If you’ve been involved with horses for any significant amount of time, you have surely heard terms like insulin resistant, metabolic syndrome and others, and maybe you are not always sure what they mean. The reason for this is that horse owners and even some veterinarians can use some of the terms interchangeably or indiscriminately, causing confusion. In fairness, it’s easy to do so because many metabolic conditions in horses have a similar set of symptoms, and some are treated in similar ways, but that does not mean they are the same disease. Let me try to offer some clarity by defining some of the most common metabolic conditions in horses.
Insulin Resistant or IR – An insulin resistant horse, often called an IR horse, is a horse whose cells are resistant to the normal hormonal signals given by insulin telling the cells to absorb glucose. This forces the liver to convert the excess glucose to fat. Horse that are insulin resistant don’t have a disease, per se, but rather a metabolic problem in the processing of simple sugars. Since insulin resistance is not a disease, there is no cure but only management, which consists of exercise and a low-carb, low-fat diet that is supported by well-balanced minerals. Horses that have other metabolic syndromes or diseases can also be insulin resistant, but in these cases the resistance is a symptom of the underlying disease or syndrome.
Before moving on to the next condition, it is helpful to understand that a syndrome is different than a disease. A syndrome is a recognized set of symptoms without a distinctly identifiable cause. A disease, on the other hand, may have a set of symptoms, but it also has an identifiable underlying cause that is known and can be identified
Equine Metabolic Syndrome or EMS – A horse with EMS is also generally insulin resistant, but the insulin resistance is one of several symptoms within the syndrome. Others include a propensity for fatty deposits in the abdomen, the crest of the neck, the eyes, and other areas; and chronic laminitis. It is thought that EMS originates when certain tissues produce abnormal levels of certain hormones. Like insulin resistance, there is no cure for EMS. It is treated in a manner very similar to simple insulin resistance; that is a low-carb, low-fat diet that is high in fiber, and supplements with proper levels of minerals and vitamins. A horse with metabolic syndrome is sometimes called a metabolic horse or Cushingoid horse. The term metabolic disease is also sometimes used to describe a horse with EMS, but its use is technically incorrect.
So now that you understand IR and EMS, it is easy to see how these terms very frequently get used interchangeably or indiscriminately. But it doesn’t stop there. Indeed, it starts to get even more tricky.
Cushing’s Syndrome – Cushing’s syndrome is a term often used interchangeably with equine metabolic syndrome. The reason for this is very simple: most experts agree they are one and the same, meaning they are the same set of symptoms, but still with an unknown cause. Equine Metabolic Syndrome has become the preferred term. Of course the symptoms are the same; insulin resistance, a propensity for fatty deposits in the abdomen, the crest of neck, the eyes, and other areas; and chronic laminitis. The treatment and management are also the same. Cushing’s syndrome or EMS is most often first recognized in younger horses. A horse that has Cushing’s syndrome (or EMS) is sometimes called a Cushingoid horse. This can be very confusing, because a horse with Cushing’s disease if also often called a Cushingoid horse, but the syndrome and the disease are different.
Cushing’s Disease - Cushing’s disease is caused by a tumor that grows in the pituitary gland, causing severe hormonal imbalances. There is no known cure for Cushing’s disease. Cushing’s disease can have the following symptoms: weight loss, excessive thirst and/or urination, chronic laminitis, a curly, non-shedding coat, poor muscle condition, a propensity to infections, and irregular fat deposits. Cushing’s disease is most often diagnosed in older horses. Cushing’s disease is treated differently than Cushing’s syndrome or EMS. It can include both diet and specific medication to treat the hormonal functions of the pituitary gland. For this reason, it is critical for a skilled veterinarian to diagnose a horse with metabolic symptoms to determine if they are part of the syndrome or the disease.
So, in short, here is how I remember what these different terms mean:
Hopefully this will help you understand the most commonly encountered metabolic problems in horses more clearly, whether you are discussing them with someone, or if you happen to have a horse that suffers from one of them. For the sake of clarity, whenever I discuss any of these issues and people start throwing around words like IR, metabolic and Cushing’s, I always ask for clarification so I know exactly what we are talking about. Not surprisingly, I find that people are not always sure.
As always, this article is not an attempt to diagnose or prescribe treatment for any particular equine health problem. If you suspect your horse is suffering from a metabolic disorder or any other health problem, it is critical to consult your veterinary professional for complete testing, diagnosis and treatment.
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