Gastric acid plays a central role in the equine digestive system.
Both excessive and insufficient gastric acid can disrupt the delicate balance within the stomach — affecting digestion, overall well-being, and performance.

This article explains how gastric acid works in horses, what disrupts its balance, and how feeding and management influence gastric health.

Content

• A brief overview of the equine stomach
• What is gastric acid?
• Functions of equine gastric acid
• Natural counterbalances
• ph-levels - research-based
• Disrupting factors
• Neutralizing gastric acid - what actually helps
• Myths
• FAQ

A brief overview of the equine stomach

The equine stomach consists of two very different regions that respond to gastric acid in distinctly different ways:

The glandular region (lower part)

This is where gastric acid is produced. The glandular region is well protected by a thick mucus layer and can tolerate extremely low pH levels without difficulty.

The non-glandular region (upper part)

This section has little intrinsic protection against acid. If the pH level drops too far—such as during prolonged fasting periods or after starch-rich meals—the mucosal lining becomes irritated quickly.

The transitional zone between these two regions is particularly sensitive. Many acid-related problems develop precisely in this area, especially when the stomach remains empty for extended periods or when feeding rhythms do not align with the horse’s natural biology.

For a more detailed explanation of the equine stomach and its mucosal lining, you can find further information on our dedicated equine gastric ulcer topic page.

Gastric ulcers (EGUS: Equine Gastric Ulcer Syndrome) can develop in both regions of the equine stomach.
When ulcers occur in the upper, non-glandular region, they are referred to as ESGUS (Equine Squamous Gastric Ulcer Syndrome). Ulcers affecting the lower, glandular region are classified as EGGUS (Equine Glandular Gastric Ulcer Syndrome).

Ulcers in the glandular stomach are considerably less well studied. There is still limited robust scientific evidence regarding the causes of ulcer formation in this otherwise well-protected region.

What is gastric acid?

Gastric acid is not a homogeneous fluid but a complex mixture of different components that work together to enable digestion in the stomach and prepare ingested feed for further digestion in the intestines.

The main components of gastric acid include:

Hydrochloric acid (HCl)

Hydrochloric acid is responsible for the very low pH level of approximately 1–2 in the lower part of the stomach. It breaks down feed structures and creates the conditions required for digestive enzymes to function.

Pepsinogen / Pepsin

Pepsin is a protein-digesting enzyme that becomes active only in an acidic environment. Without this activation, horses cannot utilize dietary protein efficiently.

Mucus and electrolytes

These components protect the stomach lining in the glandular region and help stabilize the chemical environment.

The contents of a horse’s stomach are never static. Depending on feeding practices, chewing activity, and stress levels, the relative proportions of acid, mucus, feed particles, and enzymes are constantly changing.

Functions of equine gastric acid - why it is essential

Gastric acid is often viewed primarily as a “risk,” yet it fulfills several vital functions within the equine digestive system. What matters is not the acid itself, but how well it is regulated and where it acts.

Initiating protein digestion

Gastric acid activates the enzyme pepsin, which begins breaking down proteins in the stomach. Without a sufficiently low pH level, pepsin remains inactive, and undigested proteins pass into the intestine, where they may promote abnormal fermentation.

Protection against pathogens and harmful substances

The extremely low pH reduces the microbial load in feed and water. Bacteria, mold spores, and yeasts that naturally occur in forage are largely rendered harmless under acidic conditions.

Regulation of gastric emptying

Gastric acid influences the timing at which stomach contents are passed into the small intestine. Both excessively high and excessively low acid levels can disrupt this regulation, with consequences for the entire digestive process.

Preparing feed for further digestion

Gastric acid breaks down feed structures, denatures proteins, and prepares plant fibers so they can be more efficiently utilized in the intestines.

In short:
Gastric acid is indispensable. Problems arise only when it comes into contact with the stomach lining for too long, in overly concentrated form, or in unfavorable areas.

How much gastric acid does a horse produce?

Horses produce up to 30 liters of gastric juice per day.

Natural counterbalances to gastric acid

To maintain balance in the equine stomach despite continuous acid production, several effective protective mechanisms are in place. However, these mechanisms function optimally only when feeding practices and management align with the horse’s natural biology.

1. Saliva - the most important natural acid buffer

Saliva contains significant amounts of bicarbonate, which neutralizes gastric acid and raises gastric pH.

Important to know:

• Horses produce saliva only while chewing—not when simply consuming soft concentrate feeds, not when licking, and not spontaneously.
• The longer the chewing time, the more saliva is produced.
• Forage is therefore the most important key to natural pH stabilization.

2. Forage - mechanical protection against acid contact

Fiber-rich forage forms a type of “protective mat” within the stomach that:

• keeps gastric acid in the lower, glandular region
• protects the sensitive upper region from direct acid contact

If this fibrous structure is lacking, acid can more easily move upward and irritate the mucosal lining. In addition, forage stimulates chewing activity, leading to increased saliva production.

3. Mucus - the most important endogenous protection in the lower stomach

The glandular region of the stomach protects itself from gastric acid through:

• a thick, viscous mucus layer (mucin layer)
• prostaglandins that promote mucus production and blood flow
• a very high rate of cell turnover, allowing minor damage to be repaired quickly
• a dense cellular barrier that prevents acid from penetrating deeply into the tissue

A closer look: Why prostaglandins are essential for gastric protection

Prostaglandins are endogenous signaling molecules that serve two central protective functions in the stomach:

• They promote the production of the protective mucus layer.
• They improve blood flow to the gastric mucosa, allowing minor damage to be repaired quickly. 

Studies show that anti-inflammatory pain medications such as phenylbutazone or flunixin can increase the stomach lining’s susceptibility to injury because they inhibit the production of protective prostaglandins. As a result, mucus production, blood flow, and mucosal repair mechanisms are weakened—making the gastric lining more sensitive, even when gastric acid production is normal (Flood & Stewart, 2022).

Gastric mucosal problems often arise not because there is too much acid, but because the body’s own protective systems are compromised.

ph-levels in the equine stomach - research-based findings

pH levels within the equine stomach are neither uniform across all regions nor constant over time. They vary depending on stomach region, feeding patterns, stress, and physical activity. Modern 24-hour pH monitoring provides a very clear picture:

Glandular region (lower part): pH 1 - 2

This region is responsible for gastric acid production and is designed to tolerate a persistently highly acidic environment.

Typical characteristics:

• consistently low pH level
• only minor fluctuations throughout the day
• ideal conditions for pepsin activity and the initial digestion of proteins
• gastric mucosa is usually well protected

Non-glandular region (upper part): ph 3 - 7

This region is significantly more sensitive to acid exposure. Studies show that:

• pH levels fluctuate widely depending on feed intake
• pH drops rapidly into the acidic range during feed deprivation or after starch-rich meals
• pH rises again once forage is chewed (increased saliva, greater buffering capacity)

In this context, feeding management largely determines how well the gastric lining is protected.

Factors that disrupt gastric acid balance

Many gastric problems are not caused by “too much acid,” but by prolonged acid exposure in areas that are not adequately protected. Several factors can disrupt this delicate balance:

Prolonged feeding gaps (longer than 4-5 hours)

Prolonged feeding gaps are one of the most significant risk factors for excessively low pH levels in the upper, non-glandular region of the stomach.

Why does this matter?

• chewing stops → saliva production stops → buffering capacity is lost
• gastric acid continues to be produced
• acid can more easily reach unprotected areas

Large amounts of concentrate feed

Concentrate feed affects the gastric acid environment in several ways:

• reduced chewing time → less saliva → less natural buffering
• faster gastric emptying, as concentrates are energy-dense, do not form a fibrous mat, and pass through the stomach more quickly
• absence of a protective fiber layer like the one forage creates in the stomach

Starch-rich concentrates (such as grains) are particularly problematic:

• starch leads to a faster and more pronounced drop in pH

• it promotes the formation of volatile fatty acids

• and can further irritate the sensitive gastric lining

A brief note:
Concentrate feed is not inherently harmful — not even for horses with sensitive stomachs. What matters most are the composition of the feed, the timing of feeding, and the amount offered.

Forage should always be fed before concentrates. After around 30 minutes, sufficient saliva (bicarbonate) has already been produced, and a protective fiber mat has formed in the stomach, helping to shield the sensitive upper region from acid contact.

For a more in-depth discussion, see our topic pages on feeding horses with gastric issues.

Stress and environmental disruption

Stress does not necessarily lead to “more acid,” but it affects the stomach in other, equally important ways:

• gastric emptying slows down
• acid remains in sensitive areas for longer periods
• many horses eat less when stressed → resulting in reduced saliva production

The result: acid exposure is prolonged.

• excessive stable noise
• competition or tension around feeding
• social hierarchy conflicts
• irregular daily routines
• frequently changing caregivers or handlers

For a more detailed discussion of stress and its impact on the equine stomach, see our dedicated topic page on stress in horses.

Training: the „acid splash“-effect

During exercise, movement causes stomach contents and gastric acid to be pushed upward within the stomach. This becomes particularly problematic when:

• the stomach is empty

• little or no forage has been consumed beforehand

• the horse is already experiencing stress or excessive acid exposure

In these situations, acid can more easily come into contact with sensitive areas of the stomach.

Offering a small portion of hay 30–60 minutes before riding can significantly reduce this effect.

Transport & routine changes

Transport is well documented in scientific studies:

• gastric pH levels decrease measurably

• horses often eat little or not at all

• stress and feed deprivation reinforce each other

Changes in daily routines or a stable change can also temporarily disrupt gastric acid balance.

Imbalance between gastric acid and protective mechanisms

All of the factors described above ultimately lead to the same underlying problem:

Gastric acid comes into contact more intensely or for longer periods with areas that lack adequate protection or where protective mechanisms are impaired.

The consequences may include:

• irritation of the gastric mucosa

• changes in the gastric pH environment

• secondary issues in the intestines

• impaired digestion and nutrient utilization

• pain and reduced performance

Neutralizing gastric acid or supportingprotective mechanisms – what actually helps

Gastric acid is not inherently harmful. What matters is that it does not reach the sensitive upper region of the stomach in an uncontrolled manner and that the protective mechanisms in the lower, glandular region function properly.

There are several ways to support gastric acid balance. A detailed comparison of gastric protectants, acid buffers, and acid blockers can be found here:

What is the difference between gastric protectants, acid buffers, and acid blockers?

In brief

Acid blockers – only with clear medical indication

Medications such as omeprazole drastically reduce gastric acid production. They are essential in cases of diagnosed gastric ulcers but are not suitable for long-term preventive use, as they alter the stomach’s natural environment. Without gastric acid, it cannot fulfill its essential roles in digestion.

Natural acid buffers – binding excess acid

Buffering agents such as calcium carbonate or specific algae-based products can bind excess acid without completely suppressing the necessary production of gastric acid.

This also includes Equine 74 Gastric: it binds excess acid and stabilizes gastric pH over a longer period without blocking digestive function.

Gastric protectants - supporting the mucosal lining

Gastric protectants do not act on acid itself but instead support the gastric mucosa. Particularly suitable are pectin-rich feeds such as unsweetened beet pulp. In combination with gastric acid and saliva, pectins can form a gel-like protective layer that temporarily relieves the gastric lining.

Pectin-containing supplements have shown positive effects on the gastric mucosa and lesions in individual studies (e.g., Woodward et al., 2014), but they are not a guarantee. Their effectiveness depends heavily on feeding practices, feeding intervals, overall health, and management.

Myths & misconceptions about gastrc acid

There are many widespread assumptions surrounding gastric acid and gastric protection that repeatedly lead to poor decisions in practice. These myths persist stubbornly—even though they have been scientifically disproven.

Myth 1: „Gastric acid is inherently harmful.“ 

Fact:

Gastric acid is essential for life. It activates digestive enzymes, protects against pathogens, and ensures that feed is properly digested.

Problems do not arise from gastric acid itself, but rather from factors such as:

• inappropriate feeding management

• prolonged feeding gaps

• stress

• large amounts of concentrate feed

Gastric acid is not the enemy—imbalance is.

Myth 2: „Acid blockers like omeprazole can simply be used peventively.“

Fact:
Omeprazole strongly suppresses gastric acid production. This can be appropriate during the acute phase of a diagnosed gastric ulcer—but it can be problematic in otherwise healthy horses.

Why?

Reduced gastric acid impairs protein digestion, as pepsin is less active at higher pH levels. In addition, an important defense mechanism against pathogens and bacteria ingested with feed is lost.

After discontinuation, short-term rebound effects (excessive acid production) may occur.

Prevention is most effective when based on feeding practices, adequate chewing time, stress reduction, and pH-stabilizing feeds—not on acid blockers.

Myth 3: „Acid-related problems automatically mean gastric ulcers.“

Fact:
An irritated stomach does not automatically mean that a gastric ulcer is present. However, gastric ulcers can develop very quickly. For this reason, it is worth staying attentive and consulting a veterinarian if ulcers are suspected.

A definitive diagnosis can only be made by gastroscopy.

Myth 4: „Hay fed ad libitum is sufficient gastric protection.“

Fact:
Hay is the most important foundation—but it does not provide complete protection on its own.

This is because:

• even with ad libitum hay, factors such as stress, transport, training, or environmental disruption can influence gastric pH
• individual sensitivity varies greatly between horses
• pH-stabilizing supplements may still be beneficial

Myth 5: „If my horse eats poorly, it must have too much gastric acid.“

Fact:
Loss of appetite can have many different causes, including:

• dental problems

• pain

• metabolic disorders

• stress

• intestinal issues

• irritation of the gastric mucosa (not necessarily caused by excess acid)

An “excess of gastric acid” is therefore only one of many possible explanations. Many symptoms commonly attributed to stomach problems can just as well result from entirely different underlying conditions.

A reliable assessment is only possible when all findings are considered together—including feeding practices, behavior, clinical examination, and, if indicated, gastroscopy.

FAQ - Gastric acid in horses

Sources

Woodward, M. C., Huff, N. K., Garza, F., Keowen, M. L., Kearney, M. T., & Andrews, F. M. (2014).
Effect of pectin, lecithin, and antacid feed supplements on gastric ulcer scores, gastric fluid pH and blood gas values in horses. BMC Veterinary Research, 10(Suppl 1), S4. https://doi.org/10.1186/1746-6148-10-S1-S4

Damke, Cornelia & Snyder, Alice & Uhlig, Albrecht & Coenen, Manfred & Schusser, Gerald. (2015). Impact of diet on 24-hour intragastric pH profile in healthy horses. Berliner und Münchener tierärztliche Wochenschrift. 128. 345-349. 10.2376/0005-9366-128-345.

Bell, R. J. W., Mogg, T. D., & Kingston, J. K. (2007). Equine gastric ulcer syndrome in adult horses: A review. New Zealand Veterinary Journal, 55(1), 1–12. PDF: https://irp-cdn.multiscreensite.com/d048e3f1/files/uploaded/U-Equine%20gastric%20ulcer%20syndrome%20in%20adult%20horses.pdf

Paul, L. J., Ericsson, A. C., Andrews, F. M., McAdams, Z., Keowen, M. L., St Blanc, M. P., & Banse, H. E. (2022). Dietary and management factors influence the equine gastric microbiome. Journal of the American Veterinary Medical Association, 260(S3), S111–S120. https://doi.org/10.2460/javma.22.07.0277.

Masoud Ahmadnejad, Ghader Jalilzadeh-Amin, Benjamin W Sykes, Prophylactic effects of Glycyrrhiza glabra root extract on phenylbutazone-induced Equine Glandular Gastric Disease (EGGD), Journal of Equine Veterinary Science, Volume 118, 2022, 104088, ISSN 0737-0806, https://doi.org/10.1016/j.jevs.2022.104088.

Flood, J., & Stewart, A. J. (2022). Non-Steroidal Anti-Inflammatory Drugs and Associated Toxicities in Horses. Animals, 12(21), 2939. https://doi.org/10.3390/ani12212939

Vokes, J., Lovett, A., & Sykes, B. (2023). Equine gastric ulcer syndrome: An update on current knowledge. Animals, 13(7), 1261. https://doi.org/10.3390/ani13071261

Learn more 

On our dedicated topic page, you’ll find additional in-depth information and further resources on gastric ulcers in horses. The page also covers practical approaches to the prevention of gastric ulcers, with a focus on management and feeding strategies.