For Love of the Horse

Laminitis 101 – “Cushing’s”

We consistently get the argument that a horse has “Cushing’s” and not IR.


The typical look of a “Cushing’s” horse.

I believe it is important to know where the term “Cushing’s” comes from.  It is not an actual disease in itself, rather a term given to horses that fell into a specific “category” based on elevated ACTH levels in blood work.  This is how this disease is diagnosed.  The thing is, ACTH is driven up by elevated insulin levels.  Insulin Resistance (IR) is defined as ineffective/abnormal cellular insulin action response.  This translates, in blood work, as identified hyperinsulinemia (elevated insulin levels).  It has been this way since 1939, there is no other definition. Essentially, this means that when a horse is diagnosed with “Cushing’s” through blood work, this horse has an underlying metabolic condition called Insulin Resistance.   Dr. Thomas’ article, “Take the Guesswork out of Predicting Laminitis”, was written to explain that the metabolic dysfunction in horses leading to laminitis is Insulin Resistance (IR), NOT Cushing’s and not EMS.  In his article, Dr. Thomas brought up a recent investigation into the risk of laminitis.  Researchers placed horses into groups that were “Cushing’s” (elevated ACTH), EMS (physical signs: fat deposits/cresty neck) and IR (elevated insulin).  It was not mentioned in their article that every horse in the study, regardless of the diagnosis, had elevated serum insulin (IR).  ¼ of these horses had reached the end result of IR (type 2 diabetes with compensatory hyperinsulinemia; elevated glucose/elevated insulin), and these horses were assigned to the Cushing’s group.  The underlying problem? IR.

The most common answer for a diagnosis of “Cushing’s” is Pergolide (Prascend).  The problem with this drug is that it ONLY reduces ACTH levels within the very early stages of being given.  Research has proven that Pergolide will not lower insulin nor will it have any effect on the frequency or severity of a laminitic episode.  This drug has been banned by the FDA, TWICE, for its dangerous side effects.  I cannot tell you how many people come to us after “X” amount of time their horse has been on Pergolide.  It seemed to work for a while, but now their horse is back to square one.  This is scary and worth considering if your horse IS on Pergolide.

Even if your horse has been diagnosed with “Cushing’s”, they still can be helped.  They need the same changes as an IR horse, as the IR is the root of the problem.