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Just a few years ago, veterinary literature stated: “Diabetes is unknown in horses!” – until the emergence of the first cases of equine diabetes. However, it’s crucial to distinguish between type 1 and type 2 diabetes.

Type 1 diabetes, formerly known as “juvenile diabetes,” is characterized by the destruction of the insulin-producing islets of Langerhans in the pancreas. When these islets are destroyed, insufficient or no insulin is produced,

leading to inadequate regulation of blood sugar levels. While type 1 diabetes is prevalent in dogs and cats, it is not typically found in horses..

In the last decade, however, there has been an increase in cases of type 2 diabetes in horses, also known as insulin resistance. This clinical condition was initially a subject of controversy until it was ultimately acknowledged as a reality: yes, horses can indeed develop diabetes, with type 2, or insulin resistance, being the known form thus far.

What does insulin resistance mean?

When a healthy horse consumes its feed, the blood sugar level increases following the digestion of sugar, starch, cellulose, or pectin. The key distinction among these nutrients lies in the rate at which the blood sugar level rises: sugar and starch are broken down rapidly and sharply in the small intestine, resulting in a quick and steep increase in blood sugar levels.

On the other hand, the digestion of cellulose and pectins occurs more gradually in the large intestine with the assistance of microorganisms. As a result, sugar molecules from these sources enter the bloodstream at a slower pace. When the blood sugar level rises, the pancreas secretes insulin.

Insulin then binds to specific receptors in the liver and muscle cells. Subsequently, liver cells absorb sugar, converting it into the storage form glycogen. Once the glycogen stores are saturated, any excess sugar may be converted into fat, which is then stored in adipose tissue.

Horse eats in the pasture
If the horse eats sugar, the blood sugar level rises quickly. © Adobe Stock / Eileen

The muscle cells also play a role in absorbing sugar from the blood, converting it into glycogen. However, unlike the liver, this absorption ceases once the glycogen stores reach capacity. During physical exertion, such as exercise, sugar and glycogen are utilized as sources of energy, leading to a depletion of sugar and glycogen levels within the muscle.

As a result, the muscle cells continue to draw sugar from the bloodstream until the blood sugar level drops below a critical threshold.

At this point, the pancreas releases glucagon, which binds to receptors in the liver. The liver responds by converting glycogen back into sugar and releasing it into the bloodstream, thereby maintaining a constant blood sugar level within narrow limits.

In horses fed a species-appropriate diet, the metabolic system is primarily adapted for slowly digestible structural carbohydrates such as cellulose or hemicellulose, which enter the bloodstream with a delay. Sugar and starch play a secondary role in the natural equine diet.

Blood sugar fluctuations in horses

However, this paradigm shifts drastically with human feeding practices. Often, large quantities of concentrated feed are provided to horses, following the mindset of “I eat three meals a day, so my horse needs a full trough three times a day.”

Most compound feeds also contain thermally processed grains, wherein complex starch molecules have been broken down through heat treatment. This accelerates the absorption of sugars from starch into the bloodstream.

However, the equine organism is not naturally equipped to handle such rapid and frequent fluctuations in blood sugar levels. After consuming a sugary feed (i.e., concentrated feed), the horse typically requires around six hours on average to return to its baseline blood sugar level. Yet, by this time, the next meal is often already waiting in the trough.

Consequently, blood sugar and insulin levels fail to return to normal levels. Over time, this constant exposure to insulin leads to reduced sensitivity of receptors in the muscle and liver cells – a condition known as insulin resistance.

What does selenium have to do with this?

However, there are cases of horses that have never been fed muesli in their lives yet still exhibit insulin resistance. Upon reviewing the medical history of these horses, a selenium deficiency is often diagnosed in the blood tests. Consequently, these horses are administered concentrated selenium preparations to address the apparent deficiency.

However, it is now recognized among experts that many laboratories employ upper limit values that are excessively high. Studies indicate that lower limit values between 28 and 40µg/l are entirely normal, contrasting with the 100µg/l threshold commonly utilized by most laboratories.

Moreover, it is understood that the selenium plasma level, determined in blood tests, does not accurately reflect the horse’s selenium status. For most blood values, tissues act as buffers to maintain stable blood levels. For instance, if blood calcium levels decline, calcium is drawn from the bone to restore equilibrium.

However, selenium behaves differently; if tissues require selenium, it is initially extracted from the blood. Upon selenium supplementation, tissues are replenished first, potentially leading to excessive accumulation (sometimes reaching toxic levels), before alterations in the plasma level occur.

Thus, it is perilous to administer selenium supplements solely based on a selenium deficiency in plasma—further complicated by erroneous limit values. Excessive selenium accumulation in tissues interferes with insulin signaling within cells, disrupting the connection between receptors and the entry gate for sugar molecules into cells. This disruption contributes to symptoms of insulin resistance.

Type 2 diabetes resulting from selenium supplementation exceeding the physiological level of natural nutrition has been extensively studied and documented in humans. Consequently, clear warnings against selenium supplementation have emerged. Unfortunately, this caution has not yet permeated the veterinary sector.

Becoming more sensitive to insulin again

To restore insulin sensitivity and normalize metabolism, horses affected by insulin resistance require treatment.

Various micronutrients have shown effectiveness in this regard. For instance, bioavailable chromium sourced from specially cultivated chromium yeast, along with grapefruit seed extract and certain organic magnesium and potassium compounds, have proven beneficial.

Furthermore, naturopathy utilizes several plant-based active ingredients known to improve type 2 diabetes. One such example is mate, a popular remedy in South America. These natural remedies can aid in improving insulin sensitivity and supporting overall metabolic health in insulin-resistant horses.

OKAPI PankrEMS forte helps horses to regain their balance. © OKAPI GmbH

For this purpose, we recommend OKAPI PankrEMS forte, a supplement tailored for horses with insulin resistance. This formulation targets the specific nutrients necessary to assist affected horses in restoring their metabolic balance.