Understanding Equine Digestion: How Horses Process Feed

Published on: December 21, 2024

By: Miles HenryFact Checked

A horse’s digestive system is uniquely adapted to their evolutionary history as grazing animals, designed for continuous, small-intake feeding throughout the day. Understanding the intricacies of equine digestion is vital for maintaining their health and well-being.

This guide provides horse owners with the knowledge they need to make informed decisions about feeding practices by exploring the mechanics of digestion, feeding practices, and providing practical tips to optimize your horse’s digestive health.

How Horses Digest Feed: An Overview

The equine digestive system is divided into two main parts: the foregut (mouth, esophagus, stomach, and small intestine) and the hindgut (cecum, large colon, small colon, and rectum). The foregut is responsible for initial digestion and nutrient absorption, while the hindgut focuses on fermenting fiber. Each plays a unique role in processing feed efficiently.

The Foregut: Where Digestion Begins

The foregut initiates the digestive process by breaking down food physically and chemically.

• Mouth: Chewing (mastication) reduces feed particle size and mixes it with saliva, which contains enzymes and buffers stomach acid. Proper dental care is essential for effective chewing.
• Esophagus: Peristalsis (muscular contractions) moves food to the stomach. Horses cannot regurgitate, making esophageal obstructions, like choke, serious concerns.
• Stomach: Representing only 9-10% of the digestive tract, the horse’s stomach mixes feed, initiates protein digestion with acid and pepsin, and releases it gradually into the small intestine. It produces acid continuously, requiring regular feed intake to prevent ulcers.
• Small Intestine: Most nutrient digestion and absorption occur here. Enzymes from the pancreas and bile from the liver (horses lack a gallbladder) aid in breaking down carbohydrates, proteins, and fats.

The Hindgut: The Fermentation Powerhouse

The horse’s hindgut is a critical component of its digestive system, acting as a fermentation powerhouse where a diverse community of microorganisms—bacteria, fungi, and protozoa—work together to maintain digestive health. This microbial community, known as the microbiome, plays an essential role in breaking down fiber and supporting overall health.

In simple terms the horse’s hindgut converts fibrous feeds into usable energy.

• Cecum: Functions as a fermentation vat where microbes break down dietary fiber.
• Large Colon: Home to billions of microorganisms that convert fiber into volatile fatty acids (VFAs), which provide energy.
• Small Colon: Absorbs water and forms fecal balls.
• Rectum: Expels waste as manure.

Fiber as the Primary Energy Source

Horses are herbivores, and their digestive systems are uniquely adapted to process plant-based materials. Dietary fiber, found in forages like hay and pasture, is the foundation of their diet. It consists of structural carbohydrates that are not digested in the foregut (stomach and small intestine). Instead, fiber undergoes fermentation in the hindgut (cecum and large colon), making it the primary source of energy for horses.

The Role of the Hindgut Microbiome

The hindgut houses a vast community of microorganisms, including bacteria, fungi, and protozoa, collectively known as the microbiome. These microbes are essential for breaking down fiber through fermentation, as horses lack the necessary enzymes to digest fiber themselves.

• Volatile Fatty Acid (VFA) Production: During fermentation, the microbiome converts fiber into VFAs such as acetate, propionate, and butyrate. These VFAs are absorbed through the walls of the hindgut and provide up to 70% of the horse’s energy needs, supporting overall performance and well-being.

Maintaining a Balanced Microbiome

A healthy microbiome is crucial for efficient fiber digestion and VFA production. However, the composition of the microbiome is highly sensitive to dietary changes, and imbalances can lead to serious health issues:

• Sudden Diet Changes: Abruptly switching hay types or introducing grains too quickly can disrupt the microbial balance.
• Starch Overload: Excessive starch reaching the hindgut lowers pH levels, which kills beneficial fiber-digesting microbes and promotes harmful bacteria. This can result in gas production, colic, and laminitis.

Fiber’s Role in Gut Health

Adequate fiber intake is critical for a healthy gut environment:

• Microbial Diversity: Fiber provides the substrate needed to maintain microbial diversity and activity, supporting digestive health.
• Stable Digestion: Insufficient fiber can cause microbial imbalances, leading to digestive issues, reduced energy production, and poor nutrient absorption.

Continuous Access to Roughage

Horses are natural grazers, and continuous access to long-stem forage like hay or pasture:

• Supports Natural Behavior: Promotes grazing habits that are essential for their mental and physical well-being.
• Buffers Stomach Acid: Helps reduce the risk of gastric ulcers by buffering stomach acid.
• Encourages Water Intake: Fiber-rich forage increases water consumption, which is critical for hydration and digestion.

Key Takeaway

Fiber is essential for a horse’s digestive health, primarily through the fermentation process in the hindgut, and forage is the foundation of a horse’s diet because it provides the structural carbohydrates and fiber necessary for proper digestion and energy production.

Diets should be formulated so that forage is the primary component, with other feeds supplementing the forage. Fiber is not just a filler in a horse’s diet—it is their primary energy source and a cornerstone of digestive health. The fermentation process in the hindgut, driven by a healthy microbiome, converts fiber into VFAs that fuel the horse’s body. Maintaining adequate fiber intake and a balanced microbiome through thoughtful feeding practices ensures proper digestion, energy production, and overall well-being.

Key Feeding Practices for Healthy Digestion

Forage, including hay and pasture, provides the essential fiber that forms the foundation of a horse’s diet. Horses have evolved to graze continuously on fibrous grasses, with digestive systems perfectly suited to this natural feeding behavior.

Supporting your horse’s digestive health begins with proper feeding practices, which not only help prevent common issues but also enhance nutrient absorption and overall well-being.

1. Forage First

A forage-based diet is essential for the horse’s natural digestive process.

• Recommendation: Forage should comprise at least 50% of the horse’s daily intake, with continuous access to roughage to support natural feeding behavior and a healthy hindgut microbiome.
• Why it Matters: Long periods without forage can lead to gastric ulcers, as the stomach produces acid continuously and needs feed to buffer it.

2. Small, Frequent Meals

Horses are natural grazers, designed to eat small amounts continuously.

• Recommendation: Feed small portions throughout the day to mimic natural grazing habits. Large meals, especially of concentrates, can overwhelm the foregut and lead to undigested starch reaching the hindgut.
• Why it Matters: Smaller, frequent meals improve nutrient absorption, prevent digestive upset, and reduce the risk of hindgut acidosis.

3. Limit Starch Intake

Starch, found in grains, provides energy but must be carefully managed.

• Recommendation: Keep starch intake to no more than 2 g/kg of body weight per meal. For a 1,000-pound horse, this equates to less than 4.4 pounds of high-starch feed per meal.
• Splitting Grain Meals: If your horse’s daily grain exceeds 0.5% of their body weight, divide the ration into two or more feedings. For instance, a 1,000-pound horse consuming more than 5 pounds of grain daily should have it split into at least two meals spaced 10–12 hours apart.
• Why it Matters: Excess starch that is not digested in the small intestine can reach the hindgut, disrupting the microbial balance and leading to colic, gas, or laminitis.

4. Hay Before Grain

Feeding hay before concentrates can protect your horse’s stomach.

• Recommendation: Offer hay before grain to slow the passage of feed through the digestive system, allowing better digestion and reducing the risk of gastric ulcers.
• Explore More: Learn the Best Practices for Feeding Horses Hay.

5. Gradual Diet Changes

Horses’ sensitive digestive systems require time to adapt to new feeds.

• Recommendation: Make dietary changes gradually over 7–10 days to allow the hindgut microbiome to adjust.
• Why it Matters: Sudden changes can disrupt the microbial population, leading to colic or digestive upset.

6. Provide Alternative Fiber Sources

When forage is limited, alternatives can supplement the diet.

• Recommendation: Use beet pulp or soy hulls as additional fiber sources. Soak beet pulp before feeding to improve digestibility and prevent choke.
• Why it Matters: These alternatives maintain fiber intake, especially during hay shortages, and support healthy digestion.

7. Fresh Water Availability

Water is essential for every aspect of digestion and health.

• Recommendation: Ensure constant access to fresh, clean water. After exercise, monitor intake to prevent dehydration or choke. Learn more about Nutritional Management for Horses.
• Why it Matters: Water helps soften feed for digestion, supports hydration, and prevents issues like esophageal blockages.

Monitoring Water Intake to Support Equine Digestion

Hydration is essential for healthy digestion in horses, and I make it a priority to monitor their water intake daily. Here’s what works for me:

Daily Checks

• Track Consumption: I measure water intake in buckets or monitor trough levels daily. Horses usually drink 5–15 gallons per day.
• Dehydration Signs: I perform a quick skin pinch test and check gums for dryness or paleness—key dehydration indicators.

Encouraging Drinking

• Warm Water in Winter: Slightly warming water during cold weather encourages drinking.
• Add Flavor: A splash of apple juice or electrolytes can entice picky drinkers.
• Provide Salt: I ensure access to salt blocks or mix electrolytes into feed during hot weather or after exercise.

Clean Water Practices

• Regular Cleaning: I scrub water buckets and troughs weekly to keep water fresh and appealing.
• Check Waterers: If using automatic waterers, I inspect them daily to ensure they’re functioning.

After Exercise

• Gradual Rehydration: I let my horses cool down before offering larger amounts of water, starting with small sips.
• Soaked Feed: I occasionally soak oats to provide additional hydration, especially for horses prone to dehydration.

By keeping water clean, monitoring intake, and encouraging regular drinking, I support my horses’ digestion and overall health. Consistent hydration prevents issues like colic and ensures the digestive system functions smoothly.

Why These Practices Matter

To mimic natural grazing habits and improve nutrient absorption, feed small portions throughout the day. Large meals, especially of concentrates, can overwhelm the foregut and lead to undigested starch reaching the hindgut, causing digestive upset and hindgut acidosis.

Feeding strategies aligned with a horse’s natural grazing behavior, such as providing small frequent meals and adequate forage, will promote digestive health and well-being, reduce the risk of digestive upset, and optimize nutrient absorption.

Explore Nutritional Management for Horses from Purdue University Cooperative Extension

Different Forages and Their Suitability

Hay and Pasture

• Pasture: Pasture is the most natural feed for horses, allowing them to graze and consume small amounts of feed over extended periods, which aligns with their digestive physiology. Pasture grasses are a good source of fiber and water-soluble carbohydrates (sugars), though sugar content varies. Lush pastures, for example, tend to have higher sugar levels.
• Hay: Hay serves as a crucial alternative to pasture and is a primary source of fiber for horses. Its nutritional value depends on factors like the type of grass, maturity at harvest, and curing process.

Types of Hay

• Grass Hays are lower in protein and calcium than legume hays and are recommended as the foundation of a horse’s diet due to their essential fiber and lower non-structural carbohydrate content.
• Legume hays are higher in protein, calcium, and energy, making them beneficial for horses with higher nutritional needs, but should be fed in moderation to avoid digestive upset. Alfalfa is the most popular legume hay for horses.
• Mixed Hays: Combine grasses and legumes, offering a balanced nutritional profile.

Maturity and Quality

• Mature Forages: More stemmy with higher lignin content, making them less digestible and lower in nutritional value.
• Immature Forages: Leafy and more digestible, offering higher nutrient availability. These resemble the digestibility levels of feed suitable for ruminants like cattle.

Considerations

• Long-Stem Forages: Loose hay promotes chewing and salivation, which buffers stomach acid. It also slows food passage through the digestive tract, improving digestion.
• Processed Forages: Options like hay cubes, pellets, or chopped hay can be helpful, especially for horses with dental issues. However, they do not provide the same benefits as long-stem forages.
• Tailoring Forage to Needs: The appropriate forage type depends on the horse’s age, activity level, and health status. Consulting a veterinarian or equine nutritionist is recommended.
• Gradual Changes: Forage transitions should be made gradually over 7–10 days to allow the hindgut microbiome to adapt. Abrupt changes can disrupt the microbial balance, causing digestive upset.

One winter, my mare, Diamond, lost her coat’s shine despite a diet of quality grass hay. After adding a mix of alfalfa for more protein and calcium, her shiny coat returned, and her energy increased. In contrast, my gelding, Corked, struggled with rolled oats until I transitioned him to extruded feed, which improved his digestion and stabilized his weight. These experiences taught me to tailor forage and grain choices to each horse’s needs, with noticeable results in health and performance.

Grain Processing for Improved Digestibility

Why Process Grains?

Grains, such as oats, are an important source of non-structural carbohydrates (starch), providing energy for horses. Processing grains enhances the digestibility of starch in the small intestine, reducing the amount that reaches the hindgut.

This is because some unprocessed grains have a hard seed coat that limits starch availability for digestion. If starch bypasses the small intestine, it is rapidly fermented by bacteria in the hindgut, leading to lactic acid production, hindgut acidosis, and other health issues.

Types of Grain Processing

Grain processing makes digestibility easier for horses by breaking down hard seed coats, making nutrients more accessible for absorption. Here are the key methods:

• Cracking, Rolling, and Flaking: Increase surface area for digestive enzymes, ideal for sensitive digestive systems.
• Pelleted Feeds: Convenient and consistent in nutrients but often consumed quickly.
• Extruded Feeds: Improve digestibility and encourage slower consumption, aiding digestion.
• Micronizing: Uses infrared heat to enhance starch digestibility and palatability.

Each method varies in its impact, with softer grains like oats requiring minimal processing compared to harder grains like corn. Consult a veterinarian or nutritionist to determine the best choice for your horse’s needs.

Impact on Digestibility and Nutrient Availability

• Improved Starch Digestion: Processing grains makes starch more accessible for small intestine digestion, reducing the risk of undigested starch fermenting in the hindgut.
• Increased Nutrient Availability: Processing also enhances the availability of other nutrients, such as protein, by breaking down the seed coat.
• Varying Digestibility: Different grains, such as corn, oats, and barley, have varying starch digestibility. Processing helps mitigate these differences.
• Rate of Consumption: Processing methods influence how quickly horses eat. Pelleted feeds tend to be eaten faster, while extruded feeds are consumed more slowly, which can affect digestion and feeding behavior.

Considerations

• Not All Grains Require Processing: Softer grains like oats may need minimal processing compared to harder grains like corn or milo.
• Avoid Fine Particles: Finely ground feeds can pass through the digestive tract too quickly, reducing digestion time and increasing the risk of gastric upset.
• Tailored to Individual Needs: The choice of processing method should account for the horse’s age, dental health, activity level, and specific nutritional requirements.
• Consult an Expert: A veterinarian or equine nutritionist can recommend the most appropriate grain processing method based on your horse’s unique needs.

Common Digestive Issues

Digestive issues often stem from the horse’s unique digestive physiology, especially the hindgut fermentation process, and are significantly influenced by feeding management practices. Prioritizing forage, avoiding large grain meals, ensuring proper dental care, and providing constant access to fresh water are essential to prevent these common digestive problems.

Digestive Issue	Definition	Underlying Mechanisms	Key Risk Factors
Colic	Abdominal pain in horses; a symptom, not a disease	– Gas accumulation from fermentation. – Impaction from blockages. – Stress-induced intestinal spasms. – Intestinal displacement or torsion. – Dysbiosis from dietary changes.	– Sudden diet changes. – Low fiber intake. – Large grain meals. – Poor water access. – Dental issues.
Laminitis	Painful condition of the sensitive laminae in the hooves	– Hindgut acidosis from starch fermentation. – Endotoxin release from microbial death. – Inflammation and reduced blood flow to hooves.	– Excessive grain/concentrate intake. – Rapid diet changes. – Overgrazing lush pastures.
Choke	Esophageal blockage caused by lodged food bolus	– Feed lodging in esophagus. – Insufficient chewing of food. – Dry feeds swelling in esophagus.	– Poor dentition. – Eating too fast. – Lack of water. – Dry or unmoistened feed.

Additional Insights for Optimal Nutrition

To further enhance feeding strategies, consider these additional points:

• Grain Processing:
  • Processing grains, such as rolling, cracking, or extruding, improves digestibility by breaking down hard seed coats, making nutrients more accessible for absorption in the small intestine.
  • For instance, extruded feeds are particularly beneficial for older horses with reduced chewing efficiency.
• Individual Variation:
  • Tailor feeding practices to the horse’s age, activity level, and health conditions. Consult an equine nutritionist or veterinarian to ensure the feeding plan meets your horse’s unique needs.
  • For example, a performance horse may require higher energy feeds compared to a retired pasture horse.
• Social Feeding Environment:
  • Minimize stress during feeding by considering herd dynamics. Providing adequate spacing or individual feeding stations can help reduce competition. Turnout and access to forage throughout the day also alleviate anxiety and support natural grazing behavior.

During colder months I heat whole oats in a bucket of water using a heating wand can make nutrients more accessible and easier to digest. Ensure the oats are warmed evenly and fed immediately to retain their nutritional value.

Practical Tips for Monitoring Digestive Health

1. Observe Behavior:
   • Watch for signs of discomfort like lethargy, weight loss, reduced appetite, or changes in manure consistency.
2. Focus on High-Quality Forage:
   • Mature, stemmy forages are less digestible; prioritize leafy, immature hay.
3. Monitor Body Condition:
   • Regularly assess weight and adjust feed as needed.
4. Include Long-Stem Forage:
   • Encourage chewing and saliva production with long-stem hay or pasture.

Key Feeding Practices for Healthy Digestion

Recommendation	Details	Why?	Potential Consequences	Relevant Section
Forage First	* Base diet on forage. * Ensure constant access.	* Provides essential fiber. * Prevents ulcers due to constant acid production.	Digestive upset, gastric ulcers.	Foregut Function, Key Practices.
Small, Frequent Meals	* Divide daily ration into small meals. * Feed throughout the day.	* Matches natural grazing. * Avoids overwhelming the digestive system.	Digestive upset.	Key Practices.
Limit Starch	* Avoid large grain meals. * Ensure starch is digested in the small intestine.	* Prevents hindgut pH imbalance. * Maintains a healthy microbiome.	Colic, acidosis, laminitis.	Hindgut Function, Key Practices.
Max Starch Intake	* No more than 2g starch/kg body weight per meal.	* Prevents excess starch reaching hindgut.	Hindgut acidosis, laminitis.	Key Practices.
Hay Before Concentrates	* Offer hay before grain.	* Slows feed passage. * Reduces ulcer risk.	Gastric ulcers.	Key Practices.
Gradual Diet Changes	* Make changes slowly over 7-10 days.	* Allows microbiome to adapt. * Prevents upset.	Digestive upset, colic.	Key Practices.
Continuous Roughage	* Provide constant access to roughage.	* Mimics grazing. * Prevents upset and boredom.	Gastric ulcers, behavioral issues.	Key Practices, Common Issues.
Fresh Water	* Always available. * Monitor intake after exercise.	* Aids digestion. * Prevents dehydration and choke.	Dehydration, choke.	Key Practices.

FAQs About Equine Digestion

Conclusion: Understanding Equine Digestion: How Horses Process Feed

Understanding equine digestion is key to providing optimal care and avoiding health issues. By prioritizing forage, feeding small meals frequently, and maintaining consistent feeding practices, horse owners can support their horses’ well-being and performance. Always consult a veterinarian or equine nutritionist to tailor feeding plans to your horse’s unique needs.

We’d love to hear from you! What feeding strategies have worked for your horse? Share your experiences and tips in the comments below to help build a community of knowledgeable and caring horse owners.