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The modern horse still has its ancestors’ gut design – that of a fibre-digesting herbivore. This means that two-thirds of the digestive tract is devoted to fibre digestion through fermentation, while just one-fifth is designed to process starch from cereals, oil and protein.

For horses in light work, feeding regimes match digestive design, as most of the diet is forage. However, for working horses, low-energy forage does not provide sufficient energy and cereals or oil are added to make up the shortfall in energy.

Levels of starch in the diet must be limited to prevent undigested materialpassing through to the hindgut, which is not designed to digest starch. Potential problems caused by starch passing into the hindgut include colic, excitable behaviour and changes in temperament.

Fibre as an energy source

Fibre can provide the horse with energy, as well playing an important role as a filler. Made up of a complex of carbohydrates and compounds, it is broken down by bacterial fermentation in the hindgut.

Fibre is made up of lignin, cellulose and hemicellulose. Lignin is indigestible, and feedstuff with high lignin levels, such as straw and mature seed hay, will have a low energy content and is great for filling a horse up.

Cellulose and hemicellulose are digested by bacteria in the hindgut. The higher the levels of cellulose and hemicellulose the more energy the forage has to offer.

Importance of fibre

Fibre should be at a maximum in the diet of the following cases:

  • All horses, but particularly those fed a low-energy feed
  • Horses requiring stamina. Another facet of fibre digestion is that the energy is slow release, capable of sustaining work for a long period. Good for hunters and endurance horses
  • Horses with loose droppings – often a good indication ofa reduction of long fibre in the diet
  • Those prone to laminitis, colic and tying up – these problems can all be related to disruptions in fibre supply
  • Haylage diets; if you are controlling the amount offered this means forage fibre levels will be low
  • When grass quantity drops. Particularly relevant during hot summer and winter. As soon as grass growth slows, a horse eats less fibre each day.