When a horse has Insulin resistance it means that the body produces enough insulin, but the cells in the body no longer respond well to the insulin. They have become insensitive to it.
To understand what insulin resistance is, we first have to look at how the horse's carbohydrate metabolism normally functions.
Carbohydrates
Carbohydrates are broken down into glucose by the digestive system, 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.
Insulin
The amount of glucose in the blood is regulated by insulin. This is a hormone secreted by the pancreas. Insulin ensures that glucose is absorbed by the cells.
The more glucose is released into the blood from the digestive system, the more the cells need to absorb to keep the glucose level down. So more glucose means more insulin. What the brain and muscles don't use is stored in the liver or converted to fat.
Conversely, the glucose level decreases, because the supply stops, or because the muscles consume a lot of glucose, so the conversion of glucose into fat must be stopped. The production of insulin is then reduced.
Two stages of insulin resistance
Pre-diabetes stage, at this stage insulin resistance is compensated by the pancreas by producing more and more insulin. The insensitive cells then still absorb enough glucose due to the increased amount of insulin. The glucose level is still acceptable, but the insulin level is significantly increased.
This is the most common stage found in horses.
The problem with this stage of insulin resistance is that the health complaints are vague and the cause is often not recognized. The symptoms are treated as well as possible, but as long as the cause is not recognized, its like `Shutting the stable door after the horse has bolted`.
If, despite the high production of insulin, the glucose level still isn’t under control, then the next stage of insulin resistance is reached. The pancreas becomes 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 to death. At this stage, the body will lose weight. Many horses never reach this stage, but when this happens, the animal will lose weight and suffer more and more ailments that can eventually lead to death.
Insulin resistance symptoms
Insulin resistance symptoms are diverse and partly dependent on the individual.
The symptoms can occur separately or together.
Laminitis
Horses that have had laminitis are less able to process glucose and suffer from insulin levels that are four times higher than normal, which indicates insulin resistance. Susceptibility to laminitis is therefore the most common symptom. The horse will be able to get laminitis at the slightest or least. Despite the fact that insulin resistance and laminitis have a clear connection, it is not yet clear exactly why this connection exists.
Weight problems
Most horses with insulin resistance are overweight. The consistently high insulin content makes it impossible to break down fat, keeping these horses overweight even if they are on a strict diet. It is striking that the fat mainly concentrates at the mane crest, tail set and flanks. The 'hard neck' is typical of horses suffering from insulin resistance. Often this is also a vicious circle: too high insulin levels ensures fat retention, but the fatter the animal, the more insulin it needs. Underweight arises in a minority of cases.
Listlessness
Horses suffering from insulin resistance have less energy. They struggle to 'work' during training. Due to the consistently high insulin level, glucose cannot be released quickly enough when the muscles request it.
Skin issues
Owners with horses that suffer from insulin resistance also often report that the horse suffers from skin problems, injuries heal more slowly, and (fungal) infections occur more often.
Some causes of increase in the number of insulin resistance cases
Nutrition
Horses have adapted perfectly to their natural diet in millions of years of evolution. However, we humans feed the horses something different from what they are supposed to eat naturally, and provide it in a different way. At The Horse Therapist we solve this by feeding horses naturally with herb mixes in addition to a base of good roughage.
Fast carbohydrates from cow grass and concentrates
Horses are collectors by nature and eat practically nothing but stalky, free arid grass consisting mainly of longer carbohydrate chains, such as cellulose and starch, as well as herbs, plants, tree bark and tubers. We humans, however, feed horses concentrates and specially grown grass, which often contains concentrations of short carbohydrate chains. Now all carbohydrates must be converted into glucose by the digestive system, but the time it takes to do this varies by carbohydrate. Short carbohydrate chains are converted much faster than the longer carbohydrate chains that horses naturally eat. Instead of a steady stream of carbohydrates slowly released by the digestive system, the horse is faced with a sudden burst of carbohydrates that quit quite abruptly. Now insulin is a hormone, and hormones are well suited to control slow-moving processes. They have more difficulty with rapidly changing processes. When the carbohydrates are released from the digestive system fairly quickly, a lot of insulin has to be produced in a short time. When the supply of carbohydrates suddenly stops (because the quickly digestible sugar has run out), the insulin is still in the blood, and the cells continue to take up glucose well while the glucose level is already low enough. The glucose level then varies between high and low much faster, and the extremes are much more extreme than nature had foreseen.
Molasses
Molasses is a widely used ingredient in concentrates (such as muesli) because it counteracts dust and horses like it. Molasses is a residual product from the sugar industry and mainly consists of quickly digestible sugars.
Grass
The grass that we feed our horses is specially selected for a high yield and as production grass for cows. In addition, it has been selected for a high yield as early as possible in the year, which means that the grass must be frost-resistant (at night). These types of grasses are therefore perfectly capable of producing a natural antifreeze: fructan.
Fructan is a particularly quickly digestible carbohydrate, when a lot of fructan is produced by the grass (low temperatures, combined with a lot of sunshine, as often occurs in the spring), the horses get much more fast carbohydrates.
Portions
Horses naturally eat almost continuously. The digestive system therefore delivers a continuous flow of carbohydrates. However, we humans feed the horses in portions. The fluctuations in the glucose supply are now much greater than was naturally intended, and that problem is exacerbated when we give the horses fast digestible food.
Magnesium deficiency
A magnesium deficiency seems to be increasing in horses. Magnesium deficiency makes the cells less sensitive to insulin. In horses, the administration of magnesium often appears to reduce insulin resistance. For this reason, a magnesium cure is also increasingly used in the treatment of laminitis horses.
Being overweight
The most domesticated horses and ponies are overweight. Insulin resistance and obesity often go together. The less mass, the less insulin is ultimately needed.
Too little movement
Exercise is of course healthy, but it also ensures higher glucose consumption. Horses travel 30 to 50 kilometres daily in the wild. In our way of keeping horses, they practically never get there. The less exercise, the greater the chance of malfunctions in the carbohydrate metabolism.
Old age
As horses age, the risk of insulin resistance increases.
Treatment options
Nutrition
Provide a steady, calm flow of carbohydrates, trying to keep the horse from eating per serving. If the horse does not receive concentrates, a horse can be offered unlimited roughage, so that the horse can eat in small amounts throughout the day.
If he cannot get unlimited roughage, try feeding him small portions as often as possible.
Feeding herbs in addition to the roughage supplements the horse's needs and helps with or prevents problems.
Magnesium
Insulin resistance can result from a magnesium deficiency. To start up properly, it may be important to add magnesium. Magnesium increases sensitivity to insulin.
Being overweight
Reducing obesity is one of the important steps. The lower the weight, the better the cells respond to insulin. The problem may be that horses with insulin resistance are often difficult to poke for physical activity. In addition, they appear to lose weight with difficulty, even with a very strict diet.
Movement
Movement ensures consumption of glucose. The more glucose is consumed, the less glucose has to be converted into fat, so the less insulin is required. By 'moving' we do not mean "riding for an hour in the arena", but rather the possibility to move continuously.
Hooves
Because horses with insulin resistance have an increased risk of laminitis, it is important to pay extra attention to the hooves. Frequent and regular movement, preferably over paved surfaces, ensures good blood circulation in the hoof, so that the risk of laminitis is reduced.
* written by Jente Driessen from HorseComplete and translated by Sharon Bronsveld from The Horse Therapist