Insulin Resistance mimics Cushing’s disease in many ways, although the horse does not have the benign pituitary adenoma present in the Cushing’s animal. Diagnosis is based on clinical signs (abnormal body fat distribution, abdominal fat, cresty neck, fatty shoulders, swollen sheaths in geldings), in combination with blood tests. Samples are usually taken for insulin, glucose and sometimes triglyceride levels.

Although affected animals may be overweight, it is not always so. Most tend to be “easy keepers”, resistant to losing weight, or they may have been overweight as youngsters. Founder is usually a feature at some point, with changes seen in the hooves such as founder rings, or expansion of the white line, suggesting some founder has occurred despite the absence of apparent foot pain.

The Pathology of IR What exactly is IR and why do certain types of horses appear more susceptible to the condition? Normally, when carbohydrates are digested, they are converted into glucose which is absorbed through the gut wall and enters the bloodstream. Here, the hormone insulin acts like a key, allowing glucose to enter cells where it is used as an energy source by the body. Conversely, when glucose levels in the body drop, the production of insulin stops.

Body fat was once thought to be just an energy reserve and protector of vital organs. Certain types of body fat, however, especially in the abdomen, are now thought to be actively involved in a number of metabolic processes, including cortisol production. One consequence of increased body fat is that it can lead to an increase in the level of cortisol produced. Cortisol is a natural steroid hormone, that among its many functions inhibits the action of insulin and provokes the flight or fight response to stress.

With high body fat stores, cortisol production levels remain high and are not switched off, leading to increased circulating levels of cortisol. This further inhibits the action of insulin, encouraging some of the cells to become “insulin resistant”, preventing the normal uptake of glucose by these cells and leading to high circulating blood glucose levels. But the body still needs an energy source to function correctly, so the liver starts to break down stored fat reserves (gluconeogenesis).

So how do wild horses survive? This process of storing and then using up body fat is believed to explain how tough, native breeds (ponies, Morgans, Paso Finos, Peruvians, Arabians) evolved in order to survive harsh winters. During the late spring, summer and fall when weather is warmer, food more plentiful and higher in sugars, these horses build up their stores of body fat. This natural build-up of fat ultimately leads to an increase in circulating cortisol levels, “insulin resistant cells” develop and as a consequence even more fat is laid down, which means the animal enters winter with a generous layer of body fat.

During the winter and early spring, when the weather is cold, food is scarce and of low nutritional value, the horse can draw on these fat reserves to provide the energy needed to help keep himself warm. When the fat reserves are exhausted at the end of the winter, cortisol levels naturally drop, insulin resistance is reversed, and the animal arrives lean yet healthy in the spring, ready to start the whole cycle again.

IR has arisen perhaps partly due to genetics and breeding, but also to the way in which horses and ponies are managed today. High levels of blood glucose, whether obtained excessively from the diet or because of insulin resistant cells, will eventually be converted and stored as fat, as seenin wild ponies. Unlike their wild cousins, however, pampered domesticated horses are never required to go through the scarce food times of winter. We turn them out onto rich pastures, where they have no need to expend any energy searching for food. We then exacerbate the problem by giving them additional forage, providing inadequate exercise or activity, and then when the weather turns cold we cover them up with snug rugs, removing the need for them to expend energy to keep warm! No one wants to see a horse suffer, but we have to realise that we are effectively turning them out onto a “running buffet” 24/7, with little or no exercise to work off the energy generated.

How Can Herbs Help? First, it is important to emphasise that any herbal supplementation should be used in conjunction with a steady gradual fitness/ weight loss program. Regular exercise is essential to encourage loss of body weight, and a greater muscle mass will help with fat metabolism (muscles burn more calories). Daily turnout is vital; horses and ponies were designed to graze while on the move, which again encourages the burning of calories. Many of the herbs that can be utilised are exactly the same ones I would prescribe for an individual suffering from Type 2iabetes, a very similar condition to IR, which produces many of the symptoms we see in IR horses (obesity, lethargy, poor circulation, muscle wastage etc.).

In this instance I would select herbs that can help: • Reduce glucose and insulin levels in the blood. This is the same action as Metformin, one of the main drugs used in IR • Reduce absorption of glucose from the gut.
• Assist in the absorption of excess glucose in the bloodstream.
• Promote cellular uptake of glucose.
• Support liver function and regeneration – vital for efficient fat metabolism and removal of blood toxins.
• Support bile salt production.
• Support digestive process and gut health.
• Normalize insulin sensitivity.
• Reduce blood lipid levels.
• Improve blood circulation.

This article should give you an indication of how herbs can be used, in conjunction with dietary and exercise programs, to help support horses with IR.

Glossary of helpful herbs Artichoke leaf (Cynara scolymus) is hypoglycemic and hypolipidemic. Artichoke significantly reduces serum cholesterol and triglyceride levels. It is why we eat it at the beginning of meals as an appetizer; with its “bitter” action, it encourages the production of digestive juices and bile salts which are critical for digestion and absorption of fats and fat soluble vitamins. Artichoke is also a prebiotic that will help encourage production of “good” hind gut bacteria, and improve liver function necessary to help break down stored fat. Psyllium husks (Plantago major) contain mucilage (a plant polysaccharide), a class of soluble fiber which is very hydrophilic (water-loving) and when ingested traps water in its cage-like structure, forming a gel and swelling to many times its original volume. Mucilages are a class of soluble fiber and psyllium in particular has been well studied and shown effective at lowering blood cholesterol, insulin and glucose levels. Soluble fiber helps retain glucose in the gut and reduce blood insulin levels after eating. The plant has also been shown to offer an anti-inflammatory and healing action on the digestive tract, as well as acting as a prebiotic. These actions are particularly relevant, as it has been suggested horses may struggle to absorb nutrients from their food if the integrity of the gut is compromised. Lack of nutrient absorption has been linked to the onset of some forms of founder. Fenugree (Trigonella foenum – graecum) is hypoglycemic and hypolipidemic and excellent for overall digestive health. It contains galactomannan, which aids with fat digestion. As an internal demulcent, it reduces inflammation and soothes and heals the mucosa of the stomach and intestines. Poor gut function has been linked to poor nutrient absorption and the increased risk of founder. Milk thistle (Silybum marianum) is a cholagogue, stimulating the production and flow of bile and aiding digestion of fats. Milk thistle is also hepatoprotective and has a strong antioxidant action (offering ten times the antioxidant action of vitamin E). Constituents in the seed also help reduce the permeability of the liver membrane, helping to protect the organ from damage by excessive circulating corticosteroids. The plant has been shown to enhance the synthesis of RNA and proteins and consequently cellular regeneration, speeding up the renewal of damaged liver cells. Garlic (Allium sativum) is hypoglycemic and hypolipidemic, effectively reducing the levels of glucose in the bloodstream as well as lowering blood lipid levels and total cholesterol. Garlic has been shown to help clear fats accumulating in arteries, and is used extensively for diabetes. Garlic also acts as a prebiotic and as a chologogue. Ginger (Zingiber officinale) contains gingerol, which has been shown to have prolonged hypoglycemic activity. Ginger is also a vasodilator and strong circulatory stimulant that will help encourage healthy blood supply to the vital organs and limbs. Goats rue (Galega officinalis) is hypoglycemic, and like psyllium, inhibits the absorption of glucose from the gut, thereby reducing the levels of sugar in the bloodstream. It also potentiates the effects of insulin, promoting uptake of glucose by the cells. Kelp (Fucus vesiculosis) has anti-obesity properties, and is rich in organic minerals, biotin and methionine needed to ensure healthy hoof growth, magnesium (low levels have been linked to IR), plus other minerals, trace elements, amino acids and vitamins. Mint (Mentha piperata) is a digestive carminative, soothing to the GI system. It is also a good source of potassium and magnesium. Nettle (Urtica dioica) is a circulatory stimulant, rich in vitamin C, iron, sodium and dietary fiber. Cleansing and anti-diabetic, it will stimulate blood supply to vital organs and in particular to the limbs and feet.


Hilary Self is a Medical Herbalist, a member of the National Institute of Medical Herbalists, and a member of the NASC Scientific Advisory Committee. She is also co-founder of Hilton Herbs Ltd., which has been manufacturing and formulating herbal supplements for animals for 22 years. In 2004, Hilary received the Nigel Wynn award from the National Institute for innovative projects in herbal medicine, in recognition of her clinical trials into the application of herbs for horses with Cushing’s disease. Hilary is the author of two books: A Modern Horse Herbal and A Veteran Horse Herbal.