Feed Allergies in Horses: True Allergy or a Gut Health Issue?

Dr Tania Cubitt & Dr Stephen Duren – Performance Horse Nutrition

Feed allergies are often blamed for a wide range of problems in horses—itching, hives, loose manure, behavioral changes, poor performance, and recurrent colic. But are these reactions truly caused by a food allergy, or are they more commonly linked to a breakdown in intestinal barrier function?

Current research suggests the answer is usually the latter.

True Feed Allergies: Rare but Real

A true feed allergy is an immune-mediated hypersensitivity reaction, typically involving IgE antibodies directed against a specific dietary protein. In horses, confirmed food allergies appear to be relatively uncommon compared with other species such as dogs or humans.

When true allergies do occur, they are most often associated with:

• Urticaria (hives)
• Facial or limb swelling
• Intense pruritus
• Rapid onset of signs following ingestion of a specific ingredient

These reactions tend to be consistent and repeatable, occurring every time the offending feed is consumed. While ingredients such as soy, alfalfa, and certain grains are frequently accused, documented cases remain limited in the scientific literature (Jackson et al., 2003; White, 2008).

The More Common Explanation: Impaired Intestinal Barrier Function

In contrast, many horses labelled as having “feed allergies” are more accurately experiencing feed sensitivities driven by increased intestinal permeability—often referred to as a compromised or “leaky” gut.

The intestinal lining acts as a selective barrier, allowing nutrients to be absorbed while preventing bacteria, endotoxins, and large antigenic proteins from entering systemic circulation. When this barrier is disrupted, partially digested proteins can cross the gut wall and stimulate an inappropriate immune response, even to feeds the horse has previously tolerated (Bischoff et al., 2014; Stewart et al., 2017).

What Causes Breakdown of the Gut Barrier?

Research has identified several factors that negatively affect intestinal integrity in horses:

• Transport and environmental stress
• High-starch or rapidly fermentable diets
• Abrupt dietary changes
• Non-steroidal anti-inflammatory drug (NSAID) use
• Dehydration or illness
• Chronic low-grade inflammation

Stress-related increases in cortisol and inflammatory mediators are known to alter tight junction proteins within the gut lining, increasing permeability and immune activation (McKenzie et al., 2015; Freeman & Janecka, 2017).

Why Elimination Diets Sometimes Appear to Work

Removing suspected ingredients often leads to improvement—not necessarily because the horse has a true allergy, but because reducing dietary complexity lowers antigen exposure and gives the gut lining time to recover. If underlying intestinal health is not addressed, however, horses frequently develop new “sensitivities” over time.

A More Effective Way to Think About Feed Reactions

Rather than focusing solely on identifying a single problematic ingredient, a more productive question is often:
“Why is this horse reacting now to feeds it previously tolerated?”

Supporting intestinal health through consistent forage intake, controlled starch levels, adequate hydration, stress management, and targeted nutritional support may reduce immune reactivity and improve long-term feed tolerance.

Nutrients That Support Intestinal Integrity and Immune Tolerance

If many feed reactions in horses are driven by compromised gut barrier function rather than true allergy, nutritional support should focus on strengthening the intestinal lining, stabilizing the microbiome, and moderating immune reactivity.

Poulin Grain approaches this by including nutrients that target multiple aspects of gut and immune health:

Probiotics
Probiotics support a balanced hindgut microbial population, helping maintain normal fermentation patterns and competitive exclusion of undesirable bacteria. A stable microbiome plays a key role in supporting intestinal barrier integrity and immune regulation.

Prebiotics
Prebiotics selectively nourish beneficial bacteria already present in the gut. By supporting microbial diversity and activity, prebiotics help reinforce the gut lining and reduce immune overstimulation caused by microbial imbalance.

Super Fibers
Highly fermentable fibers provide a steady fuel source for beneficial microbes and promote the production of short-chain fatty acids, which are critical for maintaining intestinal epithelial health. Consistent fiber fermentation supports gut resilience during stress or dietary change.

Natural Vitamin E
Natural-source vitamin E acts as a powerful antioxidant, supporting immune function and protecting intestinal cells from oxidative damage. Periods of stress, illness, or reduced forage intake can increase vitamin E demand, making adequate supply particularly important for gut and immune health.

KemTRACE® Chromium
Chromium supports normal glucose metabolism and stress response. By helping moderate cortisol and metabolic fluctuations, chromium may indirectly support immune balance and gut function during periods of physical or environmental stress.

Marine-Derived Calcium
Marine-derived calcium provides buffering support within the digestive tract and contributes to maintaining a stable gastrointestinal environment. Supporting normal gastric and intestinal conditions can help protect the integrity of the gut lining.

GIPro3®
GIPro3 combines functional proteobiotics designed to support intestinal barrier function, microbial balance, and normal inflammatory response. This multifaceted approach aligns with current understanding that gut health challenges are rarely driven by a single mechanism.

Why This Matters

When the intestinal lining is supported and the microbiome is stable, the immune system is less likely to overreact to dietary proteins. Rather than continually eliminating feeds, supporting gut integrity can help horses regain tolerance to a broader range of ingredients over time.

Take-Home Message

True feed allergies in horses do exist, but they are very rare. Most feed-related reactions are more accurately explained by intestinal barrier dysfunction and secondary immune activation. Addressing gut health first often results in more durable improvement than repeatedly eliminating feeds.

A resilient gut supports a balanced immune response—and a more tolerant horse.

References

• Bischoff, S. C., et al. (2014). Intestinal permeability—A new target for disease prevention and therapy. BMC Gastroenterology.
• Freeman, D. E., & Janecka, J. E. (2017). Gastrointestinal disease and immune interactions in the horse. Equine Veterinary Journal.
• Jackson, H. A., et al. (2003). Urticaria and allergic disease in the horse. Veterinary Dermatology.
• McKenzie, H. C., et al. (2015). Stress, cortisol, and immune function in horses. Journal of Equine Veterinary Science.
• Stewart, A. J., et al. (2017). Equine gastrointestinal barrier function and inflammation. Equine Veterinary Education.
• White, S. D. (2008). Allergic skin disease in horses. Veterinary Clinics of North America: Equine Practice.