Supplementing Enzymes in the Equine Diet

Researchers have discovered that supplementing enzymes could help digestion of starch in the equine small intestine. "With dietary enzyme supplementation and enhanced small intestinal starch digestion, the feeding of cereal grains to horses will become a more efficient and safer practice than it has been in the past," said Nerida Richards, PhD, of the School of Rural Science and Agriculture at the University of New England in Armidale, New South Wales, Australia. Richards presented "Starch Digestion in the Equine Small Intestine: Is There a Role for Supplemental Enzymes?" at the sixth annual equine school at the Alltech Symposium in Lexington, Ky.

As a natural grazer, consuming grain is not the most natural thing for a horse. Despite this, grains have been incorporated into the diet as a source of energy so that a horse can meet the energy demands of performance. Ideally, starch should be digested by enzymes in the small intestine, with as small an amount as possible being passed into the hindgut for continued digestion. Any amount that does pass to the hindgut for digestion could cause problems for the horse.

Starch in the hindgut undergoes fermentation, yielding 35-40% less metabolizable energy than if it is digested in the small intestine, said Richards. But that isn’t the worst problem. This hindgut digestion causes radical changes to the constitution of hindgut flora and a subsequent increase in volatile fatty acid and lactic acid concentrations in the cecum and colon. This increased acidity causes hindgut lactic acidosis, which has been associated with the onset of laminitis, endotoxemia, metabolic acidosis, and behavioral problems such as wood chewing and cribbing, explained Richards.

Improving small intestine digestion could help prevent these problems. However, the equine small intestine is not designed for digestion of large amounts of starch. Feeding processed grains can help. Studies have shown that triticale (a hybrid of wheat and rye) and oats are the most digestible grains, followed by barley, white rice, and corn. Even with these grains, barriers such as the seed coat, starch granule and biochemical structure, endosperm cell wall structure, and protein matrix structures stand in the way of digestion. During processing, heat, moisture, and pressure can disrupt starch granule structure, destroy crystalline starch formations, increase the water solubility of starch, and physically expose starch to digestive enzymes, said Richards.

Further studies into starch digestion by horses has determined that in vivo (in the living horse) digestibility did not appear to respond to grain processing to the same extent as observed in vitro (in the laboratory). It has also been observed that starch digestion will vary from horse to horse. “Physical and physiological attributes of individual horses are limiting the extent of starch digestion in the small intestine, with a low glycemic response indicating a limited ability to digest starch,” said Richards.

So, why can’t horses digest starch effectively in the small intestine? Further research into this issue has discovered that concentrations of starch-digesting enzymes--especially alpha-amylase--in the equine small intestine are low and vary widely between horses. Richards also pointed out that not all alpha-amylases have the same capacity to digest starch and that equine alpha-amylase appears to have a limited capacity for starch digestion.

Richards and colleagues hypothesized that equine alpha-amylase is inferior to the bacteria Bacillus licheniformis alpha-amylase and that supplemention with B. licheniformis alpha-amylase by itself or in combination with amyloglucosidase (AMG, another starch digesting enzyme found in the small intestine) could improve starch digestion in the horse. In their study, horses were fed a processed grain diet with four different combinations of enzyme supplementation. These were a control diet (no enzyme added), a diet with B. licheniformis alpha-amylase, a diet with AMG, and a diet with B. licheniformis alpha-amylase and AMG combined.

It was found that supplementation with the alpha-amylase and AMG resulted in the most efficient starch digestion, followed by supplementation with only the alpha-amylase enzyme. The addition of AMG alone made no difference. These results allowed Richards to hypothesize that a deficiency and/or a low activity of alpha-amylase is the major limiting factor to starch digestion in the equine small intestine. The fact that the combination with AMG helped digestion indicates that extra AMG might be necessary when alpha-amylase is added to the diet.

Richards listed four benefits of enzyme supplementation. These were:
• Improved feed efficiency due to increased starch digestion in the small intestine;
• A decreased incidence of hindgut starch fermentation, resulting in a decreased risk of hindgut acidosis;
• A decrease in the occurrence of diseases associated with hindgut acidosis; and
• A decrease in adverse behaviors associated with hindgut acidosis.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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