Sugar in the Diet - Friend or Foe?

Sugar gets a lot of bad press but is actually a very natural part of the horse’s diet.  Grass, for example, can contain as much as 20-40% so a 500kg horse grazing summer pasture will consume 10kg dry matter per day, of which at least 2-2.5kg will be sugars!  Fructans in grass are made up of simple sugars, as is starch from cereals, and all forms are broken down to glucose, the simplest sugar, which is used as the primary energy source for body tissues, from the brain to the muscles.

Sugar is a broad term for range of simple carbohydrates made up of one or two molecules (mono or di-saccharides) found in feed.  Glucose is the most important monosaccharide and most dietary carbohydrates, like starch, are broken down through digestion, into glucose molecules.  Starch is the form in which glucose is stored in grains (seeds) to support germination, while fructan is the form in which the plant stores sugar in its leaves for survival.

So sugar is an essential element of the diet and easily digested by the horse, with simple sugars and starch being broken down and absorbed in the small intestine and fructans fermented in the large intestine (hindgut).  Sticking to the rules of feeding, and keeping meal sizes small, will help support this efficient digestive process but overloading the system can cause problems.

For horses prone to nutrition-related disorders, like laminitis, controlling sugar intake is not the complete answer, rather total carbohydrate intake (sugars, starch, fructans etc) should be restricted.  “Low sugar” feeds may help but only as part of an overall feed and management programme. 

This also applies to those exhibiting Equine Metabolic Syndrome (EMS), which gives rise to insulin resistance and a subsequent inability to control the level of glucose in the blood.  EMS is associated with excess body fat and, as a rule the symptoms can be reversed by a return to a healthy body condition.  This will mean a reduction in total dietary carbohydrate ie. a reduction in calorie intake, coupled, where possible, with an increase in exercise to encourage weight loss.

Other sources of dietary sugar include, hay (around 10%) and apples and carrots (as much as 50%), sugar lumps and “Polos” (100%), while coarse mixes may contain 10 – 12% sugar.  As an ingredient, molasses often gets the blame for contributing “too much sugar”; it actually rarely contains more than 40-50% sugar and, with an inclusion rate in feeds of less than 10%, makes a minimal contribution to the overall diet.

Even “molasses-free” feeds will contain sugar that is naturally occurring in the ingredients – straw and alfalfa contain sugar, just like grass, hay and haylage, so “sugar-free” feeds are nigh on an impossibility.  Indeed, the bulk of the sugar in any horse’s diet will be coming from his forage and, without laboratory analysis, levels can be hard to assess.  For those on a “reduced sugar/calorie” diet, soaking hay or haylage will help to “wash out” water soluble carbohydrates, including sugars, but this again is hard to quantify.

Quoting the sugar content of feeds is not a requirement for manufacturers but, when appropriate, many will give levels on their web sites or product literature.  As already discussed, these values should not be taken in isolation and, for those with clinical reasons for controlled sugar intake, it is the overall diet which should be monitored rather than one particular element.

In mammals, the storage form of glucose is glycogen and this is stored in the muscles to fuel them during work.  After hard work, these stores can be depleted or even exhausted and will need replenishing from the diet.  Research has shown that feeding compound feed, alongside forage, helps to restore muscle glycogen levels quicker than with hay alone and that feeding 1.5 hours after exercise was more effective than delaying for 4 hours.  This can present a dilemma for performance horses on a low starch diet to help control the incidence of gastric ulcers as, with the reduced level of readily available glucose from starch, recovery from exertion may take longer.

So it’s evident that, as for humans, it’s a case of everything in moderation.  Sugar, in its various forms, is a dietary friend as long as it is not consumed to excess or too much in one go.  Whilst its control is key to the management of certain clinical conditions, a sensible approach to achieving both a balanced diet and ensuring sufficient exercise, should help avoid some of these situations arising in the first place.