The Adaptive Equine Stomach

A study at the Island Whirl Equine Colic Research Laboratory at the University of Florida has determined that the horse's stomach can adapt to meals of various sizes and compositions, giving researchers a better understanding of how the normal stomach works. Following other studies, this could provide insight into the relationship between feeding practices and risk for development of colic. The study was published in the Sept. 8, 2002, issue of the American Journal of Veterinary Research.

According to Alfred Merritt, DVM, MS, Appleton Professor in Equine Studies, and director of the colic laboratory, "It was the first pass at trying to see how the equine stomach responds to taking in a meal," he said. "Does it relax? Does it have some variable response due to meal composition?"

Using six adult horses, researchers assessed the gastric tone in the proximal (upper) portion of the stomach during and after ingestion of each of four rations, which were 0.5 grams of grain per kilogram of body weight, 1.0 g of grain/kg, 0.5 g of hay/kg, and 1.0 g of hay/kg. The proximal portion of the stomach acts as a reservoir for food by initially relaxing, followed later by increased pressure changes that promote emptying of the digested food from the stomach.

A barostat bag, which is made of polyester, was inserted into the proximal portion of the stomach, and changes in the air volume in the bag gave clues about the tone (amount of relaxation) of the gastric wall. A baseline volume was recorded, then each horse consumed one of the four meals. The bag volume was recorded for 90 minutes after feeding. An initial receptive relaxation of the stomach was observed in response to all four meals, which was expected according to how other species' stomachs react to food. Both hay meals and the 1 g of grain/kg meal caused receptive relaxation, followed shortly by a second, less profound relaxation, called adaptive relaxation or accommodation, that was sustained throughout the rest of the 90-minute post-feeding period. The larger hay meal caused the horse's stomach to relax more and for longer due to increased time for consumption, which might have also stimulated the gastrointestinal tract to work longer. The small grain meal caused less relaxation than the other meals, and the first phase melded into the second phase. These results signify that the size of the meal affected the magnitude of relaxation of the stomach. Merritt comments that it is more natural for a horse to eat small amounts more frequently throughout the day rather than larger meals.

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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