Indicators of exhaustion and stress markers in endurance horses

Abstract

Intensive physical activity leads to a variety of changes and adaptations, which may influence health and racing performance of horses. Key changes in the body occur due to the loss of fluids and electrolytes, primarily through sweating and ventilation, leading to accumulation of harmful metabolic products and consequential cell damage. These changes lead to the onset of symptoms of fatigue, exhaustion and stress, with prolonged delayed reaction that can be monitored in post exercising period (10, 30). Intensity of fatigue, exhaustion and stress depend on the amount of workload, environmental conditions under which the work is done and level of fitness and soundness of the horse. Beside the physical fatigue and accumulation of harmful metabolites, external conditions – i.e. temperature, humidity, wind, altitude and track quality (hard, heavy, slippery, deep, steep) – have a significant role in building fatigue due to the large distances that endurance horses have to cover. Sweating, especially during hot, humid days can lead to dehydration and electrolyte disbalance and due to the development of metabolic syndrome and disqualification, and in some cases, a horse can even collapse before reaching the finish (3, 4, 17). Subclinical injuries of locomotory apparatus can lead to lameness in late phases of the competition, while incorrect shoeing, respiratory and cardiovascular problems, also influence the outcome of the race and horses with any of these conditions usually find it harder to tolerate ambiental conditions (3, 4, 19). Physical activity can lead to visible fatigue, depression, difficult breathing, excessive sweating and/or lameness. Physical activity also induces changes of several hematological and biochemical parameters. Inadequate muscle perfusion can lead to anaerobic glucose metabolism and the building up of acid metabolites, predominantly lactic acid, lowering pH and the depletion of buffering capacities of body fluids (5, 21, 23). Horses loose large amounts of fluids through sweating, which causes an increase in total protein and albumin concentration, development of hemoconcentration and an increase in packed cell Indicators of exhaustion and stress markers in endurance horses