High Sugar Diet Problems for Horses

Grasses planted primarily to fatten livestock and promote milk production are ‘high sugar’ grasses. Hay made from wheat, barley, rye-grass or oats is high in sugar especially if it has been made prior to seed formation.

Sugar levels can be elevated in grasses when they are drought stressed or over-grazed. Sugar levels can sky-rocket in the spring when grass shoots away. Grains, whilst they contain some protein, are mainly carbohydrate, and therefore oats, corn, wheat and barley contribute to total sugar the horse is consuming. So does any feed containing molasses.

When the input of feed far exceeds the output required for the amount of exercise the horse is doing, problems will ensue!! What is happening is we make the mistake of thinking that grass provides enough roughage and fibre. NOT TRUE! Young, green, growing grass is mainly non-structural carbo-hydrate (sugar and starch). Clover is one-third higher in starch than grass. As the grass matures it develops more stalks and becomes more fibrous (as in roadside grass or standing hay). Then it is great as it is more fibre than sugar.

Food ingested by the horse passes through the small stomach to the ‘small intestine’ (where carbs are digested). From there it passes through to the HUGE hind-gut, (the caecum and large intestine), which takes up most of the room in the horses ‘barrel’. The hind-gut is meant to be chokka full of micro-organisms which are designed to ferment the large quantities of fibre the horse would normally eat. What happens instead is that the excess carbohydrate from the grass / molasses grains diet we force upon them, gets pushed into the hind-gut, where it cannot be digested. Resulting in acidosis (low Ph) which kills all those good micro-organisms at the same time encouraging an increase in detrimental bacteria and pathogens in the horse’s digestive system. The ensuring metabolic chaos, compounded by mineral imbalances especially high potassium, results in inflammation of the laminae of the hoof and there you have it, sore feet and laminitis.

In fact the horse/pony can eventually become insulin resistant, which is a similar condition to Type 2 Diabetes in humans.

Signs of insulin resistance include:

  • being obsessed with eating, especially grass, you can’t keep their head up!!
  • ‘lives on the smell of an oily rag’, get fat easily
  • has a ‘cresty’ neck
  • gets ‘pads’ of fat behind the shoulders and above the tail
  • puffiness, around the eyes and sheath
  • urinates a lot
  • lethargic
  • mares don’t cycle properly
  • drinks a lot
  • sore feet (pre-laminitic)
  • prone to laminitis

It is important to understand that these horses are not just fat, they have a serious metabolic disorder that needs urgent action! They are like diabetic people and suffer from the dysfunction of every major organ system in their body, the circulatory system (especially to the hooves), the digestive system (especially the hind-gut), the reproductive system, the nervous system (including the brain), the endocrine system. They are an inch away from foundering.


These symptoms can be reversed by removing the horse from anything green (especially short grass in spring and autumn, merely restricting grass may not be enough), and feeding plenty of hay that has had the much of its sugar content leached out by soaking in a tub of cold water for at least an hour before feeding. The water goes brown and fizzy. Tip it on your garden. Supplementation with a quality Vitamin & Mineral supplement containing organic chromium and magnesium. Attention to healthy hoof form and as much exercise as possible are equally important.


Please understand that it is primarily a hind-gut problem caused by sugar overload, lack of fibre and lack of exercise. These horses are the equivalent of the couch potato person who lives on junk food.

The key to a healthy horse with healthy hooves is to look after the flora in the hind-gut by ensuring the majority of the horses diet consists of coarse fibrous material such as mature grass, hay, chaffs and beet.

Fibre Requirements Relative to Lifestyle
(Adult Horses & Ponies)










  • Soak hay in water for one hour (to reduce sugar content) discard water and feed immediately.
  • Feed Hay without any perennial rye grass, clover or any of the other ‘Bad Grasses’.
  • Supplement with calcium and magnesium if grazing oxalate grasses.
  • Supplement with extra calcium, magnesium & sodium if grazing rapidly growing grasses especially in cool, wet, cloudy, frosty climatic conditions. The first shoots to appear after a drought breaking rain will be particularly dangerous.
  • Supplement with sodium to help correct the sodium: potassium ratio and help buffer any acid build up, to increase water intake (there must always have fresh drinking water freely available).
  • After approx 6-9 months the obese/laminitic horses’ metabolism will be returning to normal and they can be fed as ‘Idle’ Be extremely diligent about not allowing a relapse.
  • When on any kind of pasture feed a toxin binder containing natural yeast cell wall extract (ToxDefy). For oxalate pastures in particular a highly absorbable calcium and magnesium supplement such as XtraCal or GrazeEzy is ideal.
  • For horses in moderate to intense work add carbohydrate (e.g. grass & grain) and protein (e.g. soya bean meal, solvent extracted canola meal, sunflower seeds ) according to energy requirements (refer to table above). Be careful of full fat soy in warm weather as the oil content may go rancid.
  • Avoid sugar and protein overload in broodmares, young & growing horses, by supplementing their diet with enough high fibre intake to offset the high sugar content of lush pastures.

Why Add Fibre?

Adding fibre to the diet of Aust & NZ pasture-fed horses is vital:

  • It keeps the hind-gut and its resident micro-organisms healthy, preventing sugar overload, which causes hind-gut acidosis (sloppy manure), ADD (attention deficit disorder), insulin resistance, metabolic chaos, laminitis.
  • The digestion of fibre has immune-boosting, anti-allergic and hormone regulating effects.
  • The fermentation of structural fibre is a major source of energy.
  • Fibre helps synthesise B-Vits & Vit K for calmness and good health.
  • Provides fuel for their internal body heater.
  • Creates a water reservoir for proper hydration, especially after sweating, urinating and salivating.
  • Requires more chewing = more saliva, preventing stomach ulcers.

Does your horse eat Grass? Clovers?

Molasses feeds? Grains?

Consumption of these, without sufficient accompanying fibre according to lifestyle will sooner or later result in a vast array of ill-health problems. Symptoms including many of those in the above list, (pg 5-6 e.g. herd-bound, nappy), ravenous appetites, insulin resistance, obesity or ill-thrift, weak, sore feet and laminitis will become apparent.

Green grass which is kept at a young stage of growth by constant grazing does not supply enough fibre in the diet of Aust & NZ pasture fed horses.

How Much Fibre?

A 500kg horse requires approximately 2% of his bodyweight per day. i.e. 10 kgs /day, 365 days/yr. Hay bales vary but this is approximately ½ bale. This can be achieved with a combination of hay, chaffs and beet pulp.

NB. A heavy Hack of 16.2 hands will weigh approximately 550kg, a 14.2 galloway approximately 400kg and a 12.2 pony will weigh approximately 300kg. Take empty float to a weigh station, then take horse in float to weigh station, this will give you an accurate weight. Alternatively use a weight tape.

If the horse is light in condition feed according to the weight he should be, not the weight he currently is.

If you want your horse to lose weight, soak the sugar out of the hay rather than cutting down his hay. Horses have a need to be eating and chewing 16-18 hours a day. Long periods without food cause mental stress and stomach ulcers.

B-Vitamin Deficiency is Caused by a Lack of Fibre

Within the large intestine of the horse, there should be a healthy population of ‘good’ bacteria, whose purpose it is to breakdown the food further, producing energy-rich, short-chain fatty acids. These bacteria also produce essential B- vitamins of which biotin is one and vitamin K necessary for just about every function in the body, including healthy red blood cells and optimal function of the nervous system, healthy hair coat and strong hooves.

Signs that a horse is not making sufficient of his own B vitamins are poor appetite, sour attitude, anaemia, poor hooves and skin conditions.

Biotin is one of this large group of vitamins. Everyone is busy supplementing with biotin to improve hooves when all the horse needs is more fibre in his diet so he can make his own. Hooves will not be strong and healthy on a sugar diet!!

Anything that upsets digestion, such as a low roughage diet, (e.g., spring-time sloppy manures caused by acidosis) or increased stress of any kind, will interfere with the horses ability to produce his own B vitamins.

It is a good idea to make sure your multi vitamin/mineral supplement has the full range of B-Vitamins. The range of Vitamin B’s are water soluble and not stored in the body, you cannot overdose on them.

Selenium is essential to good health in the horse. It is a trace mineral which helps to make important antioxidant enzymes that have several functions in the horse’s metabolism. These selenium containing enzymes provide antioxidant protection in every cell of the horse’s body. They also have roles that affect growth, immune function, muscle recovery and reproduction.

Many areas of New Zealand and Australia have soils deficient in selenium, which means unless you are supplementing with it, your horse is likely to be deficient. Too little selenium in the diet is a problem, it’s a bit like trying to run a car without oil, causing degeneration of muscle tissue, stiffness of gait and a predisposition to ‘tying up’. However, too much selenium is a problem as it is toxic to your horse. This has become more of a possibility since selenium is now added to a lot of feeds.

Annual blood tests are essential, so you know exactly how much to supplement with.

It is best fed in small doses often, as in the organic forms available that you add to a daily feed.

by Jenny Paterson B.Sc (New Zealand)

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