The effect of roughage source on exercise performance and metabolism in thoroughbred horses

The effects of roughage source on metabolism and exercise capacity were investigated using 6, previously conditioned, mature thoroughbred horses in a cross-over experiment. The horses were assigned to either non-alfalfa or alfalfa roughage diets which were isocaloric. The diets were fed for 2 weeks, after which the horses were exercise tested and then fed the alternate diet. Horses were exercised on a high-speed treadmill using a rapid incremental test. Arterial blood samples were collected for blood gas analysis and acid base measurements and venous blood samples for lactate and red blood cell potassium analysis. Mixed expired gas samples were collected for measurement of oxygen uptake, carbon dioxide production and respiratory exchange ratio. Heart rate was measured by telemetry ECG and respiratory frequency by observation. When the 2 diets were compared there were no significant differences in treadmill exercise capacity nor in any of the metabolic or cardiorespiratory measurements made before, during or after the exercise period. We concluded that roughage source has no effect on cardiorespiratory and metabolic function during or after exercise, and does not affect endurance performance during a treadmill exercise test.