Cushing`s or Not, Attack Insulin Resistance

People who own horses with Cushing’s or other metabolic problems, like insulin resistance, struggle with watching their horses go downhill, often with the high cost of medications. Though research is ongoing about these metabolic problems, we decided to take a different approach to see if we could make a difference in these horses’ lives through diet, which is the first line of attack physicians use with people who have insulin problems. Diet and exercise may eliminate the need for medication in insulin-resistant people, if they follow the recommendations, and it works even better in horses because they can’t cheat.

Don’t guess: Get the right tests done. True Cushing’s involves a pituitary tumor that may result in a long coat that won’t shed out. Treats count, too, in your horse’s dietary management.

If a horse truly has Cushing’s disease, he has a pituitary tumor, which eventually leads to insulin resistance. In recent years, however, vets have been calling similar conditions with no real evidence of Cushing’s disease “pre-Cushing’s” or “peripheral Cushing’s.” While these are nothing more than labels, the terminology has lead to an unwarranted use of the pricey drug pergolide (see page 13). We think that, unless the horse has a pituitary tumor, giving him this type of tumor-suppressing drug may not be the first route to take.

The fact is that a horse can be insulin-resistant without having true Cushing’s disease.

A purely insulin-resistant horse does tend to be an easy keeper, with a cresty neck and possibly abnormal fat deposits — like Cushing’s horses — but he may be much younger than true Cushing’s horses, having no classic symptoms of Cushing’s and no laboratory evidence to confirm it.

Early cases of both Cushing’s and insulin resistance may go unnoticed. The horse may then progress to become lethargic and overweight, often developing laminitis. This is when concerns peak, and sorting between Cushing’s and insulin resistance becomes critical to determining the best treatment options.

In Cushing’s, the cells become insulin-resistant because of the inappropriately elevated levels of the hormones produced by the pituitary tumor. The causes for insulin resistance in non-Cushing’s horses are less clear and may involve other hormone imbalances or thyroid problems or a genetic tendency.

Uncorrected, the insulin resistance may worsen and the pancreas can become incapable of putting out enough insulin to drive the glucose into the cells, causing blood sugar to remain elevated. This in turn causes high outputs of urine as the kidneys try to clear the extra sugar in the blood, and abnormal thirst in response to the high urine output. In the final stages, the pancreatic output of insulin can drop to abnormally low levels and glucose continue to rise, at which point the horse becomes truly diabetic with insufficient insulin. Muscle atrophy and weight loss set in, as the cells can’t be correctly nourished when the glucose can’t get in.

Cushing’s disease is a complicated syndrome, involving several hormonal systems. And when hormonal systems are involved, there’s really no simple cause and effect. What affects one branch is likely to have repercussions in the others as well. Elevated levels of cortisol and other hormones can cause insulin resistance. Thyroid abnormalities can also be related to insulin resistance, whether or not Cushing’s is truly present. Thyroid problems are difficult enough on their own, but the matter is further complicated with insulin resistance.

Some veterinarians question the reliability of thyroid-function tests in horses. However, we found several horses with lab-confirmed insulin resistance and no other evidence of Cushing’s disease that had abnormally low levels of T4 (the inactive hormone), T3 (the active thyroid hormone) or both.

In January 2001, when we tackled the effect of magnesium supplementation on overweight, cresty, laminitic horses, we were surprised by the excellent response in our trials. Our article also generated letters from readers who shared additional success stories of its effect with a visible reduction in cresty necks. Intrigued, we decided to dig deeper, looking at insulin resistance in horses, its possible causes, and how diet and supplements might affect it.

Our Field Trials
When we began looking at horses with insulin resistance, we quickly found many were called Cushing’s without clear evidence to support it. We requested that each owner send us a hay mineral analysis. The reviews showed several minerals lower than National Research Council recommendations and/or present in amounts that led to less-than-optimal ratios between minerals. It’s difficult to make a generalization about these findings for your hay, but we can tell you that these hays were a variety of grass hays from different areas of the United States.


Based on this information, we put the horses on a custom mineral mix for their hay or on a supplement we formulated to cover the most important deficiencies and imbalances related to both insulin function/production and the thyroid. Our mineral formulations were mixed by Uckele Health and Nutrition (800/248-0330 or at the website, but you can contact your own local feed mill or mix what you need from individual supplements. We then followed the horses, noting changes in clinical response and in blood work.

These horses were all on either pergolide, cyproheptadine or Hormonise when confirmed Cushing’s cases, had hay-only or hay-and-beet-pulp diets. Drops in insulin were observed in all cases that had mineral intakes balanced. In some horses, like Frosty (see case history below), the correction was complete.

Even longstanding Cushing’s horses can show improvement with mineral correction, as did a pony on pergolide whose insulin remained high at 300 but dropped to 70 with mineral correction. However, blood results don’t always improve to the same degree.

One aged Arabian mare in our study had her first bout of laminitis in 1995 and was documented with clearly abnormally high blood glucose as early as 1997 but not confirmed as a Cushing’s case until 1998. She was treated for about a year with cyproheptadine but switched to Permax when response to cyproheptadine was poor.

When first evaluated for the trial, the mare had glucose levels of 500 to 1000 mg/L in her urine (it should be zero), a blood glucose of 135 mg/dl on a hay diet (should be less than 100), and her insulin was 97.5 mU/ml (top normal of 30). She also had low T3 and T4, despite thyroid supplementation.

On the first version of a mineral mix formulated for insulin resistance/hypothyroidism, her insulin dropped to 65.8, blood glucose to 94 and her urine glucose ran about 250. Her T4 was now normal, but T3 remained low. When switched to another version of the insulin resistance/thyroid mineral supplement, with higher levels of iodine and selenium, her blood sugar dropped to 84, urine was 0 to 250, and T3/T4 were normal.

Two mares — ages 13 and seven, a mother and daughter — had suffered from severe laminitis and also had the typical abnormal fat deposits. They worsened on a high-protein diet with high-calcium supplements. Their owner had them on pergolide and was making some mineral adjustments to the diet when she had a dietary analysis done and a custom mineral supplement formulated.

The combination of me dication and mineral adjustments resulted in improvement in their weight and resolution of the laminitis, but insulin levels were still over 100. Enter adaptogens.

Adaptogens are so-named because of their ability to help the body adjust/adapt to stress of any kind and to restore normal balance to hormonal responses that are either abnormally high or abnormally low.

In another trial, we were seeing energizing effects in stressed horses when they were on Advanced Protection Formula (APF) from Auburn Labs ( 877/661-3505).

We knew some of the advanced Cushing’s cases in this trial were severely depressed, and we found that at least one of the herbs in the APF, eleutherococcus (Siberian ginseng) was reported to stabilize insulin/glucose levels.

The mother and daughter mares were doing well symptomatically but still had elevated insulins of 105 (the older mare) and 155 with glucoses in the high normal range at 105 and 114 on hay only. Both were started on APF. Six weeks later, the insulins were normal at 28.8 and 40.9 (upper normal 42), glucoses normal at 92 and 86. Since then, both were taken off APF and pergolide, with the younger mare continuing to do well with just mineral balancing, while the older mare developed signs of laminitis again that aren’t responding well to pergolide and diet alone yet.

One of our favorite cases was an aged miniature mule with Cushing’s who was going downhill rapidly with chronically painful feet, appetite extremely poor and little energy. She would only slowly amble a short distance from her shed to a manure pile where she habitually lay.


The possibility of euthanasia had come up. The old girl had enough spunk left to adamantly refuse her supplements though, making it really hard to treat her. She had been on cyproheptadine for years, and she had markedly elevated insulin levels for years.

When started on APF, her insulin was 249. At 10 days, it had shot up to over 500, although she was looking brighter. When retested at 30 days, it was all the way down to 73. Our miniature mule was improved, eating much better, walking around the pasture and much brighter.

Another rewarding response was in an aged Paso Fino gelding, also failing rapidly and facing euthanasia. He had been treated for presumed Cushing’s disease with hormone implants and responded well at first but became resistant.

The gelding couldn’t be persuaded to leave his stall. His insulin at this point was 159 (upper normal for the laboratory was 20). Four days after starting the APF, his thrilled owner reported he had walked 450 feet on his own and willingly ventured out into his paddock.

Within a week, he was spending several hours in the paddock and the owner saw him gaiting in response to her calling him. This horse has progressed to the point he is now being ridden again. The insulin/thyroid mineral supplement was started about two weeks after APF began. The first repeat insulin, three weeks after starting APF, was down to 104. Repeat after 2.5 months, with both diet changes and APF, was 95. The laminitis was better.

Bottom Line
Horse owners should avoid the trend of lumping all fat, hairy, laminitic horses into one giant “Cushing’s” category and simply treat the problem at hand. If it’s insulin resistance, then these horses need to have strict dietary management.

If it’s true Cushing’s disease, these horses need medication, plus dietary management. We believe the dietary management is critical to these horses. We found balancing the horse’s dietary mineral intake could help correct insulin resistance, in both Cushing’s disease and in non-Cushing’s cases, and could help correct any thyroid hormone deficiency the horses had.

In addition, we found supplementation with APF can result in significant improvements in blood insulin levels, laminitic symptoms and overall energy and appetite.

Also With This Article
Click here to view ”Control Insulin Resistance.”
Click here to view ”Know What Cushing’s Terms Mean.”
Click here to view ”Frosty: A Story Of Determination.”
Click here to view ”Be Cautious With Pergolide.”
Click here to view ”Minerals: Proper Dietary Management.”