The pH levels of the stomach vary depending upon the area that you examine. The pH varies from more basic (pH 6-7) near the cardiac sphincter (or closer to the end of the esophagus) to very acidic (pH 1-2) near the pyloric sphincter (near the duodenum). When your horse eats, the feedstuffs tend to layer in his stomach, depending on the density of the material. If the feed is low density, it will stay closer to the top, where saliva from the esophagus mixes with the feed and keeps the pH closer to neutral (pH of 7 is neutral). The higher the density of the feed material, the lower it settles, and it will end up in the glandular portion of the stomach, which has the lowest pH due to secretion of hydrochloric acid by the parietal cells. This part of the stomach has a mucous coating that protects it from the acid; however the upper portion of the stomach does not have this coating. There is an excellent article on the equine stomach (with good figures) that was presented at the 49th Annual Convention of the American Association of Equine Practitioners, 2003 – New Orleans, LA, USA. You can view this article at http://www.ivis.org/proceedings/AAEP/2003/merritt/chapter_frm.asp?LA=1#intragastric
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This work is supported in part by New Technologies for Agriculture Extension grant no. 2020-41595-30123 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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