individual horse, lameness, and exercise intensity on measured parameters. Significance was set at alpha = 0.05. For horses exercising at the maximum intensity, VO2 was significantly lower for both of the single-leg lamenesses (LL or OL) when compared to NL or BL (mean +/- s.e. 165.6 +/- 2.5, 164.7 +/- 3.0, 175.8 +/- 2.4 and 170.9 +/- 2.1 ml O2/min/kg bwt, respectively). Blood lactate concentrations were not significantly different among the treatment groups. However, lactate accumulation rates computed as the change with time in lactate concentration at the highest exercise intensity were significantly higher for LL and OL than for NL and BL (7.8 +/- 03, 83 +/- 0.2, 4.1 +/- 0.2 and 4.7 +/- 0.3 mmol/min, respectively). Exercise intensity had significant effects on all of the measured parameters, but there were no other significant differences due to treatment. These results suggest that metabolic energy transduction is affected by even mild unilateral forelimb lamenesses.