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Why Insulin Resistance is often mistaken for sweet itch

Has your horse been rubbing as a response to gnats or sugars? Summertime itching tends to be ascribed to sweet itch. However, a lot of these horses don’t have sweet itch at all, but are suffering from Insulin Resistance instead. Both conditions have a lot of overlap in terms of their symptoms, but they have different causes and require their own specific treatment. Can you tell the difference between Insulin Resistance (IR) and sweet itch? Since Insulin Resistance is not as well known, we will first address this condition followed by a comparison with sweet itch.

How to recognise Insulin Resistance in your horse?

The most obvious symptoms of Insulin Resistance in horses are hardened and thickened manes, often combined with wrinkles. Horses will often rub their manes as a result of the irritation. In addition, mosquitoes tend to be drawn to horses with Insulin Resistance, possibly due to the fact that their blood tastes sweeter and their immune systems are weaker.

Other symptoms of IR are fat accumulation near the tail root and fat lumps behind the shoulder blade. Mares also tend to have a thickening near the navel and geldings (more common than in stallions) tend to have a swollen sheath.

Insulin Resistant horses are often stiff and have reduced mobility. The muscles are hardened and unworkable. But the biggest problem with IR is laminitis. The large amounts of sugar processed in the intestines change the intestinal flora, causing a release in the intestinal wall (basal membrane) and of enzymes into the blood. The bloodstream then distributes these enzymes throughout the body, causing this release process to occur in other places, including the basal membrane in the hoof. In addition, fat accumulation throughout the body means that horses suffering from IR will have reduced blood flow in the legs which gives rise to laminitis.

Sugars in the body

Before getting into what Insulin Resistance is, it is a good idea to first address how a horse’s body deals with and processes sugars. There are two types of carbohydrates that a horse ingests through its food:

  • Soluble carbohydrates (sugar and starch): these can be broken down and absorbed by the small intestine and provide the horse with a quick source of energy. An excess of these carbs causes indigestible carbohydrates to enter the colon where they disrupt the intestinal flora.
  • Complex carbohydrates (fibres): these are processed in the colon, with the help of bacteria. This releases volatile fatty acids, which the horse can use as a slow, continuous source of energy.

The sugar is absorbed into the blood through the intestines and transported to all the organs.

How is blood sugar regulated?

The pituitary gland, an organ near the brain, regulates the blood sugar balance. The pituitary gland measures the blood sugar level as well as the amount of insulin in the blood. It controls other organs, thereby ensuring a stable blood sugar level. For example, the pituitary gland controls the pancreas which is where insulin is made. Insulin is a hormone. Its primary function is to transport glucose from the blood through the cell walls (using insulin receptors) into the cell, where the glucose is either used as fuel (energy) or stored as fat.

The pituitary gland and pancreas are intimately connected through a feedback system of receptors. This system notifies the body whether more insulin is required to lower the blood sugar level or more fat needs to be converted to glucose (gluconeogenesis) to be used as fuel by the cell.

The more sugars the food contains, the more insulin it takes to balance the blood sugar level. That is where things can go wrong.

What is Insulin Resistance?

In the case of Insulin Resistance, a change in the cell wall structure diminishes the insulin receptors’ response to the insulin. As a result, more and more insulin is required to transport glucose through the cell wall and the pancreas goes into overdrive to meet the body’s insulin demand. Once the glucose uptake has changed as a result of the Insulin Resistance, the feedback mechanism is compromised. This causes the cells to keep storing the glucose as fat and severely reduces the rate at which glucose can be burnt to fuel exercise. Because the insulin receptor functionality has been reduced, it is more difficult for new glucose to enter the cells, rendering the horse stiff and slow.

What are the consequences of Insulin Resistance?

Insulin Resistance isn’t always properly diagnosed since it comes with a wide range of potential symptoms. The most common symptoms are hardened manes and accumulation of fat near the manes, tail root and belly. But horses can also develop laminitis and tie-up as a result of IR. In addition, arthritis symptoms tend to exacerbate and they tend to develop sore backs and muscle stiffness. Horses with IR are usually overweight (or will develop obesity), but underweight may be a symptom as well. Horses with IR are also more prone to inflammations. IR causes fat to be stored throughout the body which results in increased cytokine release (a protein involved in inflammation promotion, among other things) which exacerbates the horse’s inflammation sensitivity.

What causes Insulin Resistance?

The main causes of Insulin Resistance are diet, stress, infection and hormonal issues in mares. Diet is the most common culprit. Horses aren’t built to process large amounts of sugar, which disrupts their intestinal flora. Concentrate that is high in sugar (or carbohydrates) or rich grass/hay can cause sugar spikes that the horse is unable to process. When the horse consistently gets a large quantity of sugar in its diet, it will have to generate more and more insulin, depleting the pancreas and rendering the horse insulin resistant. Not all horses will develop these symptoms right away, but cold bloods (Icelanders, Fjords, etc.) are much more sensitive in this respect. It is important to make sure you horses get enough vitamins and minerals. Any deficits in this regard can also contribute to Insulin Resistance.

(Extended) stress can cause Insulin Resistance as well. Stress hormones (adrenalin and cortisol) require cells to burn fuel quickly to ready the body for a flight response. If this process is always present in the body (e.g. due to remaining stabled for a long time or a lack of peers), the body’s balance is disrupted which can lead to IR.

But an intestinal infection or an acute infection in a leg or the airways can contribute to IR as well. In the case of an intestinal infection, the intestinal flora is disrupted which can lead to disrupted glucose uptake and processing. Mares that get hormones for an extended period of time to regulate their reproductive cycle, are at risk of developing IR as well. Mares that fail to go into heat may be IR as a result of disruption of the hormones regulated by the pituitary gland.

How to tackle Insulin Resistance?

It is important to analyse your horse’s diet. Reduce its sugar intake as follows:

  • Use low-sugar concentrate (or replace it with a balancer)
  • Use low-sugar roughage and/or low-quality grass (lots of herbs, unfertilized and bolted)
  • Keep an eye on the fructan index and do not let your horse graze if the fructan level is too high
  • Add cannabinoids extracted from cloves to support the endocannabinoid system (ECS system) and the high therapeutical anti-inflammatory effect. The ECS system Is the signaling device of the body and checks at the cell level whether there are abnormalities. In case of deviations, it sends a signal to the brain so that the brain can send the right auxiliary substances. This balances the body, also the sugar and hormone levels.
  • Add Omega 3 because of its anti-inflammatory effect (e.g. salmon oil)
  • Add magnesium
  • Reduce stress

Some Insulin Resistant horses become lethargic, lacking energy and drive. It is a pitfall to increase these horses’ concentrate intake. The sugars found in this type of food will only exacerbate the problem. You can help these horses by adding a fatty energy source and (usually) by having them lose weight.

Attention! In the event of extreme drought or low-quality soil, the grass may get stressed which causes it to produce more sugar to protect itself. Make sure the grassland that harbours your horse is suitable. Have the land analysed if you aren’t sure.

What is the link between sweet itch and Insulin Resistance?

There is no link, and yet there is! A horse that is overly sensitive to gnat bites (more specifically, to the saliva that is left behind after a bite) doesn’t necessarily have to be Insulin Resistant. These horses have an allergic reaction to the insect bites which causes an itch. In the case of sweet itch, the skin contains elevated quantities of inflammation-promoting substances that lead to an itch response as soon as they get into contact with the protein in the saliva of the culicoides midge.

On the other hand, horses with Insulin Resistance can develop sweet itch. The fat accumulation around the tail and manes causes irritation (and elevated amounts of inflammation-promoting substances) and the immune system of IR horses is weakened as well. Because the horse begins to rub, the skin is damaged which exacerbates the inflammatory response as well as the horse’s allergic reaction. In short, sweet itch can be triggered by Insulin Resistance. Click here to learn all about combating sweet itch.


Insulin Resistance and Sweet itch are two distinct conditions. However, some of their symptoms overlap which often causes Insulin Resistance to be misdiagnosed as sweet itch.

Insulin Resistance causes depletion of the pancreas due to (constant) excessive sugar intake. As a result, more and more insulin is required to transport glucose into a cell. In addition, the body enters a mode where most of the glucose is being stored as fat. This causes the characteristic accumulations of fat near the manes and the base of the tail. These fat accumulations lead to itching and make the horse extra appealing to gnats. Hence the frequent mix-up with sweet itch. So, Insulin Resistance is not the same thing as sweet itch, but sweet itch can be triggered by Insulin Resistance. Are you unsure whether your horse has sweet itch or Insulin Resistance? Have your vet perform a blood test to check for Insulin Resistance.

Whichever condition your horse turns out have, it is always a good idea to limit the sugar intake. It is very important to keep an eye on the fructan index in summertime if your Insulin Resistant horse is out in the field. An elevated fructan index means the grass contains a lot of sugar which is dangerous to IR horses.

Did you know that magnesium plays an important role in stabilising insulin receptors, regulating inflammation processes in subdermal fat and stabilising the cell wall? This is why Insulin Resistant horses are often treated with magnesium. Also cannabinoids extracted from cloves are very helpful to increase the healing power of the body itself.

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