Gastric Acidity and Equine Health: More than Just a pH Number

The equine stomach operates differently from that of many other species. One of its most distinctive features is the continuous secretion of gastric acid, regardless of whether the horse is eating or fasting. While this physiological adaptation supports the horse's natural grazing behavior, it can also predispose horses to gastric irritation and ulceration when management practices do not align with their digestive needs¹. 

Continuous Acid Production 

Unlike humans, who produce significant amounts of stomach acid primarily in response to meals, horses secrete gastric acid around the clock (Murray, 1992; Merritt, 2003). As a result, the stomach remains acidic even during periods without feed intake. 

Gastric pH varies considerably within different regions of the equine stomach. In horses with unrestricted access to forage, pH values typically range from 1–2 in the fundic region, 4–5 near the margo plicatus, and 6–7 in the cardiac region². This variation reflects the unique anatomy and function of the equine stomach. 

The Role of Feeding in Gastric pH 

Diet and feeding patterns significantly influence gastric acidity. Studies have shown that fasting horses for 12–24 hours results in gastric pH values consistently around 2.0. In contrast, feeding hay before sampling increases gastric pH to approximately 3.1¹. 

This increase occurs for two important reasons. First, chewing forage stimulates saliva production, and saliva contains bicarbonate that helps buffer stomach acid. Second, feed physically dilutes gastric contents, reducing overall acidity. 

Additionally, high gastric pH readings may occasionally occur in fasted horses due to reflux of alkaline contents from the duodenum back into the stomach¹. 

Challenges in Measuring Gastric pH 

Accurately measuring gastric pH in horses presents several challenges. Horses with continuous access to forage often develop a mat of partially digested feed within the stomach, making precise placement of sampling equipment difficult. For this reason, fasting is commonly used before pH assessment. 

However, fasting itself can alter gastric conditions. Since horses continue to produce acid even when feed is absent, fasting may create a more acidic environment than would normally exist under natural grazing condition^1,2. 

Several techniques have been used to assess gastric pH, including endoscopic sampling, cannula-based measurements, indwelling pH electrodes, and nasogastric aspiration. Each method offers advantages and limitations related to accuracy, invasiveness, cost, and practicality^1,2. 

Implications for Equine Health 

Understanding gastric pH is critical because excessive acidity is a major contributor to gastric irritation and ulcer formation. Management practices that involve prolonged fasting, restricted forage access, or intermittent feeding schedules may expose the stomach lining to continuous acid without the protective buffering effects of feed and saliva¹. 

Maintaining regular forage intake remains one of the most effective ways to support normal gastric physiology and reduce the risk of acid-related gastric disease. 

Conclusion 

The horse's digestive system is designed for near-continuous forage consumption. Because gastric acid secretion continues regardless of feeding status, management practices that limit forage intake can significantly influence stomach pH and gastric health. Recognizing the factors that affect gastric acidity can help owners and veterinarians implement feeding strategies that better support equine digestive well-being. 

References

1. Garcia LN, McCall CA, McElhenney WH, Taintor JS, Schumacher JO. Gastric pH and cribbing frequency of horses treated with an oral antacid. The Professional Animal Scientist. 2015 Feb 1;31(1):57-62. https://www.appliedanimalscience.org/article/S1080-7446(15)30007-3/pdf
2. Merritt AM. The Equine Stomach: A Personal Perspective (1963-2003)(21-Nov-2003). S. l. https://www.researchgate.net/publication/267398195