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Diet Recommendations for Equine Cushings and Cushings-Like-Syndrome, AKA Insulin Resistance

Cushings Disease is caused by a loss of the dopaminergic neurons of the hypothalamus. These neurons, which descend into the pars intermediar of the pituitary, have a role in limiting its growth. The loss of the neurons means that the pars intermediar grows larger and increases its output of Adreno-Cortical Stimulating Hormone (ACTH). In turn, this causes an overproduction of the natural steroid, Cortisone. The symptoms include an unusually thick coat that does not shed out in hot weather, loss of muscle tissue, impaired ability to heal and fight off infections, weight gain in the neck (cresty neck), fat deposits which appear on the shoulders and tail head, and a tendency to founder.

In recent years, we have begun to recognize another condition that looks a lot like Cushings, but it occurs much earlier in life. Although many of the symptoms are the same, these horses do not have the excessively high ACTH levels. These horses with Cushing-Like-Syndrome often turn out to be insulin resistant (IR). This is similar to a kind of equine Type II Diabetes, a condition where the muscle cells are unable to absorb glucose due to an inability to respond to the hormone Insulin.

To differentiate between the true Cushings horse and the IR or Cushings-Like-Syndrome horse can take a lot of work. The IR horse has all or some of the same symptoms as the Cushings horse, but does not have the high ACTH level. Simply checking for blood levels of ACTH does not always provide the answer. This is because ACTH naturally increases in the fall, to help prepare the horses body for the oncoming winter. Thus, doing an ACTH level in the fall months will give a false positive for true Cushings.

The best way to tell them apart is to perform a Dexamethosone Suppression test or a Glucose Tolerance test. Both of these measure the actual tissue response to administered steroids (Dexamethosone) or glucose. However, both of these tests need to be done by a veterinarian, and both have their limitations.

Why is it important to know the difference between the syndromes? After all, apart from drug intervention, we treat them both the same way. Because if the veterinarian diagnoses Cushings, they will normally prescribe Pergolide or Cyproheptadine, which is expensive and not effective if the horse is actually an IR horse. Also, like all drugs, they can have side effects, so make sure they are necessary before administering. The IR horse is usually treated by diet alone.

Then, there is the question of long term survival. The true Cushings horse will need drug intervention at some point, so you need to know if this scenario is on the horizon. The IR horse may never need drug intervention, but will need to have his diet closely monitored.

For Insulin Resistant horses, some veterinarians will prescribe Thyro-L, which is a manufactured form of thyroid hormones. Thyro-L acts to increase the basal metabolism, and also helps the action of insulin to clear glucose from the bloodstream. Some horses have done well on Thyro-L supplementation for years with no apparent side effects. Not all horses will respond well to Thyro-L administration, so it is useful to have other dietary supplements available to be used with, or instead of, Thyro-L.

Dietary intervention helps for both syndromes, but there is no cure for true Cushings. The diet will minimize the symptoms, but does nothing for the loss of the neurons, though the Pergolide does replace some of the lost dopamine. The IR horse should normalize with dietary changes.

Diet Can Help:
Firstly, I recommend that the horse should go onto a Low Glycemic diet. In other words, a diet low in simple carbohydrates. This diet is primarily hay, sugar beet pulp, soy hulls, or whatever you can find that is high in fiber and low in simple carbohydrates. Avoid feeds high in sugar (i.e. molasses) or grains (corn, oats, barley, etc.). There are a number of low starch commercial feeds available these days, and you can find one if you ask at your local feed store.

If you cannot find a low starch feed, or if your horse does not respond to the commercial feeds, then you will need to make your own low glycemic feed. To do this you will need a high fiber, low starch base such as sugar beet pulp or soy hulls. To that, you add whole flax seed, 1-2 cups per day, and a good protein/vitamin/mineral supplement. I recommend LinPro™, but any high-quality supplement will do. Ideally, the supplement should also supply essential fatty acids and essential amino-acids.

If the horse cannot maintain a good body condition on the high-fiber diet with the protein/vitamin/mineral supplement, then you need to add more calories as fat. The best fat sources are oil seeds like flax, whole roast soy, or rice bran, in the least processed form possible. I do not recommend large quantities of any kind of oil as this is a highly processed form.

The bulk of the low glycemic diet should be grass hay - not too fresh and green - older, coarser hay is the best. These horses need have to have their access to green grass severely curtailed. This could mean a dry lot or a grazing muzzle, but either way, limit or eliminate access to green pasture. Once the grass goes to seed and turns brown, as in the heat of summer or dead of winter, then it is safer to allow some closely monitored grazing time.

Dietary (non-drug) supplements that have some use include:
Chromium: This is a mineral that has also been shown to enhance glucose clearance by assisting insulin. Therefore, giving extra Chromium can be helpful. Chromium can be supplied as the proteinate (Chromium Piccolinate) or as Chromium- enriched yeast. The Chromium Piccolinate is the only legal form available to USA manufacturers. Equine nutritionists do not currently know the exact daily requirements for horses. All the amounts currently used (7-14 mg per day) are either based on the limited research work done in swine, or simply guesswork.

Magnesium: This is another mineral which has the effect of relaxing the small arteriols and preserving peripheral blood circulation. Also, in humans, it has an effect of reducing C-reactive protein (an inflammatory marker). Therefore, giving extra Magnesium will help peripheral circulation, and reduce low chronic inflammation.

Increase the horse's Magnesium intake up to 2 grams per 100 pounds of bodyweight per day (i.e. 20 grams of Magnesium for a 1,000 pound horse). Ideally, in conjunction with this, increase the Chromium as well, to 7- 14 mg per day for the 1,000 pound horse. You will need to adjust these numbers accordingly for significantly different body weights. Most importantly, the Magnesium intake is the key component. I prefer to use Quiessence™, which is a supplement that contains Magnesium as a chelate and Chromium as a proteinate. If you cannot get Quiessence™, then use Magnesium Oxide or Citrate as a substitute. You can get Chromium supplements at the drugstore in human form or from your veterinarian.

Keep the horse on the high Magnesium and Chromium until you get a reduction in the thickness and size of the fat deposits on the neck and shoulders. This normally takes 4-6 weeks or more. In about 70% of the horses, you also see an improvement in length of stride and soundness. However, not all horses respond the same, and to the same degree. Once you get the horse to a more normal appearance, then you can drop the Magnesium levels to 10 grams per day, UNLESS the neck starts to build up again. If the neck does enlarge again, increase the Magnesium intake back to 20 grams per day. Use the neck thickness to guide you in adjusting the Magnesium intake.

Herbals: There are several herbs which have positive effects on glucose clearance and/or on pituitary function. None of these have any scientific evidence in horses, though some of them have a few studies in humans and lab animals.

Chastetree Berry has a reputation for being useful for pituitary function.

Alpha Lipoic Acid (ALA) is used an as anti-oxidant, and has a reputation for assisting glucose clearance in humans.

Vanadium has been found in human research to stimulate glucose clearance.

Zinc is used as an anti-oxidant, and is closely involved with Selenium metabolism. Human diabetics have depleted Zinc supplies - thus it may be useful to supplement IR horses with this mineral as well.

Bitter Melon (Momordia Charantia), Fenugreek, Jiagoluan (Gynostemma), and Cinnamon are all thought to help with the regulation of blood sugar in humans and can be found in different human supplements on the market.

I recommend Cush-Alleve™, which has some of the above ingredients, but there are also several other equine products available with different combinations of these herbs.

SUMMARY
In summary, increase the horse's Magnesium intake, if possible in conjunction with Chromium, and reduce the level of simple carbohydrates in the diet. Use a good quality protein/vitamin/mineral supplement, ideally one that also supplies essential fatty acids and essential amino-acids. If this does not provide enough benefit, then try some of the herbal preparations, such as those which contain Chastetree Berry and/or some of the other herbs mentioned above.


Melyni Worth, Ph.D.
www.FoxdenEquine.com

Dr. Melyni Worth Ph.D. - 2007 (c)

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