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Equine Gastric Acid - 12 Facts You May Not Know

Gastric acid is produced continuously by horses, donkeys and mules, whether there is food in the stomach or not.  Following are 12 facts about gastric acid - short and to the point. These have been compiled and condensed to provide a better understanding of the physiology, volume, benefits and conditions that occur from the production of gastric acid. 
The average horse produces 16 gallons of gastric acid daily.

Did You Know?

1.   Horses, donkeys and mules produce gastric acid continuously in preparation for constant uptake.
2.   The average 1,000 pound horse produces 16 gallons a day of gastric/hydrochloric acid. That equates to .66 gallons per hour (16 gallons divided by 24 hours). The stomach only has a 2 to 4 gallon capacity.

3.   Chewing and swallowing activate saliva production (an alkaline substance). Saliva buffers gastric acid by increasing the pH of the stomach.

4.   Stress, travel and medications can increase stomach acid levels.

5.   Never exercise or transport your horse on an empty stomach. Fiber creates a mat of sorts, which prevents acid from splashing in the stomach. An empty stomach allows accumulated unbuffered (lack of saliva from chewing) gastric acid to slosh and bathe its lining.

6.   Gastric acid left unbuffered is the leading cause for gastric ulcers followed by stress. Ulcers can develop in as little as 24 hours - and recur in 24 hours respectively.

7.   Researchers have determined that gastro-esophageal reflux can occur in horses despite the tight sphincter that separates the esophagus and stomach by characterizing esophageal lumen pH.

8.   Ulcerations as a result of unbuffered hydrochloric acid occur in the entrance of the duodenum as well as the stomach.
9.   According to Martine Hausberger, PhD, director of the Laboratory of Animal and Human Ethology, a branch of the French national research center (CNRS) and the University of Rennes, "It is also known that horses can experience gastrointestinal discomfort if deprived of food for a mere one to two hours.”

10.  Using proton pump inhibitors (Omeprazole) long term can have adverse effects. Long term stomach acid suppression can affect protein digestion and risk of vitamin and mineral deficiencies. Gastric acid serves a crucial and intricate role in overall digestion.

11.  Gastric acid is an important component of the immune system. It’s the first line of defense from ingested harmful microorganisms.

12.  The crucial and initial stages of digestion by gastric acid are not fully realized if feedstuff exits quickly. The faster feedstuff is consumed, the less time it spends in the stomach buffering acid. Once the stomach becomes two-thirds full it begins to empty regardless of how well the particles are prepared to advance to the small intestine.

​Taking Everything into Account

​The pH environment of the stomach requires a balancing act easily achieved in nature, where horses graze/forage 16-20 hours a day - ingesting small amounts as they move from place to place.

We hope these facts help illustrate the importance of free choice forage (loose or slow fed hay or pasture with or without a muzzle) for horses, donkeys and mules as nature intended. 

​Helpful How to Resources


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Monique Warren, Hay Pillow Founder with the Hay Pillow Slow Feeder product line - standard ground hay pillow, mini hay pillow, hanging hay pillow & horse trailer manger hay pillow

About the Author

Monique Warren invented the Hay Pillow® slow feeder and is the owner of Hay Pillow Inc. ​Warren has been an equine guardian for over forty years and slow-feed advocate for over 10 years. She contributes equine nutrition, digestive and hoof health articles to publications such as Equine Wellness, The Journal, The Naturally Healthy Horse, Natural Horse Magazine, Nicker News, The Horse's Hoof and Miniature Horse World Magazine. Equine nutrition and horses feet are her passions. She resides in Southern California.

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