If Maartje could pick one subject she wishes more people knew about, it would be fibre. In this episode she covers a common problem: too much sugar and starch in one go.

Short answer

A horse has only limited capacity to digest sugar and starch: the organs involved are relatively small, feed passes through quickly and enzyme production is low. Whatever is not digested in the small intestine reaches the caecum and large intestine, where it is fermented. That can cause colic, laminitis and reduced immunity.

Why can a horse only handle a small amount of starch?

Three things come together.

1. The organs are relatively small. The stomach of a 500 kg horse holds roughly 8 to 15 litres – small for an animal of that size.
2. Feed passes through quickly. Feed spends little time in the small intestine, which leaves limited opportunity for enzymatic digestion.
3. Enzyme production is limited. Production of amylase, the enzyme that breaks down starch, is particularly low in horses.

The result: part of the starch never leaves the small intestine as digested sugar. It flows straight on.

What happens when sugar and starch reach the hindgut?

In the caecum and large intestine, that sugar and starch is fermented – much like fibre, but far faster. The pH drops. The fibre-digesting bacteria that belong there do not thrive in an acidic environment.

That can lead to several problems:

• colic
• laminitis
• reduced immunity

Research in Belgian horses showed that a high intake of sugar and starch, a low number of meals per day and a low forage intake were associated with a higher risk of gastric ulcers.

Solution 1: split the feed into several small portions

Feeding products high in sugar and starch? Spread them over several small portions a day rather than one or two large ones. That gives the small intestine a chance to do its job, and less undigested starch ends up in the hindgut.

In practice:

• three or four small portions beat two large ones
• never increase in one step – build changes up over at least two weeks
• look at the starch content on the label, not only at the quantity in the scoop

Solution 2: build the ration on fibre – including for sport horses

There is a persistent idea that a horse with a high energy requirement simply has to have concentrate. That is often not true. Horses with higher requirements, sport horses included, can be fed very well on a fibre-based ration.

Think of highly nutritious forage such as Hartog Lucerne Pellets. That lets you raise the energy density of the ration without raising the sugar and starch load.

The principle is straightforward: change the energy source, not the amount of feed the horse has to process at once.

Frequently asked questions

How much starch can a horse have per meal? A widely used practical guideline is a maximum of roughly 1-2 gram of starch per kilo of bodyweight per meal. For a 600 kg horse that works out at approximately 600-1200 grams of starch per feed. Always calculate using the figures on your own product’s label.

What is hindgut acidosis? Acidification of the hindgut caused by rapidly fermentable carbohydrates arriving there. The pH drops, fibre-digesting bacteria disappear and endotoxins are released.

Would I recognise this in my horse? Not always straight away. Vague signals include loose droppings, recurring mild colic, sensitivity in the flank, or a horse that becomes sharper after a feed change. If you remain in doubt, speak to your vet.

Sources

• Galinelli N. et al. (2021), High intake of sugars and starch, low number of meals and low roughage intake are associated with EGUS in a Belgian cohort, J Anim Physiol Anim Nutr: https://onlinelibrary.wiley.com/doi/10.1111/jpn.13215
• Sykes B.W. et al. (2015), ECEIM Consensus Statement – Equine Gastric Ulcer Syndrome in Adult Horses, JVIM: https://onlinelibrary.wiley.com/doi/10.1111/jvim.13578
• Merck Veterinary Manual – Nutritional Requirements of Horses and Other Equids: https://www.merckvetmanual.com/management-and-nutrition/nutrition-horses/nutritional-requirements-of-horses-and-other-equids