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Understanding Hindgut Acidosis in Horses: Causes, Signs, and Management

Understanding Hindgut Acidosis in Horses: Causes, Signs, and Management

Introduction to the Equine Hindgut

In horses, the hindgut encompasses the cecum through to the rectum. This region is essential for fiber digestion, relying on fermentative microbial activity to convert plant fiber into usable energy. When the hindgut environment becomes too acidic, a condition known as hindgut acidosis develops, disrupting microbial balance and impairing digestion and nutrient absorption. Australia’s reliance on pasture-based feeding and selective breeding of high-fructan grasses designed for ruminants has increased the risk of grass-induced laminitis and digestive disorders in horses. Seasonal conditions such as sunny days and cool nights (common in spring and autumn), as well as drought-breaking rains, further elevate fructan levels in grasses, contributing to hindgut acidosis. 

What is Hindgut Acidosis? 

Hindgut acidosis refers to a drop in pH in the hindgut due to overproduction of lactic acid and volatile fatty acids (VFAs), which occurs when undigested starch or fructan-rich feed ferments in the hindgut. This shift kills beneficial fiber-digesting microbes and promotes the proliferation of harmful bacteria, leading to digestive upset, laminitis, and ulcers. 

Clinical and Subclinical Signs of Hindgut Acidosis 

Clinical Signs 

  • Colic (mild to severe) 
  •  Anorexia (loss of appetite) 
  •  Laminitis (founder) 
  •  Intermittent diarrhea 
  •  Stereotypic behaviors (cribbing, weaving) 
  •  Joint inflammation 
  •  Tying up (muscle disorders) 

Subclinical and Latent Signs 

  •  Decreased feed intake 
  •  Weight loss and reduced performance 
  •  Colonic ulcers 
  •  Poor feed efficiency 
  •  Dehydration, ventral edema 

 Symptoms of Colonic Ulcers 

  • Girthiness or flank sensitivity (especially right side) 
  • Tucked-up abdomen 
  • Diarrhea, difficulty collecting or bending 
  • Poor coat condition 
  • Fecal pH lower than 6.5 

Causes of Hindgut Acidosis 

  • High-Starch Diets. Overfeeding grains or rapidly fermentable carbohydrates leads to starch overflow into the hindgut. 
  • High-Fructan Pastures. Spring and autumn pastures high in fructan can trigger fermentation and acid accumulation. 
  • Stress and Medication Stress (physical or emotional) and NSAIDs can disrupt gut lining integrity and prostaglandin balance, increasing acidosis risk. Inadequate 
  • Chewing or Rapid Feeding. Poor dental health or fast consumption of food reduces proper fiber breakdown, sending large particles into the hindgut.

How Acidic is Too Acidic?

  • Ideal hindgut pH: 6.5–7.0
  • When pH drops below 6.0, fiber-digesting bacteria begin dying. 
  • A sustained pH of <5.8 damages the colon lining, reducing nutrient absorption and increasing disease risk. 

Management Strategies for Hindgut Acidosis 

1. Evaluate Risk 

  •  Assess horse history, signs, and behavior 
  •  Trial treatment for ulcers if endoscopy isn't feasible 

2. Feed Like It’s 1920 

  • Free-choice forage: Keeps the digestive system working 24/7 
  • Gradual feed changes: Avoid abrupt dietary transitions 
  • Unlimited clean water: Essential for digestion and detoxification 
  • Encourage movement: Promotes gut motility 
  • Allow social interaction: Reduces stress levels 
  • Avoid grains and simple carbs: 
  • Reduce starch load and pH drops 
  • Select low NSC oil-based feeds
  • Manage stress proactively: Trailering, isolation, training, and physical demands all contribute 

3. Dietary solutions 

  • Low Starch and Sugar (NSC) Diets: 
  • Choose grain-free diets with less than 11% NSC
  • Coconut Meal: A 100% grain-free alternative with low starch and sugar levels (NSC 11%). 
  • Supplements such as UlcaBuf to support normal hindgut pH

4. Gut Support Alternatives 

  • Prebiotics & probiotics (e.g. Saccharomyces cerevisiae): 
  • Support microbial balance.  
  • Hindgut buffers: Beet pulp, soy hulls, and products like UlcaBuf 
  • Nutrient support: B vitamins, antioxidants, and minerals for gut repair and immune health 

 Takeaway Tips for Horse Owners 

  • Hindgut acidosis is a preventable nutritional disorder 
  • Always provide ample forage and clean water 
  • Avoid abrupt feed changes and high-starch diets 
  • Replenish beneficial gut bacteria regularly 
  • Consider your horse’s background and stress levels 
  • Monitor for subtle signs, especially in high-risk horses (ex-racehorses, rescue animals)
  • Choose feeds with a balanced profile of non-NSC (oil and fibre) and NSC <12% 
  • Provide a supplement such as Ulcabuf to maintain normal hindgut pH.


Scientific Articles acid acidosis hindgut ulcers fructan probiotic low pH