Physiological and blood biochemical variables in horses exercising on a treadmill submerged in water

The blood lactate concentration (LA) and heart rate (HR) of 10 horses exercising in water on a treadmill were examined. With the water at 10 and 50% of the withers height (WH), the blood LA increased up to mean values around 1.9 mm during the standardized exercise test (SET) until after step 3 of 5 (each step lasted 5 min, speed increasing step by step). Thereafter, blood LA of horses remained constant, while with the water at 80% of WH, the blood LA decreased from the mean peak of 2.16 ± 0.62 mm after the 4th step. The HR of the horses increased to 132 ± 14 beats/min until the 3rd step of SET with the water at 10% of WH, up to the 2nd step with the water at 50% (134 ± 10 beats/min) and up to the 1st step only with the water at 80% of WH (134 ± 10 beats/min). In another SET, horses were exercised five times for 5 min at the maximal attainable speed of 5.5 m/s in water at 20% of the withers height in step 1, 35% in step 2, 49% in step 3, 63% in step 4 and 77% in step 5. On using this SET, blood LA increased to 1.91 ± 0.25 mm until after the 2nd step and decreased after the 3rd step. The HR increased between before commencing SET and the 1st step (143 ± 13 beats/min) and remained constant thereafter. In conclusion, increasing water height and speed of exercise does not augment continuously blood LA and HR of horses exercising in water treadmills.