Reasons for performing study: Endurance races are the competition with the biggest metabolic demands for the sport horse. During races, some horses show homeostasis alterations, having repercussions in diverse biochemical parameters and negative consequences on performance and health.
Objectives: To evaluate the utility of biochemical analysis in the early diagnosis of metabolic stress and to determine cut-off values of biochemical parameters to assist in the prevention of metabolic alterations in endurance horses.
Methods: This study involved 36 CEI races and 283 horses (41 eliminated because of metabolic disturbances). Blood samples were taken before competition, after the vet-gates and after finishing the race or veterinary disqualification. Packed cell volume (PCV), activities of CK, AST and LDH, and concentrations of total plasma proteins (PP), urea, creatinine (Cr), uric acid (UA) and plasma lactate were determined. Successful horses were compared with horses eliminated due to metabolic conditions in the values obtained in the phase prior to being removed from the competition. Factors associated with metabolic elimination were further analysed using multiple logistic regression analysis. Dichotomisation for each variable was made using the receiver-operating characteristic curve to enter into the model.
Results: PCV>52%, PP>82 g/l, standardised Cr>30 mg/l 100 km, UA>72 mg/l, standardised CK>12.6 ui/l km and standardised AST>6.2 ui/l km were associated with the development of metabolic alterations. Of the horses with an imbalance between PCV and PP, 30% had metabolic elimination in the following phases. Muscle enzymes and Cr were directly related to the distance covered.
Conclusions: Selected biochemical markers are evident in some endurance horses before their elimination. However, most horses developed metabolic disturbances without any important alterations in the variables determined in this study.
Potential relevance: Analysis of selected plasma biochemical parameters could be useful in the prevention and early diagnosis of metabolic stress in endurance horses.