O|3 Minute Tip of the Week

Digestibility and Rate of Passage

Meredith Kahn, MS

Equine Nutrition Consultant

O|3Animal Health, LLC.

Various factors exist that affect digestibility and rate of passage through the equine digestive system. The digestibility of forage (hay) versus grain, for example, is something that can be examined closely. On a general note, grains, or non-structural carbohydrates, are more highly digestible than forages, which are mainly composed of structural carbohydrate. In fact, the overall rate of digestibility improves as the system relies less on fermentation of structural carbohydrate.

Different grain types are also more or less digestible than their counterparts. Cold or hot feed processing, for example, has numerous influences on the digestibility of grain. Reduced particle size is a form of cold processing that increases digestibility through the system. Cold cracking and grinding of grain expands the surface area with which digestive enzymes have to work. Hot steam flaking and pelleting increase digestibility by adding an appetizing toasted flavor that horses tend to prefer over raw grains. Other flavor additives work to enhance digestibility by increasing palatability or the amount of grain ingested.

In addition, assorted feedstuffs move at a different rate of passage through the system. A number of factors work to change the mean retention time (MRT): the time spent in the entire system or, broken down more specifically, the time spent in a single organ of the system. While reducing the particle size generally increases digestibility, smaller particles also move more quickly through the digestive track, which can decrease overall digestibility. Therefore, to ensure optimal digestibility, we must find the correct balance between reducing particle size to increase surface area and maintaining a slow enough rate of passage to give enzymes adequate time to work. This is especially true for fermentation, which requires ample time for completion.

The amount ingested also has an effect on rate of passage. Increased amounts of ingested grain, for example, speed up the rate at which it moves through the system. This in turn will actually decrease digestibility, as digestive enzymes in the small intestines require time to break down non-structural carbohydrate. Undigested non-structural carbohydrate in the small intestine continues on to the large intestine, where it is fermented and absorbed as a completely different product. This can often cause digestive upset such as colic, when horses eat too much grain in one sitting. Therefore, it is important to consider feeding many small meals throughout the day, especially when feeding a horse that is being offered any sort of additional energy through grain supplementation.

Stay tuned for a discussion on carbohydrates in the next O|3 Minute Tip of the Week!

FYI: MRT in the stomach may be increased by fat inclusion in the diet. Adding an oil like Equine Omega Complete to the diet may help provide a slow and steady supply of glucose throughout the day. Decreased gastric emptying may help counteract overwhelming of the small intestines, preventing possible digestive upset due to grain supplementation.

Meredith Kahn and Gatsby

About the Author: Growing up in the San Francisco Bay Area, Meredith developed an immediate passion for horses when she began taking riding lessons at the age of five. She has been riding and showing Hunter Jumpers as a member of KMC Farm, currently located at Sonoma Horse Park, since 2003. After graduating from The University of San Francisco with a Bachelor’s degree in Biology, Meredith decided to further her education in a field where she could concentrate on helping horses. In 2014 she earned her Master’s degree in Animal Science, with an emphasis in equine nutrition, from Texas A&M University. Now back in California, as our Equine Nutrition Consultant, Meredith uses her education and extensive background as an equestrian to advise and educate clients about our products and assist with their horse’s nutritional needs. Meredith is excited to be a part of the wonderful team at O|3 Animal Health.

Questions for Meredith? m.kahn@o3animalhealth.com