Grain Meals Alter Hindgut pH in Racehorses

Australian researchers* investigated the type and amount of cereal grains fed to Thoroughbred horses in race training and the impact of these feeds on the equine hindgut.

To gather information about feeding practices, researchers interviewed 72 Thoroughbred trainers and collected samples of grain and chaff fed to horses in training. Grains were analyzed for in vitro starch digestibility, and fecal samples were analyzed for pH, dry matter, starch content, nitrogen content, and concentrations of lactic and volatile fatty acids.

Results showed that the most common feeds used by trainers were oats (81%), corn (74%), and commercial premixed products (73.6%). About one-third of the trainers fed barley. Most grains were fed whole, with only 20% of grains being processed before feeding. On average, horses were fed 7.3 kg (16 lb) of grain/day. Mean fecal pH was 6.5, and the lowest reading was 5.5. A pH level lower than 6.2 was found in 27% of samples, indicating a status below the optimum pH for cellulolytic and lactate-utilizing bacteria. The relation between fecal pH and propionate concentrations suggested that lower pH values are due to the fermentation of starch by amylolytic bacteria.

The amounts of oats, commercial feeds, total grain, and chaff in the equine diets were not related to the concentration of organic acids in the feces of horses in this study. However, the amount of dietary corn fed, which is digested less efficiently than oats in the small intestine, related positively to total fecal acid concentration.

Results showed that grain feeding practices resulted in some degree of hindgut starch fermentation and acidosis for more than a quarter of horses in this study. These digestive upsets could negatively impact athletic performance and lead to conditions like laminitis. Selecting grains with superior small intestinal starch digestibility characteristics or alternative low-starch, high-energy feeds could help trainers minimize these problems.

To counteract the drop in pH that characterizes hindgut acidosis, horse owners can turn to a time-released hindgut buffer like EquiShure from Kentucky Equine Research. Encapsulation technology utilized in EquiShure ensures targeted release of buffering agents directly in the hindgut.

*Full text of “The effect of current grain feeding practices on hindgut starch fermentation and acidosis in the Australian racing Thoroughbred,” presented at the 2006 Australian Equine Science Symposium.