Metabolic Response of Arabian Horses to Endurance Racing

Unlike Thoroughbreds that commonly compete in races of a mile or less in length, horses trained for endurance competition may be asked to cover much longer distances at a slower pace. Short, fast races and longer, slower competitions cause fatigue in somewhat different ways. Fatigue in endurance horses results from heat production, loss of electrolytes and water, lactic acid production, metabolic alkalosis, and other factors.

Uric acid, a waste product of exercise and a biomarker of oxidative stress, has both pro-oxidant and antioxidant properties. In endurance horses, its pro-oxidant properties are stronger, and uric acid builds up quickly when energy balance is challenged by intense exercise. A study led by veterinary researchers from Malaysia and Nigeria was designed to investigate the changes in uric acid, white blood cells, plasma biochemical parameters, and heart rate in endurance horses.

Thirty Arabian horses were used in the study. The horses entered an 80-km race, with 10 completing the race and 20 being eliminated before the finish. The horses were examined before, during, and after the race and heart rate, gut motility, and other signs were recorded. Blood samples were drawn, white blood cells were counted, and uric acid and other levels were determined.

Most of the biochemical parameters measured were significantly elevated though heart rates were within the normal range. After the race, horses that finished had significantly lower levels of uric acid, lactate, plasma protein, and creatine kinase than horses that were eliminated. Significant positive correlations were found between pre-race and post-race uric acid levels and white blood cells, lactate, plasma protein, total protein, heart rate, creatine kinase, and other parameters. This was true for horses that finished and also in eliminated horses.

The researchers suggested that further studies would help to clarify whether uric acid level could be used to evaluate performance and health status in endurance horses during training and competition.