The clinical signs, laboratory findings, and treatment of this condition more closely follow those of Metabolic syndrome in humans. Metabolic syndrome is a relatively new condition being recognized in human medicine where the cells become resistant to insulin and the glucose from the food cannot get into the cells.
The symptoms seen in horses with Metabolic syndrome range from mild to severe and can begin as early as seven years of age. Horses in their late teens and those more than twenty years old can exhibit many of the "classic" signs of what has been called Cushing's disease, including obesity, long hair, increased urination and drinking, muscle wasting and difficult-to-treat laminitis. However, many of the younger horses show poor or slow shedding, obesity with lumpy fat pads, poor immune systems, chronic infections and, in some cases, laminitis.
There are many potential reasons for altered glucose metabolism and Metabolic syndrome. Some of the contributing factors are chronic stress, high sugar or rich feed intake, overuse of drugs and vaccines, the feeding of soy products, pyrethroid fly sprays, genetics, overly rich feed, and possibly the frequent use of glucosamine.
Treatment consists of supplying the nutrients for healthy glucose metabolism, often in combination with homeopathy or Chinese herbs, as well as making some lifestyle changes.
Many horses are living the same high-stress lives as their owners do. Competition horses are often on the road two to five days a week, with little turnout time and constant work. Many pleasure horses also have little turnout time or companionship. Because horses are naturally herd animals who thrive on running free and playing with their buddies, this life is very unnatural.
High sugar/molasses feeds are commonly used in horses. Fertilized fields or any rich grass is unnatural for an animal who evolved to eat sparse scrub, with little food in the winter. In humans, increased insulin levels can begin in childhood. Most of the prepared diets for foals and young growing horses are extremely high in sugar.
Drug and vaccine use
The overuse of drugs and vaccines is rampant in many horses, especially horses used in competitions. Many competition horses receive multiple drugs during a show. Influenza and herpes vaccines are often given every two months, with a large group of vaccines given twice a year as well. The level of internal stress created by the use of such a large quantity of drugs has a negative effect on the entire body.
Soybean meal has been a large part of horse feed for many years. Some research shows a negative effect of soy on glucose metabolism. Soy can adversely affect the thyroid gland. Reduced thyroid function has a negative effect on insulin resistance. Creep feed and young horse rations are very high in protein, and that protein is derived primarily from soy.
Pyrethroid-based fly sprays
Pyrethroid-based fly sprays (and flea sprays) can also depress thyroid function. They are generally considered safe by the EPA. The latest products are made from 45 to 55 percent pyrethrins and are designed to stay on the skin for two weeks. There is no research to show that these levels are safe, since the average fly spray that has been studied is around 1% pyrethrins. Overhead spray systems put out doses of the spray every few hours or more often. This spray goes onto the horse, into the water or feed bucket and onto the hay as well as into the respiratory system of the horse.
Glucosamine is being fed to horses in large quantities, mostly for arthritis-related conditions. The effect of short-term glucosamine given intravenously in humans and laboratory animals is to increase insulin resistance. There is no proof that this compound causes problems, however, there are some indications that it may be best to avoid it in horses with Metabolic syndrome who are not responding well to other treatment.
Genetics (thrifty phenotype)
Genetics plays a role in insulin resistance and sensitivity to rich foods. In humans the "thrifty genotype" has been described. The body of both humans and horses is well adapted to periods of famine and is capable of storing fat easily when plenty of glucose (food) is available. Concentrated feeds and rich hay are added to already rich grass and the easy keepers become obese rapidly.
Treatment is multifaceted and is the best example of a truly holistic approach, as each horse is different, and each needs to be reevaluated regularly to see what is needed. However, there are some basic ingredients that all horses can benefit from.
Feed: High quality nutrients should be provided and probiotics used for at least a few months to correct any imbalance in intestinal flora. A high fiber, low carbohydrate diet can be used as well as some of the higher fat and fiber diets, though many horses will become too fat on the high calorie diets. Grass or other lower protein hays can be given free choice. The feed should be low in sugar and all sweet feeds should be avoided. Treats should be minimal and limited to apples. A simple grain mix of corn, oats or barley can be used. One possible combination is coarse cracked corn (about 25%), barley (about 35%) and oats (about 45%). Barley may be one of the best foods to use with horses who have laminitis.
Minerals: One of the most important aspects of any nutritional program for horses is the use of free-choice minerals with the salt fed separately. Many Metabolic syndrome horses will eat large quantities of minerals for extended periods of time, indicating their need for minerals. Magnesium affects insulin secretion and its action in the cells. Chromium helps make muscle more sensitive to insulin so glucose can be taken into the muscle cells more easily. Vanadium or vanadyl sulfate has actual insulin-like effects on glucose metabolism.
Essential fatty acids: Essential fatty acids (EFAs) are needed to help make the cell wall more sensitive to insulin. High doses of flax and hemp oil (6-8 tbsp. per day) or naturally stabilized hemp or flax meal (6-8 oz per day) provide EFAs in a therapeutic dose and palatable form.