Insulin Resistance by James Hart

Insulin Resistance by James Hart

Horses used to be kept for work and as economic animals they were rarely allowed to become obese. Now however most are kept for recreation and many are not given adequate exercise. Unfortunately this means that in some places we are now faced with too many obese horses. Horses in work need more feed than those that are just hanging out in the paddock and in many cases they will do just fine on grass and a bit of hay. The problems seem most common in horses that are mainly stabled but it is something we should all be aware of.
One of the more insidious effects of a lack of exercise and obesity is insulin resistance (IR). You may notice that your horse is sluggish, gains or loses weight easily and develops a cresty neck. He may also become more prone to hoof soreness and abscesses, and obesity associated laminitis. Insulin resistance is often considered with Cushing’s because some of the symptoms are similar and they are both endocrine disorders. However they are different. In all animals food is eventually broken down to glucose, a simple sugar which fuels the cells in the body. Glucose causes a normal state of elevated blood sugar (hyperglycemia), which prompts the release of insulin from the pancreas. This in turn encourages the removal of the glucose from the blood by cells which use it or store it. If a horse is insulin resistant the tissue becomes less sensitive to the action of the insulin or the amount of insulin released by the pancreas in response to high blood sugar is reduced. This leaves high levels of glucose still circulating in the blood, which continues to stimulate the pancreas to produce insulin. This in turn leads to abnormally high levels of insulin in the blood.

What Causes IR?

Little is really known about what predisposes a horse to IR but it seems likely that a genetic susceptibility is triggered by environmental or dietary factors. In humans the factors are well documented and include aging, reduced physical activity and obesity. These can trigger glucose intolerance leading to non-insulin dependant diabetes. In horses there are also a number of factors which contribute to or trigger IR. These include high carbohydrate diets, high fat diets, lack of exercise, obesity, and stress.

High-Carbohydrate Diets;

A class of carbohydrate in feeds called non-structural carbohydrates (NSC) can be a major problem. These are the sugars that plants make by photosynthesis during daylight and which may be stored or used for metabolism. Unfortunately, these levels are not listed on most feed bags and even hay can contain up to 30% NSC. There is some difference of opinion over what is regarded as a safe level and some experts feel that a horse with IR should have a total diet that is less than 10% NSC. It is difficult to achieve this level without soaking hay to leach out the sugar prior to feeding it.

High sugar levels in grass can also be a problem which is why we should avoid feeding horses on grass that has been developed specially for high producing dairy cattle. Some special culprits here are particularly the class of NSCs called fructans, which through their action in the hind gut can trigger laminitis.

High-Fat Diets;

Feeding high amounts of fat in the form of oil can be a good way to give your horse lots of calories without too much of the heating effect of grain. However once IR becomes established the ability to metabolise fat by the liver is diminished and it can be damaged. Milk thistle is a really good herb to use to help protect the liver. It can be used as an extract or raw seed, in which case it must be freshly ground. Use about 30 gms or 60ml a day.

Lack of Exercise

Horses in the wild get plenty of exercise and even keeping them in paddock should be seen as a sedentary lifestyle. Being kept in a box for most of the day is even worse. Confinement contributes to stress (see below) and lack of exercise contributes to obesity and a decrease in the in insulin sensitivity. This is why exercise is one of the main treatments for IR.


Obesity is one of the major triggers for IR. It is a simple sign that the horse has eaten more than he needs over quite a period of time. Initially when horses are fed too much for the amount of exercise they are getting the will become more excitable but over an extended period they will become obese. Excessive carbohydrate intake will increase the production of insulin, and continued exposure to high insulin levels can decrease the cells’ sensitivity to it. Obese horses also become lazy and are less likely to exercise on their own. So keeping them in a mob is better than on their own. At least they will then tend to exercise each other.


Finally stress. Horses are prey animals and if disturbed will run as their main defence. Part of this response is the release of adrenalin which causes a rush of glucose to be released into the blood stream in preparation for explosive exercise. If a horse is stressed but unable to run this will result in continually elevated blood sugar levels, high levels of insulin and over time insulin resistance.
How do I know if my horse is Insulin Resistant.

If you suspect that your horse may be IR, talk to your vet. There is a fairly simple test that compares glucose and insulin levels in the blood. Your vet will explain the results to you but it is important to remember that an IR horse may not have elevated blood sugar and can still be in the normal insulin range. It is important to look at the ratio.

Treatment Options

Horses respond well to dietary changes and there are several herbs you can use in support. The main thing to get the NSC levels down. If you have enough grass and hay this is probably the best diet. If possible test the hay. Ask your vet about where to get it done. If you can’t get the tests done it is a good idea to soak it anyway; 30 minutes in hot water or an hour in cold is all you need. Make sure you use new water each time as the sugar levels will build up in the water and there is a good chance it will start to ferment. Then you may end up with hay beer!

If your horse is in work and he needs extra feed be very careful with what you give him.

Rice bran and lucerne are fine and will give a small amount of fat. If you want to feed a prepared feed talk to your supplier about NSC levels in his feeds.

Herbs to Use

Milk Thistle is the best hepatoprotective herb we have. It is quite easy to get and has good research to demonstrate its effectiveness. It will help to prevent the build up of fat in the liver which may result in blockages.

Fenugreek is widely used as a herb to help horses gain or maintain condition. It does this by slowing glucose absorption and improving the insulin response. It contains about 50%carbohydrates, mainly in the form of a mucilaginous fibre; galactomannan. In contrast to fructan, which occurs in grass and is a NSC, galactomannan is a structural carbohydrate and much less of a problem. The research so far has been done on humans and rats so is  inconclusive in horses, but the results we have had to date have been encouraging. Further work is needed to confirm this. If you decide to use Fenugreek about 30 grams a day is the dose to use.

Globe Artichoke is another liver herb that has a hypoglycemic effect in humans. As far as we know no work has been done on horses. In the human trial individuals were given just 24 gms of artichoke powder; half in the morning and half in the afternoon. The effect was a reduction in blood sugar levels. This trial was done using artichoke flower, which is the part we use as a vegetable. The part that herbalists traditionally use is the leaf which may or may not have the same effect. Globe Artichoke leaf is also a herb that has hepatoprotective effects.

Cinnamon; Work in Japan on rats has shown that Cinnamon potentiates the effect of insulin through increasing glucose uptake; it basically has some effect against the insulin resistance by mimicking the action of insulin. Cinnamon is being used with good effect on IR horses at a dose of about 15gm a day for a 500kg horse.

Gymnema; This is another really interesting herb which is mention by some people and is included in a US product. In humans it has the remarkable effect of blocking all the sweet receptors on the tongue. It makes a spoonful of sugar taste like sand or an apple like cotton wool. As long as they have a sense of humour we often give some to people who say herbs don’t work. As long as you don’t have too much the effect wears off after 20 or 30 minutes. On a more serious level it has long been used in its native India to stabilise blood sugar levels. It slows the absorption of glucose from the intestine and inhibits the active glucose transport, but at the same time increases the amount of circulating insulin, which may not be such a good idea.


Adaptogens will help a horse deal with stress and to achieve homeostasis. The best know herbs that fall into this heading are Korean Ginseng..good but very, very expensive and Siberian Ginseng, which is not really a ginseng at all. Studies in rats have also indicated a hypogylcemic effect. These studies have not been repeatable in humans so may or may work in horses. As a general tonic however the benefits of Siberian Ginseng are considerable. A dose of 20ml a day of a 1:2 extract would be appropriate for a 500kg horse.

Insulin Resistance is a modern problem which is largely bought about by changes to the way we keep our horses and exacerbated by over-feeding and under-exercising. Although there are a number of treatments, the best are the cheapest; exercise and diet.

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