Insulin resistance Also called metabolic syndrome

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More and more horses are suffering from insulin resistance. The symptoms are controlled, but the real cause usually remains unknown. We hope this page will help change this situation.

In brief

Is this article interesting for you? We'll start by listing the symptoms so you can get an idea of whether further reading is worthwhile. Later we will go deeper into the symptoms .

  • Sensitivity to laminitis
  • Fat deposits around the mane comb ("hard neck") and tail set
  • Stubbornly over or underweight
  • Skin problems
  • Muscle fatigue, muscle pain, muscle tremors, often showing reluctance to "work"
  • Laminitis

What is Insulin Resistance?

In order to understand what insulin resistance is, we first have to look at how the carbohydrate metabolism normally functions.


Carbohydrates are the main energy supplier. Glucose is the most basic form, but stringing together glucose molecules creates the more complex carbohydrates. Many glucose molecules together form starch, even more and you have cellulose. Carbohydrates are the building blocks of the plant and are therefore a main component of the food for horses.

Carbohydrates are broken down by the digestive system into the most basic form: glucose, or "blood sugar". In that form it is transported through the blood to the cells that use the glucose as fuel. Muscles and brains are the main consumers of this fuel.


American Society of Animal Science

Glucose development after consumption of a number of foods

Supply and demand

The supply of glucose by the digestive system is of course not constant; it depends on the amount and type of food consumed. In addition, the consumption of glucose is highly dependent on all kinds of factors, including muscle activity. The more the muscles are used, the more fuel they use. However, for the proper functioning of the body it is important that the glucose level in the body remains within narrow limits. A number of mechanisms therefore continuously monitor the glucose level in the blood. Fat is used as a buffer: any excess glucose is converted into fat, and in times of scarcity the fat can be converted back into glucose.


The amount of glucose in the blood is mainly regulated by insulin. This is a hormone secreted by the pancreas (pancreas). Insulin ensures that glucose is absorbed by the cells, where it is used as fuel or converted into fat.

The more glucose is released into the blood by the digestive system, the more the cells have to absorb to keep glucose levels under control. So more glucose means more insulin.

The reverse is also true of course: as soon as the glucose level falls, because the supply stops, or because the muscles use up a lot of glucose, the conversion of glucose into fat must be stopped: The production of insulin is then reduced.


As with all complicated control systems, something can go wrong with the carbohydrate regulation. The most well-known problem with carbohydrate metabolism is "diabetes", officially called "Diabetes Mellitus", often abbreviated to "Diabetes".

Diabetes is a condition in which the blood sugar level rises too high. This can be for two reasons:

Defective insulin production
This is the best known cause of diabetes. The body cannot produce enough insulin, which causes the glucose level in the blood to rise too high. This is a situation that arises early in life and is also known as "type I diabetes". The treatment consists of making up for the deficiency by frequently adding artificial insulin by means of injections. This form of diabetes hardly occurs in horses.
Insulin resistance
With insulin resistance, enough insulin is produced, but the cells in the body no longer respond properly to the insulin; they have become insensitive to it. More and more insulin is then needed for the cells to absorb the glucose. This form of diabetes does not develop until later in life and is called "type II diabetes". In humans the term "old age sugar" is often used.

Two stages can be distinguished in insulin resistance:

  • The "pre-diabetes" stage, also called "Impaired Glucose Tolerance" (IGT). In this situation, insulin resistance is compensated by the pancreas by producing more and more insulin. The cells that have become insensitive will then still absorb enough glucose due to the increased amount of insulin. The glucose level is still within limits, but the insulin level is then considerably increased. This is the most common stage that is found in horses. With a higher supply of quickly digestible carbohydrates, there is sometimes too little insulin available, causing the sugar content to rise temporarily. The high insulin level ensures that when the glucose level falls, glucose is absorbed for too long: too much glucose is converted into fat while the glucose level assumes (too) low values. If the process of becoming less sensitive to insulin continues, it can eventually lead to the following stage:
  • Despite the high production of insulin, it is no longer possible to keep the glucose level under control. In addition, the pancreas can become exhausted and the insulin level drops again. The blood sugar level rises to high values, while the cells can no longer absorb glucose and starve. At this stage the body will lose weight. Many horses never reach this stage, but when that happens, if no treatment is given, the animal will lose weight and develop more and more ailments that eventually lead to death.


As mentioned above: In horses insulin resistance is common, mainly in the form called "Impaired Glucose Tolerance". The problem here is that the health complaints are vague and the cause is not recognized. The symptoms are treated as best as possible, but as long as the cause is not recognized, mopping with the tap remains open.


The symptoms of insulin resistance are diverse and partly depend on the individual involved. The symptoms can occur individually or together.


Own research

Robin is a pony that, despite all the good care, got laminated time and time again for no apparent cause. We therefore asked the vet to measure glucose and insulin levels. As a control, we subjected two of our own horses to exactly the same measurements. All horses were offered a normal amount of hay two hours in advance. We got the following values back from the vet:
Horse Glucose Insulin
Jack 4.1 mmol/L 9.7 mU/L
Baladeika 3.8 mmol/L 5.1 mU/L
Robin 6.6 mmol/L 41.6 mU/L
All horses have a normal glucose level. However, to maintain that glucose level, Robin needs an amount of insulin that is much higher than normal. This shows that Robin suffers from insulin resistance, entirely according to our expectations ...

Insulin resistance is something that has only recently been discovered in horses, but the link with laminitis was immediately apparent. Field and Jeffcott found that laminitic horses have less ability to process glucose (sugar) and suffer from insulin levels that are 4 times higher than normal, indicating insulin resistance.

Susceptibility to laminitis is therefore the most common symptom. The horse will become laminitis at the slightest or slightest degree. Problems with the feet are also the most common complication in people with type II diabetes. Circulation is disrupted and tissues are easily inflamed.

Despite the fact that insulin resistance and laminitis show a clear relationship, it is not yet clear exactly why this relationship exists. Dr. CC Pollit of the Veterinary Department at the University of Queensland in Australia has conducted extensive research on laminitis that has shown that laminitis is associated with altered glucose metabolism in the cells of the white line of the hoof. Another researcher, Johnson, thinks that the glucose intolerance causes changes in the blood vessels in a way that is similar to how diabetes affects human blood vessels.

In addition to the change in the glucose metabolism in the white line, the horse also becomes more sensitive to quickly digestible sugars in the diet, such as fructan in the grass. Horses with insulin resistance will therefore react much more violently to weather conditions that lead to an increased fructan content in the grass. These horses are also more likely to become laminitis from molasses in the concentrate.

You can read more about laminitis on our page about laminitis .

Weight issues


You can already deduce from the symptoms whether a horse is likely to suffer from insulin resistance. But if you really want to be sure, you can have a vet measure the glucose AND insulin levels in the blood. There are also horses that do not yet have any clearly visible symptoms, but nevertheless do have insulin resistance, so a test is very sensible for them.

Do not give food for at least four hours before the test and do not let the horse do any work for at least four hours before the test, then the test is the most reliable, but even then the results can vary significantly from day to day. Therefore, it is recommended that insulin levels are measured multiple times, according to Shannon E. Pratt, PhD, of North Carolina State University.

A value of 20-30µ/ml means that the horse has an increased value and can best be tested again in the near future (in the meantime, of course, make sure that this horse is also fed very frugally: no concentrates or grains, be careful with grass and absolutely no carrots, apples, etc.). A value of 30µ/ml indicates that the horse is truly insulin resistant. If you know that a horse suffers from insulin resistance, you can adjust the diet to minimize it.

Most horses suffering from insulin resistance are overweight. The consistently high insulin level makes it impossible to break down fat, which keeps these horses overweight, even though they are on a strict diet. It is striking that the fat is mainly concentrated at the mane comb, tail set and flanks. The "hard neck" is typical of horses suffering from insulin resistance.

This often involves a vicious circle: An insulin level that is too high ensures that fat is preserved, but the fatter the animal is, the more insulin it needs.

Underweight occurs in a minority of cases, especially in the situation where insulin resistance has reached a critical level. The cells are then barely able to absorb glucose. It is striking that the fat in the strange places (mane comb) is often retained.


Horses suffering from insulin resistance have less energy. Owners often report that it is hardly possible to get these horses "to work". Due to the consistently high insulin level, glucose cannot be released quickly enough when the muscles demand it.

Skin problems

Skin problems are also commonly reported in horses suffering from insulin resistance. Injuries heal more slowly and infections and fungal infections are more common.

How can insulin resistance develop?

Glycemic index

Oats 100
Beets 72
Maize 104
Alfalfa 52
Timothy hay 32
Bermuda hay 20
The information on this page comes from the book* "Horse Naturally" * . This book contains even more information about horse care in a more horse-oriented way.

The glycemic index is a number that expresses how quickly certain carbohydrates enter the bloodstream after consumption, and thus how much insulin is needed to process the carbohydrates.

If we set "oats" to 100, then the values of the following products are as shown opposite.

The strong increase in the number of cases of insulin resistance can easily be explained. Some causes are listed below.


Horses have become perfectly adapted to their natural diet in millions of years of evolution. We humans, however, feed the horses a little differently than what they should naturally eat, and also provide that in a different way. These differences contribute to the development of insulin resistance:

Fast carbohydrates
By nature, horses practically only eat stalky, fairly dry grass that mainly consists of longer carbohydrate chains, such as cellulose and starch. Domestic horses, however, get a completely different menu: We humans, however, feed horses concentrates and specially cultivated grass, which often contains concentrations of short carbohydrate chains. Now all carbohydrates have to be converted by the digestive system into glucose, but the time it takes for this varies per carbohydrate. Short carbohydrate chains are converted much faster than the longer carbohydrate chains that horses naturally eat. Instead of a steady stream of carbohydrates that are slowly released through the digestive system, the horse then has to deal with a sudden burst of carbohydrates that stops quite abruptly. Now insulin is a hormone, and hormones are well suited for controlling slow-moving processes. However, they have considerably more difficulty with fairly rapidly changing processes. When the carbohydrates are released from the digestive system fairly quickly, a lot of insulin must be produced in a short time. When the supply of carbohydrates suddenly ceases (because the quickly digestible sugar has run out), the insulin is still in the blood, and the cells obediently continue to absorb glucose while the glucose level is already low enough. The glucose level then varies much faster between high and low, and the extreme values are much more extreme than nature had foreseen. (See also our article on Natural Food natural food (*naturalfood) ). The main differences between a natural diet and the general usual diet are:
In this picture you can see Harisha and her foal Cameo. During pregnancy and lactation Harisha has only had grass and hay, and of course a mineral block, but no more biks, muesli, or any other additives. The result is impressive, right?
  • Concentrates
    Concentrates contain many grain products that are rich in carbohydrates but hardly contain any fiber. The carbohydrates are released very quickly, but also stop quite suddenly. Despite all the efforts of the pancreas, the blood sugar level rises rapidly at first, and then drops again very quickly a while later ...
  • Molasses
    Molasses is a frequently used ingredient in concentrates (such as mueslies) because it prevents dustiness and horses like it. The more eager horses gobble up the food, the more people prefer to buy it. Molasses, however, is a by-product of the sugar industry and consists mainly of quickly digestible sugars.
  • Grass
    The grass that we feed our horses has been specially selected for a high yield. It has also been selected for a high yield as early as possible in the year, which means that the grass must be (night) frost resistant. These types of grasses are therefore perfectly capable of producing a natural antifreeze: fructan. However, fructan is a very fast-digesting carbohydrate, and when a lot of fructan is produced by the grass (low temperatures, combined with a lot of sunshine, as often occurs in spring) then the horses get much more fast carbohydrates than what nature had foreseen. . This problem is so common that we wrote a separate page about fructan . On the fructan index index (*fructaanindex) , the amount of fructan in the grass is continuously calculated on the basis of current weather conditions.
Horses naturally eat almost continuously. The digestive system therefore supplies a continuous stream of carbohydrates. We humans, however, feed the horses portion-wise. The fluctuations in the glucose supply are now much greater than was naturally intended, and that problem is also exacerbated when we feed the horses quickly digestible food, as is unfortunately common practice.
Day and night rithm
It is a big misconception that horses have a day and night rhythm. Anyone who has ever seen horses that live outside 24 hours a day can easily find that it makes no difference to the horses whether it is day or night: they often sleep during the day, but can just as easily be eating or playing at night . We humans, however, often impose on the horses a difference between day and night: the time span between meals is longer at night than during the day, or the horses may be in the pasture during the day but have to be indoors at night, where they do not, or receive other food. This also leads to large fluctuations in the glucose supply. Furthermore, the movement that the animal receives (and thus the glucose consumption) is often different at night than during the day.

Magnesium deficiency

Recent studies have shown that a magnesium deficiency in horses is increasing. Although magnesium is a component in many dietary supplements, it does not appear to help prevent or solve a magnesium deficiency. You can read how this can be done, and how you can solve it, on our page about Magnesium .

Magnesium deficiency makes cells less sensitive to insulin. The link between insulin resistance and magnesium is so clear that many people with "adult-onset" diabetes are prescribed magnesium to make cells more sensitive to insulin. Also in horses, the administration of magnesium often appears to reduce insulin resistance. For this reason, a magnesium cure is increasingly used in the treatment of laminitic horses.

You can order magnesium chelate through our website. Read more about Magnesium (mgch) .*


Let's not get around it: Most domesticated horses and ponies are overweight. We are so used to the image of horses where the ribs are no longer visible that we have come to consider this normal.

Obesity and insulin resistance go hand-in-hand. For this reason, reducing obesity is at the top of the priority list in the treatment of human diabetics. The less "mass", the less insulin is needed.

Too little movement

Exercise is healthy and ensures a higher glucose consumption. Horses travel 30 to 50 kilometers every day in the wild, but in captivity they hardly ever get there. The less exercise, the greater the chance of disturbances in the carbohydrate metabolism.

Old age

As with humans, the risk of insulin resistance increases in horses as the years wear. On average, horses in the Netherlands do not get very old, but the horses that are not doomed to live a short life as slaughter cattle or profit point machines, on the other hand, are older than they used to be. In addition, these older horses receive more care, so that an ailment such as insulin resistance is noticed earlier.


The treatment of insulin resistance in horses is much the same as the treatment of this condition in humans. As in humans, the symptoms will never disappear completely, but the worsening can be delayed and the symptoms reduced. The points below will, especially when applied in combination, reduce the complaints:

Avoid fluctuations in glucose level. Consider the following points:
  • As with humans, "sugar" (read: "fast-digesting carbohydrates") is taboo. This includes all forms of concentrates, cereals and molasses, fruits, apples and carrots. Contrary to what the food manufacturers would have you believe: A horse needs hay, combined with a mineral block! See also our article on Natural Food natural food (*naturalfood) .
  • Provide a continuous, calm flow of carbohydrates. Try to prevent the horse from eating "by portion". Especially when a horse does not receive concentrates, he can often get unlimited hay, so that he can constantly eat small amounts. If he can't get unlimited roughage or he'll get too fat, try feeding him smaller portions as often as possible.
  • Pay attention to the weather conditions in connection with the fructan when grazing. Fructan is an easily digestible carbohydrate that is absolutely taboo for horses with insulin resistance. You can read more about this on our page about fructan . To help you determine when it is safe "grazing weather", we have created the fructan index index (*fructaanindex) , which continuously predicts the amount of fructan in the grass based on current weather conditions. It is shown in the window on the right.

When the horse continues to lose weight with a diet that consists exclusively of roughage, combined with a mineral block, you can supplement the diet with fats, such as oil. You only do this if the horse continues to lose too much weight, and therefore not as a precaution!

Because insulin resistance can be the result of a magnesium deficiency, it is recommended to give the horse a magnesium cure. Because you have to stop with concentrates and other supplements for this, this is a great time to solve any magnesium deficiency. Magnesium increases the sensitivity to insulin, so it is a good idea anyway to ensure that the horse has enough magnesium and does not consume too much calcium. You can find more about this in our article about Magnesium .
You can order magnesium chelate through our website. Read more about Magnesium (mgch) .*
Reducing any excess weight is extremely important. The lower the weight, the better the cells respond to insulin. However, the problem is that horses with insulin resistance are often difficult to induce physical activity. In addition, they appear to lose weight with difficulty, even with a very strict diet. By seeing the treatment of insulin resistance as a total package, in which nutrition, exercise and any magnesium deficiencies are addressed, it should be possible to curb obesity. Especially in this situation the following applies: better to lean than too fat!
Movement ensures consumption of glucose. The more glucose is consumed, the less glucose has to be converted into fat, and the less insulin is needed. By "moving" we do not mean "an hour's drive in the box", but rather the possibility to move continuously. So go outside 24 hours a day, both in summer and winter. To increase movement you can ensure that the facilities (food, water, shelter) are far apart, that the horse has pastures with whom it can interact socially, etc. See also our article on Housing .
Because horses with insulin resistance have a higher risk of laminitis, it is recommended to pay special attention to the hooves:
  • A lot of and regular exercise, preferably over hard surfaces, ensures good blood circulation in the hoof so that the risk of laminitis is reduced. For this reason alone, it is strongly recommended to give the horse the opportunity to move around 24 hours a day.
  • A Natural Trim is recommended because it reduces the chance of laminitis, and if it does happen, the chance of a hoofbone rotation is smallest.
  • Regularly grating the hoof wall so that it does not protrude above the sole ensures that the pressure on the hoof wall remains as low as possible.

You can read more about laminitis on our page about laminitis .

Frequently Asked Questions

Can insulin resistance cure?

Whether insulin resistance can be cured depends on the cause. If the cause was a magnesium deficiency, it can be cured. When the horse is significantly overweight, just as in human patients, the insulin resistance can disappear when the overweight is tackled. In other cases, by avoiding peaks in the glucose supply, you can reduce the insulin requirement so that the symptoms disappear.

How can I get a good magnesium preparation?

We got this question quite often; it turns out to be very difficult to get a good magnesium product. We therefore started looking for a supplier and, after much research, found a foreign manufacturer who was willing to make our magnesium chelate available. Read more about Magnesium chelate .

Where can I find more information about the best way to feed a horse with insulin resistance?

The information on this page comes from the book "Horse Naturally" . In this book you will also find a lot of information about the best way to feed a horse and how to let him move more on his own.


Many sources have been used to compile this page. We do not list them all, but limit ourselves to the most interesting:

Diabetes In Horses, Ken Marcella, DVM,

Equine Cushings and "Cushings-Like Syndrome", Melyni Worth PhD,

Glycemic index of cracked corn, oat groats and rolled barley in horses, E. Jose-Cunilleras, LE Taylor, KW Hinchcliff,

Glycemic index: overview of implications in health and disease, David JA Jenkins, Cyril WC Kendall, Livia SA Augustin, and others,

Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings, RM Hoffman, RC Boston, D. Stefanovski and others,

Mechanisms for development of laminitis, Katy Watts,

The information on this page comes from the book "Horse Naturally" . This book contains even more information about horse care in a more horse-oriented way.