Causes of Horse Ulcers
Several factors contribute to the development of ulcers, including stress, high carbohydrate diets, being fed twice a day instead of grazing, and physical activity:
Since horses evolved with a nervous system that is highly responsive to stress, they are exceptionally sensitive to the stress hormone, cortisol. It's the interaction of cortisol with the vagus nerve, which controls digestion, that causes ulcers. Circumstances that contribute to ulcer development are those that increase cortisol: shipping, performing, changing diets, and changing schedules. Thus, horses in training that are shipped to events are prone to ulcers even though they enjoy performing and may appear unstressed.
High Carbohydrate Diets
High carbohydrate diets can predispose horses to ulcers and acid reflux. Carbohydrates release volatile fatty acids that enter stomach cells and encourage ulcer development.
Being Fed Twice a Day Rather Than Grazing
Horses fed twice a day rather than allowed to graze on pasture are prone to ulcers. This is because grazing 8-16 hours a day stimulates constant saliva flow. Saliva has a basic pH and is the opposite of the stomach acidic pH. A constant flow of saliva neutralizes stomach acid. Horses evolved eating almost continuously, so their stomachs evolved to release acid steadily during the day. When horses are fed only twice a day, gastric acids are produced continuously, but there is insufficient saliva to buffer the stomach contents and keep the lining of the stomach ulcer free.
Horses undergoing physical activity, such as racing, may develop ulcers because exercise causes abdominal muscles to contract. Abdominal contractions force bile and acidic contents from the intestine back into the stomach where they irritate the stomach lining and cause ulcers.