Horse Hindgut Acidosis: Causes, Consequences, and Dietary Prevention

Hindgut acidosis occurs when excessive starch reaches the horse's large intestine, disrupting the microbial population and causing significant welfare harms including laminitis and colic.

Key Facts

Horses evolved to digest high-fiber forage in the hindgut (cecum and large colon) through microbial fermentation
When excess starch escapes small intestine digestion and reaches the hindgut, rapid fermentation by starch-fermenting bacteria produces lactic acid
Lactic acid accumulation drops hindgut pH, killing beneficial fiber-fermenting bacteria and releasing endotoxins
Consequences include colic from gas production and gut motility disruption, laminitis from endotoxin-driven lamellar inflammation, and behavioral changes
High-grain diets fed infrequently (large meals) deliver more starch to the hindgut than frequent small meals of the same total
Processing methods (micronizing, steam flaking) improve starch digestibility in the small intestine, reducing hindgut escape
The maximum starch meal threshold is approximately 1g/kg body weight - 500g for a 500kg horse - per meal
Gradual diet transitions over 2+ weeks allow hindgut microbiome to adapt to dietary changes without dysbiosis

Welfare Considerations

Hindgut acidosis creates a chain of welfare harms: immediate discomfort from gas colic, the risk of serious laminitis from endotoxin release, and the chronic behavioral changes (wood chewing, stall walking, irritability) associated with chronic low-grade hindgut dysbiosis. The welfare-protective diet for horses is primarily forage-based with careful management of starch intake when concentrates are needed for working horses. The risk is greatest in performance horses receiving large grain meals to meet energy requirements without adequate attention to starch digestibility and meal frequency. Dietary management that prevents hindgut acidosis is also preventive of laminitis - one of the most painful equine conditions - making this an area where welfare science has highly practical preventive applications.

What You Can Do

Feed concentrates in multiple small meals (maximum 1-2kg per meal) rather than one or two large feeds
Choose processed cereal grains (micronized, steam-flaked) with improved small intestinal starch digestibility
Maintain forage as the foundation of the diet - minimum 1.5% of body weight daily as forage dry matter
Implement gradual dietary transitions over 2+ weeks when changing grain types or quantities
Calculate starch per meal and stay within 1g/kg body weight maximum to reduce hindgut escape
Monitor for signs of hindgut acidosis: colic episodes, laminitis, loose feces, wood chewing, or behavioral changes after feeding
Discuss diet formulation with an equine nutritionist if your horse requires significant concentrate feeding
Consider hindgut buffers (sodium bicarbonate or commercial products) under veterinary guidance for high-performance horses at risk