Physiological Parameters of Endurance Horses Pre- Compared to Post-Race, Correlated with Performance: A Two Race Study from Scandinavia

Few studies have investigated the physiological parameters of endurance horses in Scandinavia. Hence, this two race study has focused on the effects of endurance racing in terms of equine clinicopathological blood parameters, heart score, and fluid use. Race A involved 15 horses (120？km). Two pre- and one post-race blood samples were taken, body condition score was assessed in triplicate pre-race, and an ECG was used to determine heart score. Race B involved 16 horses (65–120？km). One pre- and two post-race blood samples were taken. For both races, horse data as well as fluid intake estimates and cooling water were noted. Race A showed that blood haematocrit, albumin, sodium, and triglycerides increased significantly with endurance racing, whilst chloride, glucose, iron, and potassium decreased significantly. In race B, blood creatinine, cholesterol, and inorganic phosphate continued to increase significantly during the first post-race sampling period compared to pre-race levels, whilst iron, which decreased significantly during the race, increased significantly over the two post-race sampling periods. It is concluded that whilst no correlation between heart score and speed was observed, a significant correlation exists between experience and changes in blood parameters with endurance racing and between fluid intake and average speed. 1. Introduction The effects of prolonged submaximal exercise on a number of physiological parameters in the horse have been reported. Submaximal work, such as endurance racing, results in evaporative heat loss, with a loss of 10–15 liters per hour, primarily as sweat [1]. Indeed, net fluid deficits of 20 to 40 liters after rides of more than 80 kilometers are common [2–4]. Hence, weight losses of 4–7% of body weight in connection with endurance racing have been found in several studies [2, 5, 6] and are primarily due to uncorrected sweat loss. As a consequence, performance is affected as a result of a 3% level of dehydration [7]. Dehydration affects the capacity for evaporative heat loss, leading to elevated core temperatures in horses, despite an unaltered sweat production [8]. Also of importance is the fact that horses secrete hypertonic sweat [9, 10] with a mean electrolyte concentration of 159？mmol/L sodium, 32？mmol/L potassium, and 165？mmol/L chloride, which can lead to a substantial loss of electrolytes as well as water [2, 9]. In support of which, several studies have shown a post-race decrease in plasma concentrations of sodium, potassium, chloride, and calcium in horses [11–13], although one study has reported an