Carbohydrates, including starches, sugars, and fiber, provide horses with the energy they need to meet their daily requirements. But what type of carbs should you be feeding? High-starch diets, for instance, can increase the risk of metabolic disease, while high-fiber diets might better support horses' nutritional health.

Recently, Danish and Norwegian researchers studied how high-fiber feeds affect horses' nutrient digestibility, feed passage rate, and nitrogen and water balance.

The research team fed four Norwegian Trotter geldings fitted with a cecal cannula (a tube researchers could collect samples from) four energy-equivalent diets. These diets contained enough digestible energy and protein to sustain a 550-kilogram (1,200-pound) horse in light to moderate exercise yet had varying carbohydrate fractions. The diets included:

  • Hay only;

  • 85% hay and 15% soaked sugar beet pulp (SBP);

  • 68% hay and 32% pelleted barley; and

  • 68% hay, 26% pelleted barley, and 6% SBP.

To measure each feed's total mean retention time (TMRT), the team added a nondigestable marker called ytterbium to the horses' hay.

“The marker fed to the horse will pass undigested through the gastrointestinal tract and be excreted in feces,” explained lead researcher Rasmus Bovbjerg Jensen, PhD, of the University of Copenhagen Department of Veterinary Clinical and Animal Sciences. “By taking fecal samples and analyzing them for ytterbium, it is possible to … measure how long the feedstuffs are retained in the gastrointestinal tract

After an 18-day adaptation period to each diet, the researchers collected data for 10 days.

Key study findings included:

  • The SBP diet had the highest fiber digestibility of the four options;

  • The hay-only diet resulted in higher water intake than the other diets, but the team found that diet had no effect on water balance (on nitrogen balance);

  • The hay and SBP diets' TMRT was five hours shorter than that of the diets including barley.

Regarding the lower TMRT of the hay and SBP diets, Jensen said, “Is this good or bad? We do not know. But combining different techniques like in this study it helps us to understand how different diets are digested in the gastrointestinal tract of the horses.”

The study, "The effect of dietary carbohydrate composition on apparent total tract digestibility, feed mean retention time, nitrogen and water balance in horses," will appear in an upcoming issue of Animal