Forage-Only Diet Evaluated for Exercising Horses

Owners of top performance horses often run into a feed management dilemma. On one hand, their horses need a high level of energy that is most easily supplied by concentrate feeds that are made up mostly of grain. On the other hand, diets high in grain can lead to colic, hindgut acidosis, and other metabolic upsets.

Researchers from the Swedish University of Agricultural Sciences wanted to test the idea that an all-forage diet would improve aerobic energy metabolism, thus leading to greater efficiency in energy use. Using a forage-only diet (high-energy haylage fed at 2.2% of body weight) and a forage-and-concentrate diet (50% haylage and 50% soybean meal/wheat bran/oats), the researchers compared the difference in exercise performance of six Standardbred geldings in race training. The diets had the same caloric and protein content and were fortified with a mineral/vitamin supplement to meet NRC requirements.

Each horse ate one diet for the first 29-day study period and the other diet for the second period. The horses were trained during each period and performed an incremental exercise test on a treadmill on day 25 of each period. The horses were weighed and given a condition score, and muscle biopsies and blood samples were taken before, during, and after the treadmill test.

Results showed that V_La4 (the velocity when plasma lactate concentration is 4 mmol/l) tended to increase in horses eating the forage-only diet. This is an indication of better performance, according to the research report. Muscle glycogen, the first source of energy for exercising horses, was higher in horses eating the forage and concentrate diet. Blood analysis showed that pH was higher in horses on the forage-only diet, indicating a chance for this diet to counteract parts of the acidotic effect caused by strenuous exercise.

Researchers pointed out that the study did not show whether the forage-only diet decreased muscle glycogen storage capacity or the rate of glycogen synthesis. Overall fitness of the horse, level of exercise, and other factors could influence the suitability of a high-energy forage diet for performance horses.