Effect of training on plasma myeloperoxidase concentrations measured before and following intense exercise in Thoroughbred racehorses

Exercise in horses induces neutrophil degranulation and subsequent increases in plasma myeloperoxidase concentrations (MPO). It is not known whether this response is affected by training or the sampling time in relation to exercise. Our objective was to evaluate plasma MPO concentration at different time points in response to exercise in Thoroughbreds before and following high-intensity training and to evaluate relationships between plasma MPO concentration, physiological measurements and performance. Throughbred racehorses in active training and racing (n=26) performed an exercise test on a high-speed treadmill at least once at the beginning (first three months), middle (second three months) or end (last three months) of a nine month training period with training intensity (number of fast work sessions) collated for each period. Heart rate, speed and distance were recorded and venous blood collected before (T0), during and up to maximal speed (TVmax), 5 min (T5min) and 4 h (T4h) following exercise for me...