An Ancient Medicine Prospective of IR and Cushing’s Issues of the Horse

Chinese Medicine or TCM approach to the treatment of METABOLIC SYNDROME AND INSULIN RESISTANCE

Joyce C. Harman DVM, MRCVS

Cushing’s syndrome in horses is currently being frequently diagnosed. However, in studying the disease in more detail, the correct name that has been adopted is Equine Metabolic Syndrome (EMS). 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 or younger. Horses in their late teens and over 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. From a Traditional Chinese Medicine (TCM) perspective, it is possible to understand how the various patterns of the disease appear and why the winter laminitis cases are so hard to treat.

Many potential reasons exist 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, 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.

PHYSIOLOGY AND PATHOPHYSIOLOGY

GLUCOSE METABOLISM

Glucose, being water soluble, needs help being transported across the lipid membrane of the cell. The primary way for glucose to be transported into muscle and adipose cells is facilitated diffusion using the transmembrane protein GLUT 4. GLUTs 1, 2, 3 and 5 are transmembrane proteins used in other aspects of glucose transport. GLUT 4 remains inside the cell until it is activated by a stimulus such as insulin, exercise or a compound such as vanadium, all of which move the GLUT 4 into the cell membrane to transport glucose (1). One of the main reasons for insulin resistance is defects in the intra-cellular action of GLUT 4 preventing a normal response to insulin.

INSULIN RESISTANCE

Many EMS horses have elevated insulin levels in their blood (2) without concurrently raised or lowered glucose levels (3, 4, 5). Metabolic Syndrome is a group of symptoms related to insulin resistance or hyperinsulinemia (6). The cells show an inability to transport glucose into them. Insulin resistance occurs in as much as 25% of the non-diabetic population (7). So-called Cushing’s syndrome in horses has some of the same characteristics as Metabolic Syndrome (2, 7) has in people. Some of the specific symptoms are obviously different. However, the general seriousness of the metabolic derangements are very similar, including glucose metabolism and circulatory problems.

People who are susceptible to Metabolic Syndrome are frequently from a genetic type considered “thrifty,” or in horse terms “easy keepers” (8, 9). In this type of individual, horse or human, the body is very efficient at storing fat for times of need, and in fact, if fed less, they often become more efficient at storing fat. In humans much of the fat stored from impaired glucose metabolism is distributed centrally, especially around the abdomen. Many horses store their fat in specific places; fat pads on their body, fat above the eyes and cresty necks. The fat on their body frequently becomes lumpy instead of smooth and often this is the first sign that the horse’s metabolism is changing. In fact, if this author sees a horse that has changed from smooth fat to lumpy fat, no matter what the age of the horse is, that horse will be a candidate for treatment as all conditions are easier to treat at the earliest sign of the disease.

The cardiac involvement that occurs in humans may not be directly related to the syndrome in horses, however no research has been done in this area. Insulin affects the growth of smooth muscle cells in the arteries as well as lipogenesis in arterial vessels. Whether that has direct bearing on the laminitic horse remains to be seen. Dihydroepiandrosterone (DHEA) levels are not monitored in horses, however, in humans increases in insulin levels in some studies are shown to cause a decrease in DHEA. The decrease in DHEA is considered a cardiac disease risk factor.
In horses, it is not uncommon to see elevated insulin levels with normal blood glucose levels. In ambulatory equine practice, where it is often several hours or more until the blood samples are processed, it may also be necessary to collect a special glucose tube to get an accurate measure of blood glucose. The insulin is elevated because it is not able to get into the cells. Normally when a sugar or carbohydrate is eaten, the blood sugar levels increase, insulin is secreted by the pancreas, glucose is carried into the cells by the insulin and the blood sugar goes back to normal. In insulin resistance, the cell wall insulin receptors cannot transport glucose correctly (10, 11). About 25% of the hyperinsulinemic people become diabetic, however, in horses, the actual occurrence of diabetes is quite low, indicating a difference in physiologic response between the two species.

Hyperinsulinemia may contribute to hypertension through altering sodium and potassium metabolism. Hypertension does not occur in the equine, though it is unknown whether some of the electrolyte imbalances occur and what effect this may have.

The treatment of people with insulin resistance using natural medicine incorporates many of the ingredients used when successfully treating the EMS horses. The permeability of the cell walls to insulin is enhanced and nutrients are provided to help insulin and glucose pathways function better. The details are discussed below in the treatment section.

CHINESE APPROACH TO IDENTIFYING EQUINE METABOLIC SYNDROME

When we examine this condition from a Chinese perspective three distinct patterns are involved. This helps explain pieces of the puzzle that western medicine cannot. The Chinese explanations described here are a generalization, but will give the reader an introduction to the concept.

Horses affected with Spleen imbalances (Earth personalities) tend to be fat, easy keepers, have laid-back personalities and may or may not have some digestive disturbances (diarrhea, gas). They have a tendency to be more affected in the late summer and fall. The TCM pattern is generally Phlegm Damp, caused by the overeating of rich foods (grass, grains).

Horses with Liver imbalances (Wood personalities) may be fat or not quite as fat as the Spleen ones, may be better performance horses, have a more of a type A personality, may be mares, and have more problems in the spring time. The TCM pattern is Liver Yin deficiency, and can be caused by Liver Qi stagnation from stress, emotional imbalances. As the Liver Qi stagnates is causes heat, which damages the Yin.

Horses with Kidney imbalances (Water personalities) can be fat or thin, tend to be older (the Kidney fades in all animals and people with age), may show more classic signs of drinking and peeing, have a long coat and have more immune system issues. These are the wintertime problem horses, and here is the reason for laminitis that occurs in the winter. This is the season the Kidney is most active, but if it is weak then symptoms of its weakness occur. Kidney Yin and Yang deficiency laminitis cases are often the hardest to treat conventionally because they need a lot of metabolic support for the Kidney and the drugs just do not supply that. The TCM pattern is often Kidney Yang deficiency, which is preceded by Kidney Yin that has been deficient for a long time.

CONTRIBUTING FACTORS

STRESS
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 turn-out time and constant work. Many pleasure horses also have little turnout time or companionship. Since horses are naturally herd animals that thrive on running free and playing with their buddies, that life is very unnatural.

SUGAR INTAKE

High sugar/molasses feeds are commonly used in horses. Fertilized fields or any rich grass is unnatural for an animal that 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. Most treats given to horses are high in sugar, with carrots having more insulin-triggering sugar than apples.

GLYCEMIC INDEX

The glycemic index is a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels. It compares foods gram for gram of carbohydrate. Carbohydrates that break down quickly during digestion have the highest glycemic indexes. The blood glucose response is fast and high. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have low glycemic indexes (12).

In humans the glycemic index of foods is determined by starting with a dose of straight glucose and determining how high the blood glucose goes. Then all foods are compared to that value (which is called 100). So, foods are either higher in number than 100, which is very high in glycemic index, or lower than 100. Low glycemic foods range from 55-69, and these would be desirable for the insulin-resistant horse.

One study that has been done in the horse world uses oats as the baseline and calls that 100 (13). This gives people the impression that oats are high in glycemic index, therefore not a good food to feed EMS horses. However, in humans oats are around 58-69, all in the low to medium range indicating a good food to use. And oats are highly recommended as a source of safe carbohydrates.

SOLUBLE CARBOHYDRATES

As more research is directed towards carbohydrates for humans and horses, it is becoming apparent that many feeds previously considered low in carbohydrates actually contain soluble sugars. This is particularly true of hay, which has been fed without much thought to its energy content. Many high quality hays contain high levels of soluble carbohydrates. In general, horses with EMS laminitis or those that have a tendency to be fat should be fed hays low in sugar. Look for late cut, coarser hays. Different types are available in various parts of the country. Alternatively some of the soluble carbohydrates can be soaked out of the hay. Research is showing that at least an hour will give good benefits to many hays, but will not remove all the sugars from all hays (14). Discard the soak water.

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.

SOY PRODUCTS

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 which is related to carbohydrate metabolism. These sprays 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. The toxicity studies have been done with about one percent concentration. 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

Glucosamine is being fed to horses in large quantities, mostly for arthritis-related conditions. The effects 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 that 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

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 are best to be limited. If treats are fed, apples are better than carrots or molasses-based cookies. A simple grain mix of oats or barley can be used. Barley may be one of the best foods to use with horses who have laminitis. It is considered a cooling feed in Chinese medicine, and laminitis is a hot disease, so barley balances the body. Even when laminitis is not present, many of the Chinese imbalances that lead to insulin resistance are warm in the body.

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 cells more sensitive to insulin so glucose can be taken in 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 (4-8 oz. per day) or naturally stabilized hemp or flax meal (6-8 oz per day) provide EFAs in a therapeutic dose and palatable form. The nutrient inositol also helps with the utilization of the essential fatty acids.

ANTIOXIDANTS
Coenzyme Q 10 clinically seems to be one of the best antioxidants for use in laminitis cases. Horses often become less painful rapidly when Co Q 10 is used without concurrent anti inflammatory drugs. The therapeutic dose is 300-600 mg per day for the first week or two, then the dose can be decreased slowly to a maintenance of about 100 mg per day.
Vitamin C is an excellent antioxidant with doses ranging from 3 to 8 g per day.

CHINESE MEDICINE

Constitutional homeopathy and Chinese medicine (herbs and acupuncture), selected according to the symptoms the individual is exhibiting, are a key to correcting these horses for the long term. It is advisable to work with an experienced homeopath or Chinese herbalist or acupuncturist.

ENVIRONMENT

If it is possible to decrease environmental stress, the horse will benefit greatly. Many competition horses are past their high-stress years, and may not be competing but are feeling the effects of a lifetime of stress.

CONCLUSION

Treat each horse as an individual and seek quality practitioners to help you. Try to recognize the signs as early as possible. When you see horses start to exhibit any of the clinical signs, treatment can be more successful. Enjoy the challenge.

REFERENCES

1. Shepherd PR, Kahn BB. Glucose transporters and insulin action. Implications for insulin resistance and diabetes mellitus. N Engl J Med. 1999;341(4):248-257.
2. Garcia MC, and Beech J. Equine intravenous glucose tolerance test: glucose and insulin responses of health horses fed grain or hay and of horses with pituitary adenoma. Am J Vet Res. 1986;47: 570-572.
3. Beech J and Garcia M. Hormonal response to thyrotropin-releasing hormone in healthy horses and in horses with pituitary adenoma. Am J Vet Res. 1985;46: 1941-1943.
4. Loeb WF, Capen CC and Johnson LE. Adenomas of the pars intermedia associated with hyperglycemia and glycosuria in two horses. Cornell Vet. 1966;56: 623-626.
5. Reed, SM. Pituitary adenomas: equine Cushing’s disease. In: Reed SM and Bayly WM, eds. Equine Internal Medicine, Philadelphia: WB Saunders Company; 1998: 912-915.
6. Zavaroni I, Bonini L, Fantuzzi M, et al. Hyperinsulinemia, obesity and syndrome X. J Int Med. 1994;235: 51-56.
7. Reaven, GM. Pathophysiology of insulin resistance in human disease. Phys Rev. 1995;75(3): 473-485.
8. Neel JV. The “thrifty genotype” in 1998. Nutr Rev. 1999;57(5): S2-S9.
9. Coffman JR, Colles CM. Insulin tolerance in laminitic ponies. Can J Comp Med. 1983;47:347-351.
10. Adamo M, LeRoith D, Simon J. Effect of altered nutritional states on insulin receptors. Ann Rev Nutr. 1988;149-166.
11. Cline GW, Peterson KF, Krssak M, et al. Impaired glucose transport as a cause of decreased insulin-stimulated muscle glycogen synthesis in type 2 diabetes. N Engl J Med. 1999;341: 240-246.
12. http://www.glycemicindex.com/
13. http://ari.calstate.edu/FundedProjects/docs/docs/Glycemic%20Index%20Summary%20Final%20Report.pdf
14. http://www.safergrass.org/

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