From Sugars to Glucose

When a horse consumes sugar-rich foods such as grains and grass, its body breaks down these carbohydrates into glucose. This leads to an increase in blood sugar levels. In response, the body produces insulin, the hormone that helps transport glucose into the body’s cells. Glucose serves as an energy source for all the daily functions of the cells.

Insulin Resistance

With IR (Insulin Resistance), the body becomes less sensitive to insulin. When large amounts of sugar are constantly consumed and blood sugar levels remain high, problems begin to develop. This is common in overweight horses and/or when the diet contains too many (free) sugars. Such consistently high blood sugar causes the cells to become less responsive to insulin. The insulin receptors on the cell membranes start reacting poorly to the hormone. Additionally, a deficiency in certain minerals, such as magnesium, can further reduce insulin sensitivity. When a horse doesn’t respond well to insulin, glucose is absorbed less efficiently and the blood sugar levels remain elevated.

Confused Cells

The cellular mechanisms behind IR in horses are currently the subject of scientific research—particularly because IR plays a significant role in the painful and serious condition known as laminitis. The precise processes of nutrient absorption and post-meal insulin dynamics greatly influence the development of IR. In horses, some of these processes seem to function differently than in humans and other mammals. What we do know is that rapidly digestible carbohydrates (free sugars) in the diet, and even certain amino acids, are important contributors to the development of IR. A long-term excess of food—especially sugar-rich food—is one of the primary causes of IR, particularly if the horse is already overweight. At the same time, IR itself greatly affects how nutrients are absorbed into the cells and impacts hormonal processes. For example, insulin resistance significantly affects protein processing and muscle metabolism. In other words, IR has complex effects on the body.

Consequences of Insulin Resistance

In horses with IR, sugar metabolism and glucose uptake by the cells are less efficient. A horse with insulin resistance cannot properly process the sugars from food (such as grass and concentrates). This can lead to fat storage, infections, and loss of energy. The pancreas also becomes overworked. Eventually, problems such as laminitis, Cushing’s disease (PPID), and sweet itch may develop. Overweight and sugar-rich diets are major causes of IR, but long-term stress, gut infections, and hormonal imbalances can also trigger IR. Cold-blooded breeds and ponies are generally more sensitive to IR than other horse breeds.

Symptoms of IR

Horses with IR can often be recognized by the following signs:

• Hardened and thickened crest
• Fat pads above the tail base
• Itching and rubbing of the tail and mane
• Short and stiff movement
• Tense or hard muscles
• Swelling near the navel (in mares) or sheath (in geldings)
• Frequent overweight (but not always)

Nutrition, Exercise, and Supplements

You can support a horse with IR through proper nutrition, appropriate exercise, and supplements such as magnesium and cannabinoids. More detailed information on this topic is available in other articles on this website.