Insulin resistance in horses

Learn more about insulin resistance in horses including causes, symptoms and potential treatment options.


Equine insulin resistance, also known as Equine Metabolic Syndrome (EMS), is becoming a more publicly known condition, however, it is a complicated disease that is still not completely understood. Read on to find answers to questions surrounding equine insulin resistance.

What is insulin resistance?

Insulin resistance is a condition in which body tissues have a decreased responsiveness to insulin. Insulin is an extremely important hormone for the body; it regulates glucose (sugar) metabolism by instructing tissues to take in glucose from the blood stream after eating a meal, and it stimulates tissues to use that glucose to synthesize (make) glycogen, which is a way of storing energy.

In healthy tissues, insulin will bind to receptors on the tissue, which will send a signal that stimulates the cells to take in glucose. However, in insulin-resistant tissues, there is a problem that occurs with the signal after the insulin molecule binds to the receptor. This problem means the signal is not properly sent through the tissue, and glucose is not taken in from the blood stream. This causes the blood glucose level to remain high, which is a signal for the body to produce more insulin to try to get the tissues to take the glucose in. This can lead to clinical hyperinsulinemia (chronically high insulin concentration), which can cause more health issues.

What causes insulin resistance?

The exact causes of insulin resistance are unknown, but there are some factors that may influence its development. Obesity is the biggest risk factor for insulin resistance. Age is another one; older horses (older than 20 years) have an increased risk of developing Equine Metabolic Syndrome. Increased age is often also associated with Cushing’s disease, a frequently diagnosed endocrine abnormality in horses. 

Breed can also play a role. It has been shown that ponies, Arabians and Morgans are more likely to develop insulin resistance than Standardbreds. Lastly, it has been thought that diets high in simple starches or with a high glycemic index could increase the chance of developing insulin resistance, but this claim has not been proven.

What are the symptoms of insulin resistance?

There is not a specific set of symptoms that an insulin-resistant horse will show, but there are signs that might indicate insulin resistance. These include abnormal fat deposits, usually on the crest, rump and above the eye, excessive urinating and drinking, and potentially developing laminitis. However, if a horse displays these symptoms, it is not always because of insulin resistance. Talk to your veterinarian to determine the exact cause and discuss different risk factors.

How can you treat insulin resistance?

The best way to treat insulin resistance is to prevent it in the first place. This can be done by feeding a proper diet, ensuring your horse gets plenty of exercise and maintaining a healthy body condition score of 5-6. However, if your horse is already insulin-resistant, changing its diet and exercise is the best way to maintain a good quality of life. Feeding low glycemic index feeds, like plain beet pulp and warm-season grasses, will also help to lower blood glucose and insulin.

Increasing the amount of exercise your horse gets is also very important in maintaining a healthy horse. Start with exercising two to three times a week for 20-30 minutes and gradually work up to five to seven times a week.

By adopting these management changes, you should be able to give your horse a good quality of life and keep them happy and healthy for more years to come.

Want to learn more? Read “Insulin resistance in horses: A review” by Kaczmarek, K. and others.

The Michigan State University Extension science team’s goal is to increase science literacy across Michigan. One way we support an increased interest in science is to provide information and ideas for engaging youth in exploring their world. Adults can help youth increase their science literacy by encouraging them to ask questions and discover answers. Exploring our beaches is just one way to engage youth in STEM (Science, Technology, Engineering and Mathematics).

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