Variations in Grain Processing Influence Digestibility by Horses

Processing grain by crushing, grinding, or heating makes the starch in the grain more digestible for horses. Increased digestibility is desirable because starch that is not completely digested in the horse’s small intestine can flow into the hindgut, leading to rapid fermentation and digestive upsets.

Directly measuring starch digestibility in the horse’s small intestine is not easy to do, despite a number of methods that have been tried. Measurements of glycemic response after a meal have shown a positive correlation with the results of an in vitro small intestine starch digestibility assay. Based on this correlation, a comparison was made among the digestibility levels of barley and corn that had been processed by steam flaking or micronizing. The grains had been processed by five different manufacturers.

Digestibility varied for the two grains, both by processing method and also by manufacturer. The starch in micronized corn and barley was more fully digested (average 26% better) than when the grains were steam-rolled. When corn was micronized by two different manufacturers, percent of starch digested in 15 minutes was 83.6% for one manufacturer and 56.2% for another manufacturer. Micronizing of barley by three different manufacturers resulted in 59.5, 64.1, and 72.7% of starch being digested in 15 minutes.

What does this mean to the horse owner who is trying to select a feed that will be the best for her horse? She knows that processing generally improves digestibility of grain, but how much is enough? Is too much processing (starch may be digested very quickly, causing a glucose spike in the horse’s blood) worse than not enough processing (some undigested starch may flow into the hindgut)? And how can she find out the level of grain processing in a feed she is thinking of purchasing?

Because most horse owners have no way to determine exactly how the grain in a particular feed has been processed, they must trust that reputable feed manufacturers have designed their products to meet the nutritional needs of the horses for which the feeds will be used. This is a good reason to buy feed from a store or mill that consults with an equine nutritionist as feeds are formulated.

Tips for feed management: Base the horse’s diet around forage (grass and hay), adding grain only if the horse needs the extra energy for the work it is performing. Completely avoid using feeds designed for other animals such as cattle or sheep. Feed horses small meals (no more than five pounds (2.5kg) in a single meal). Make any feeding changes gradually over several days. Consult with an equine nutritionist if you have specific problems or questions about your feeding program.