Sugar in the Horse’s Diet: What we need to know

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Here we take a look at sugar in the horse’s diet and how it impacts on their health.

Sugar; a term that we all know, but probably know very little about. We dress it up with terms like non-structural carbohydrate, soluble carbohydrate etc. but it is far simpler than that, and at the same time more complex.

What is Sugar?

Sugars are a group of carbohydrates, normally five or six carbon atoms, but not exclusively in a ring formation. They can exist as separate entities such as glucose or fructose, or in combinations such as sucrose (glucose + fructose).

There are around 20 individual sugars of nutritional importance.

Added to this are isomers. Isomers are compounds with the same chemicals structure but having a slightly different arrangement, and this is the critical to the whole biochemistry of sugars.

Using glucose as an example; this exists as both an alpha and beta isomer:

Sugar - Glucose

The only difference is the positioning of the H- and OH- atoms on carbon 1. This then leads to the major divergence of carbohydrates. Sugar molecules combine through hydrogenation, the removal of a water molecule between two sugars:

sugar bonds

As can be seen, two glucose molecules, two hydrogenations but two different bonds. Where the alpha sugars combine they produce α-links, and the beta sugars give β-links.

How Sugars are Digested

Animals digest carbohydrates by their enzymes breaking the α-link and absorbing individual sugars or, possibly disaccharides, but they cannot break down the β-links. This difference splits nutritional carbohydrates; α- sides are sugars and starches, the β- are fibre.

Sugar and starch and fibre

On the sugars side (Blue) are such diverse compounds as Ribose (as in RNA) and dextrose, whilst the fibres (Green) have innumerable combinations of sugars from cellulose to gums.

All animals have the ability to digest and absorb α-carbohydrates, but rely on gut microflora to breakdown the β-carbohydrates.

Animals such as humans and pigs have the ability to process large amounts of alphas (although even for them overconsumption can lead to type II diabetes) whilst herbivores such as horses have a very limited ability; they have developed mechanisms to optimise the slow release energy of fibre.

In broad terms, whilst pigs, poultry and humans can have diets with levels in the order of 60% sugar/starch, horses should never have more than 20%, 10% if they are laminitics.

Further recommendations suggest that single meals should contain no more than 1g of sugar/starch per 1kg of bodyweight. Beyond these levels the horse is unable to digest and absorb sugars and excess passes through to the hindgut causing disruption to the microbiome.

Even within these levels there are situations where prolonged intake of the levels of alphas would reduce insulin sensitivity, interfere with normal fat metabolism and lead to a number of metabolic disorders.

Other disorders, such as Cushings where hormone dysfunction affects sugar metabolism, strengthen the need to reduce α-sugar intakes.

So, in order to maintain equine nutrition, an idea of what compromises the α-sugars, and what levels are present.

Sugar in the Horse’s Diet

The most common nutritional sugar in the horse’s diet are sucrose, fructans and starch (all alphas). They are all forms of plant storage carbohydrates, starch more specific to seeds and roots, the others to stems and leaves.

Within starch there are differences in structure between sources, but broadly speaking they are variants of α-linked glucose. It is important to realise there are different forms and sources when looking at materials.

For example, grass may be relatively low in sugars (as sucrose in the stems) at around 8% but may also contain fructans (up to 20% in spring grass) and starch in the seed heads (up to 60%) and so, depending on season, cut and maturity may vary wildly.

Again, when looking at some compound feeds, there may be a declaration of low (less than 10%) sugar or low starch, but maybe not both.

With this in mind it is useful to know what the total alpha carbohydrate content is present in various feedstuffs, including forage:

FeedstuffTotal Content % Sugars + Starch + Fructans
Spring Grass6% of fresh content 25% of dry content
Mature Grass2% of fresh content 8% of fresh content
Linseed – Whole13%
Soya – Whole12%
Sunflower – Ext8.5%

By utilising a mixture of forage, Speedi-Beet or Fibre-Beet and protein feeds (or compound that includes low alpha ingredients), it is possible to stay below those threshold levels of sugar.

Top Tips for a Low Sugar and Starch Diet

  • Research has shown that soaking hay can reduce sugar concentration.
  • Always check the bag – look to see if feeds declare they contain less than 10% sugar and starch.
  • Avoid or limit turnout when the sugars are highest (spring grass, late morning to mid-afternoon).
  • You can also help to reduce a horse or ponies intake by muzzling or strip grazing when turned out.
  • Using Speedi-Beet and Fibre-Beet is an excellent way to provide slow-release energy whilst being low in sugar and starch and are suitable for horses and ponies prone to laminitis.

By Dr Tom Shurlock, consultant nutritionist.

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