Insulin resistance in horses

The current horse is a legacy of 4 billion years of evolution. Genes adapt very slowly, with the result that we currently live with genetic information from 30,000 to 40,000 years ago. The nutrition and management of the horse have changed considerably in recent years. The conflict between the ancient genome and the health management of the current horse sometimes causes problems. Insulin resistance is an example of this.

What Is Insulin Resistance?

Insulin is a hormone produced in the pancreas. The main function of insulin is to transport glucose from the blood through the cell wall into the cell with the help of so-called insulin receptors on the cell walls. Once in the cell, glucose can be burned to perform work (for example in the muscles or the brain), or to be stored (fat). The more glucose is offered through the diet (all carbohydrates from the diet are broken down into glucose), the faster the body is inclined to store this glucose in the form of fat, as a reserve for bad times.

The blood sugar level must stay within certain limits because too high or too low blood sugar can lead to many health problems. When there is (too) much glucose in the diet, more and more insulin is needed to regulate this process.

Insulin resistance changes the receptors on the cell wall. The lipid structure of the cell wall changes, causing the insulin receptors to respond much less well to the insulin. As a result, more and more insulin is needed to transport the glucose through the cell wall. In the first instance, insulin resistance is not yet a real diabetes, as is often thought. The pancreas or pancreas is still functioning, but works overtime to meet the high need for insulin. This overtime can lead to real diabetes (almost never in horses, but often in humans), because the pancreas eventually gives up. Until then, the process can still be reversed to a certain extent.

It is also vital for animals to regulate the blood sugar level in the blood within certain limits. This is a collaboration between the pituitary gland, the pancreas and other hormone glands that are controlled by the pituitary gland.

The pituitary is the controller that works just like a thermostat. When the temperature in the room has reached the correct height, the thermostat switches off until it registers a temperature that is too low and switches on again to ensure a constant temperature via a feedback system. By measuring the blood sugar level and the amounts of hormones in the blood flowing through the pituitary gland, the constant composition of the blood sugar level is monitored. This is adjusted if the circumstances require it, such as during work, stress or rest where more or less glucose is needed. This is also a feedback system. The system can also register that the blood sugar level is too low, the counterpart of the storage of glucose, the gluconeogenesis, triggered by other hormones. In gluconeogenesis, stored fat is converted back into glucose that can be burned in the cell to do work.

When glucose uptake has changed due to insulin resistance, the feedback system no longer functions properly. Due to the high insulin content, the storage of glucose as fat in the cell also continues: the button gets stuck on ‘save’. If work is then carried out and glucose has to be burned, the combustion process starts much too slowly. In addition, the newly formed glucose is very difficult to enter the muscle cells due to the slow action of the insulin receptors. The result of this is slowness and stiffness in movement.

Causes of Insulin Resistance

  1. Nutrition
  2. Stress
  3. Inflammation
  4. Hormonal problems in the mare

1: Nutrition

From the above it is immediately apparent that nutrition plays an important role in the development of insulin resistance; it is the most common cause. The nutrition story has many more facets than just the development of insulin resistance, too many to be discussed in detail here.

An excess of ‘fast sugars ‘is in any case not good. Most horse food is pressed with molasses and is, by definition, not good for a horse that is sensitive to insulin resistance. Sugar- and energy-rich sports food and muesli flavored with molasses are also not good for the insulin-resistant horse. Unfortunately, a mistake is regularly made: ‘my horse is slow, stiff and tired quickly, so let me put in energy-rich concentrates’. This is counterproductive and ultimately makes the animal sicker.

A large number of boarding stables have also arisen from a cattle farm with cows. Here the meadows are sown with English ryegra s . This grass has short stems and contains a lot of fructan and is fertilized regularly. It is an excellent product for good milk production in cows and for creating beautiful, tight green pastures, but it is too rich for horses. Horses need a ration with one constant, slow supply of glucose from the intestine as is the case with long-stemmed grass and herbs. Horses do not tolerate the peak, enormous supply of glucose as they get with two large feedings a day and sugary grass. The hormones have to react too quickly to this, so that they cannot properly regulate the absorption. The intestinal flora present shifts from bacteria that can digest cellulose quietly and slowly (the hard layer around the plant) to bacteria that have a much faster metabolism and are happy with those fast sugars. The slow bacteria that the horse has adapted to are displaced from the intestine, this causes far-reaching changes within the intestine.

Fortunately, this does not happen to the same extent for all horses, it also depends on the type of horse. For more information about different horse types, please visit So-called ‘earth horses’ are more sensitive, as are the types of wood when they cannot do enough work. Or breeds such as Icelander, Shetland ponies and Fjords, which are sober by nature and do not need enough. These breeds were born to do hard work or survive in the cold on little food. These animals are naturally set to store their reserves to save energy for the bad times. However, these bad times will no longer come under the current Dutch circumstances. The thousands of years of survival in austere, sometimes hostile habitats have determined the genetic background of these horses. It will also be thousands of years before the premise of ‘excess’ changes their genome.

These are just a few of all aspects of diet as a cause of insulin resistance and the management mistakes made with the best will in the world. In the context of nutrition, it should be mentioned that deficiencies of certain minerals in the diet, such as magnesium, can also contribute to the development or maintenance of insulin resistance.

2: Stress

To regulate stress, the body produces hormones such as cortisol and adrenaline. These stress hormones have an important function in regulating combustion in the cell. These hormones are also influenced by the function of the pituitary gland.

Although hormone feedback systems are never simple, here is a simple example. Stress promotes, especially in horses, the fright, fight and flight reflex. Rapid combustion is necessary to be able to flee or fight (to provide labor). Among other things, the previously mentioned stress hormones such as adrenaline and cortisol play a role in this. These hormones have an influence on gluconeogenesis and combustion and storage.

In our opinion, a horse that is stabled all day is at rest. This is the case with some horses, but not by all. Horses that hear and see nothing are sometimes in a constant state of stress. Certain hormones are produced too much and the balance is disrupted. These hormones have many more functions in the body and if they are always in excess, it will also go wrong at other levels. This constant state of overstimulation also depletes the calcium and magnesium balance inside and outside the cell because the animal is, in fact, constantly ready to flee. Other causes of stress are the lack of contact with other people, being indoors frequently and not getting enough sunlight, a lack of exercise and improper treatment and treatment.

Magnesium plays an important role in stabilizing insulin receptors, regulating inflammatory processes in the subcutaneous fat and stabilizing the cell wall. There is often too little magnesium in the diet. In a stress-sensitive horse, the stock is used up even faster. Thus, there is a diversity of events that can contribute to imbalance causing or exacerbating insulin resistance.

3: Infection

A chronic infection, especially in the gut, or an acute infection in the respiratory tract or in the leg, can contribute to the development or exacerbation of insulin resistance. As a result, the horse can become laminitis while nothing in the daily routine has changed. The hormones involved in regulating the infection, such as cortisol, also play a role here. An infection of the intestine disrupts the intestinal flora even more than the diet already did, which can also lead to a worsening of insulin resistance.

4: Hormonal problems in the mare

The influence of estrogens in the mare with abnormal heat ability can also contribute to the development or worsening of insulin resistance. These hormones are regulated by the pituitary gland and with a constant disruption of estrogen levels in particular, the hormone balance can become disrupted. This often works the other way around: if a mare is very insulin resistant, she will show little or no stallion. A mare on long-term estrogen preparations will be able to develop insulin resistance as a result of these drugs.

Consequences of insulin resistance in the horse

When a horse is insulin resistant, it often does not stop with this complaint itself. Insulin resistance in turn (partly) causes a variety of physical problems in the horse.

Diseases and complaints:

  • overweight or underweight
  • fat accumulation around mane and tail set and belly fat
  • laminitis – skin problems such as eczema
  • fatigue, muscle pain, muscle tremors and muscle tension
  • reluctance to work
  • reduced fertility
  • respiratory problems
  • Cushing
  • worsening of complaints such as arthritis
  • back pain

Measurable and visible changes:

It is important for you and for the veterinarian to recognize an insulin resistant horse, preferably before actual complaints have arisen. The most recognizable is the thickening and hardening of the mane comb. Often wrinkles also appear in the skin. There are fat deposits at and in front of the root of the tail, behind the shoulder blades and sometimes (especially in Iberian horses) strands of fat next to the long back muscle that look like extra lateral lobes. We also sometimes see a thickening around the navel that manifests itself in a lobe in front of the udder in the mare and in the geldings (also in stallions but they have less tendency to fat than geldings due to their higher testosterone level) a swollen tube with sometimes also a fat lobe for the tube.

The horse’s movement pattern also begins to change. Animals become stiff and stiff, walk short and sometimes a bit like on eggs and tire quickly. The stiffness is especially noticeable when checking the gates at the vet, it then seems as if the animal is trapped in its own body. The musculature often feels hard on palpation and is certainly not flexible and malleable! What you are actually seeing are the accumulations of the fat derived from glucose, which is stored in places in the body where it is least harmful. Often a lot of fat has already accumulated in the liver, but that cannot continue indefinitely. There is still room for storage in the subcutaneous fat and connective tissue, especially at the above locations. Fat is also accumulated in and around the muscles.

Increased insulin levels can sometimes already be measured in the blood, even with a normal sugar level. The best evidence for true insulin resistance is when insulin levels are elevated after the horse has fasted for 12 hours.


Laminitis is the most severe problem that occurs in the insulin resistant horse. Due to the large amounts of sugar in the intestine, the composition of the intestinal bacteria changes. Usually it is the Streptococcis Bovis that gets the upper hand in the intestine, which causes changes to the intestinal wall and the release of toxins (poisons). These toxins cause a process of detachment of the intestinal wall at the level of the basement membrane. This is a layer of cells beneath the lining of most hollow organs. This detachment process releases enzymes that cause a separation of the basement membrane and the layer above it. This is useful in the intestine, because the absorption process of the toxins can be stopped. However, these enzymes also enter the blood. In this way, these substances reach the entire body where they can cause the same reaction wherever a basement membrane is present. Also in the hooves. Underneath the horny layer of the hoof is also a basement membrane and so the hoof is released from “life” there.
This process has been extensively researched by Doctor CC Pollit. These two processes have also been demonstrated by Pollit in parallel in laminitic animals. When there is a reduced blood flow in the feet due to the clogging of the vessel wall due to the deposition of fat, the foot does not have sufficient circulation, which can lead to laminitis. This is comparable to a reduced blood flow to the feet of people with diabetes. In a postpartum mare with metritis caused by a retained placenta the release process will mainly take place at the enzyme level, but in an overconditioned animal, the reduced blood circulation in particular will cause problems.

Inflammation (Low Graded Inflammation, LGI)

Fat tissue is a source of certain cytokines. These are proteins that are involved in blood pressure regulation, the development of inflammation, immunity, insulin sensitivity, glucose metabolism, appetite, energy balance and hemostasis. These substances are excreted by fat cells. They increase insulin sensitivity, but are excreted less when overweight. Macrophages in adipose tissue secrete pro-inflammatory cytonins.

When overweight, the percentage of macrophages increases, including the amount of pro-inflammatory cytokines. These cytokines enhance insulin resistance, because infections and inflammation in the body require a higher glucose level in the blood, which is an energy supplier for the immune system. The stop signals needed to successfully control inflammation (such as vitamin D or omega-3) are insufficiently present, leaving a horse in a low-grade inflammatory state. This low graded inflammation can lead to endothelial or epithelial dysfunction, plaque formation, micro- and macrovascular damage, as well as respiratory infections.

Skin complaints / Tail and mane eczema

As mentioned above, too much fat storage leads to increased macrophage activity with pro-inflammatory substances (LGI). Eczema is an increased macrophage activity in the skin. Tail and mane eczema is another LGI. The tail set and mane are precisely those locations in the horse with the greatest amount of fat. With LGI, the immune system is weakened, which means that the Culicoid mosquito has a greater chance of causing damage. This maintains an inflammatory response. Fat tissue is also a storage place for waste products and toxins. These cause itching (chafing). More damage occurs, so more inflammation and a vicious circle arises.

The treatment of insulin resistance

1. Adjusting the diet

Nonstructural carbohydrates such as corn, wheat or wheat bran, barley, oats and molasses (foods with a high glycemic index) should be limited. Sufficient roughage (with a low sugar content) should be given, such as straw, hay or ‘lean’ grass.

2. Reduce stress

Sufficient sunlight and outside air, living with conspecifics and sufficient exercise reduce the stress symptoms.

3. Supplementation of (essential) nutrients

When there is a magnesium deficiency, this can be supplemented. Supplementation with Omega-3 fatty acids and Vitamins A and D also reduces the risk of insulin resistance and inflammation.

4. Phytonics Gluco balance

Phytonics developed Gluco balance in the fight against insulin resistance. Gluco balance promotes a balanced blood sugar level. It causes the receptors to become more sensitive to insulin, which improves glucose absorption. It also regulates the liver, this organ plays an important role in the (glucose) metabolism. In diabetes mellitus, the immune system is disturbed, which often manifests itself in an increased susceptibility to infections and abnormal wound healing. Damage to blood vessels is also a complication of a disturbed glucose balance, because a too high glucose level greatly increases the number of reactive oxygen compounds in the blood. Gluco balance therefore contains anti-oxidants and immune stimulants.

Gluco balance can be used for hypoglycaemia and insulin resistance and all conditions that can arise as a result of insulin resistance, such as tail and mane eczema, laminitis, tying-up or respiratory problems.

Gluco balance is sold through your vet.

source: and Charlotte Willekens

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