What Is Hindgut Acidosis?

Hindgut acidosis is an increase in acidity of the horse’s hindgut (the caecum, large colon, small colon and rectum). This decrease in pH is often caused by the fermentation of starch in the hindgut, which also results in an increase in amylolytic microbes, which ferment starch, and a decrease in fibrolytic microbes, which ferment fibre. These changes in microbial population, increased starch fermentation in the hindgut and the byproducts this produces, including lactic acid, leads to a change in the hindguts pH.

The ideal pH for the horse’s hindgut is between 6.5-7.0

Hindgut acidosis can occur when horses are fed excessive starch in their diets. It is recommended that the safe upper limit of starch intake for a horse per day is 2g/kg body weight (Julliand et al., 2006), and the recommended intake per meal is 1g/kg body weight. When horses consume too high a quantity of starch at once, it cannot always all be digested by amylase in the small intestine as it should be. It is found that the excess starch escapes enzymatic digestion and can end up being fermented in the hindgut.

Common clinical signs of hindgut acidosis include –

• Decrease appetite
• Decrease in performance
• Symptoms of colic
• Stereotypic behaviours
• Tying- up
• Loose droppings
• Horses suffering from hindgut acidosis may also be at a higher risk of developing laminitis, due to the toxins released from the death of the fibrolytic microbes due to the fermentation of starch in the hindgut
• Hindgut acidosis has also been shown to link to the development of hindgut ulcers

Minimising the risk -

Feed and starch quantities -

As owners, it is important to be aware of the quantity of starch we are feeding our horses per meal. It is recommended that horses do not consumer more than 500g per 100kg BW and 1g of starch per kg BW per meal.

Feeding horses little and often –

by offering smaller, more frequent meals rather than fewer, bulkier meals we can encourage a more natural feeding routine for our horses who have evolved to be trickle feeders. This will also reduce the quantity of starch ingested at once to reduce the risk of excess starch moving into the hindgut and being fermented.

Promoting pH balance-

Feeds containing an acid buf, such as Saracens Shape-Up, Competition-Fit Balancer, Condition-Improver Cubes, Condition-Improver Mix Re-Leve Mix and Equi-Jewel, help to maintain an optimum pH in the hindgut, and may also help combat any fluctuations caused by the fermentation of starch and the onset of hindgut acidosis.