Hemogasometry of eventing horses before and after intense exercise on a high speed treadmill

Abstract

The aim of this study was to evaluate the hemogasometric changes in horses and their metabolic acid–base status after intense exercise. The study was carried out at the Equine Performance Evaluation Laboratory at the Brazilian Army Cavalry School, Rio de Janeiro. Fourteen Brazilian Sport Horses, between 4 and 6 years old, at the beginning of Eventing training were used. The incremental speed test on a treadmill consisted of a 10-min warm-up and then galloping from 5.0m/s with speed increases every 1min until 8m/s, after which the horses galloped until they were unable to maintain this latter speed, indicating the end of the test. Recovery was carried out at walking speed. Hemogasometric samples were collected 6h before the test began, i.e. at rest, and immediately after the exercise test, and analyzed on a portable i-Stat (Roche®) device. The mean value of HCO3− after the test was lower (P<0.05) compared to the mean value before the test, 21.0±2.6 and 28.6±1.5mmol/L, respectively. The pH value was also lower after the incremental speed test, with a mean value of 7.26±0.06, compared to the mean value before the test, of 7.40±0.03 (P<0.05). The lactate concentration increased from 0.4±0.1 at rest to 11.8±5.5mmol /L at 8m/s (P<0.05) at the end of the test. The mean partial pressure values of O2 and CO2 before exercise were 33.0±2.8 and 46.2±3.7mmHg, respectively. At the end of the test, there was an increase in pO2 to 41.0±5.9mmHg due to the high oxygen uptake. However, the mean value of pCO2, at 47.8±2.5mmHg, remained the same suggesting a compensatory hyperventilation when the test was stopped due to fatigue and the samples were collected. The values of oxygen saturation did not differ before or after exercise (P>0.05), 63.0±6.2 and 58.0±10.3%, respectively, even for the horses that had an increased body temperature and a drop in pH after the exercise. The effort during the tests reduced blood pH and HCO3−, without reaching metabolic acidosis, which showed that the horses stopped galloping before any marked changes in the hemogasometric took place. The values of pCO2 did not change, probably due to hyperventilation at the end of the test.