Cushing’s what is?

Cushing’s..Chaste Tree and Adaptogens can help by James Hart of Equine Herbals

As our horses are living longer and we are becoming more concerned for their welfare it is not surprising that we are seeing an increasing incidence and awareness of diseases associated with middle and old age. Two of these are Cushing’s Disease and Insulin Resistance. These are related endocrine disorders with similar presenting symptoms but totally different physiological changes. This article will mainly discuss Cushing’s.

What is Cushing’s?

Equine Cushing’s disease is caused by a dysfunction of the pars intermediary portion of the pituitary gland which results in hormonal imbalances. For this reason it is also known as PPID – pars pituitary intermedia dysfunction. Cushing’s is probably easier. These hormonal imbalances in turn cause the symptoms that are becoming increasingly familiar and include the long wavy coat that fails to shed in the spring, excessive sweating, lethargy, poor athletic performance, chronic recurrent laminitis, infertility, weight loss, muscle wasting, abnormal fat distribution; especially on the neck and tail head, excessive drinking and urination, and enlargement of the mammary glands.

Combined with the visible symptoms described above you will usually find a depressed immunity. This can lead to increased infections, possibly skin sores and increased susceptibility to internal parasites. Depression of the immune system is probably caused by the hormonal imbalances and is likely to be made worse by the general poor condition.

What is Insulin Resistance?

The main symptoms of Insulin Resistance (IR) are sluggishness, a tendency to gain or loose weight easily, the appearance of a cresty neck, fat in the eye hollows and other fat pads. There can also be a tendency to hoof problems including laminitis. Insulin is produced by the horse’s pancreas and is needed to help control the levels of glucose in the blood. More horses seem to be genetically predisposed to IR than show it. Things that may trigger the condition to appear include include high-carbohydrate or high-fat diets, mineral deficiencies, lack of exercise, obesity, and stress.

You may see references to another condition called Equine Metabolic Syndrome. This is the same thing as Insulin Resistance, which has become the preferred name.

Cushing’s Disease.

Cushing’s is one of the most common conditions in older horses and can occur in all types and breeds of equids, not just horses. It is most common in ponies and Morgans. It can affect them earlier but most sufferers are over 15 years of age. Once they get to this age as many as 30% of horses are likely to be suffering from Cushing’s. It is a progressive condition for which there is no cure. An abnormal growth in the pituitary causes the overproduction of adrenocorticotrophic hormone (ACTH). The surplus ACTH spurs the adrenal glands to manufacture excessive cortisol, a hormone that can negatively impact numerous body systems.

If your horse is showing some of the signs noted above then suspect Cushing’s or IR.

The following table shows the distribution of symptoms of 159 Cushing’s individuals;

Long, non shedding coat 80%
Muscle wasting 60%
Chronic laminitis 50%
Increased urination 40%
Excessive sweating 30%
Abnormal fat deposits 25%

The signs of Cushing’s, which you will not be able to see, may be diagnosed by your vet. These may include increased PMOC, a depressed immune system, oxidative stress, reduced dopamine levels, insulin resistance and increased beta-endorphin in the spinal fluid. Unfortunately accurate diagnosis is still difficult and but is important to decide whether you are dealing with Cushing’s or IR. There are a number of ways of testing for Cushing’s. The two most practical and accurate tests currently available are (1) the dexamethasone suppression test, and (2) measurement of plasma ACTH concentration. A new test has just been announced in the USA based on  omperidone stimulation. It is not available yet but could prove to be useful in picking early Cushing’s.

The dexamethasone suppression test is an overnight protocol in which a pretreatment blood sample is collected in the late afternoon. A low dose of dexamethasone is then administered by intramuscular injection. A second sample of blood is collected the following day at around noon and both samples are submitted for measurement of plasma cortisol. In normal horses, administration of dexamethasone stimulates a negative-feedback response that suppresses secretion of cortisol from the adrenal glands. There should therefore be a much lower concentration in the second blood sample. In horses suffering from Cushing’s disease, however, the negative-feedback response is blunted and a lesser degree of suppression, if any, is observed.

Although it still the most widely used the dexamethasone suppression test has drawbacks that limit its use: it requires two visits to the farm by the vet, which increases its cost to the owner, many owners and vets fear that administration of dexamethasone might increase the risk of laminitis in a horse that is already predisposed to its development. The test may also be unreliable in the autumn in mares due to normal hormonal changes bought on by the change in season. For these reasons, there is an increasing move to the measurement of plasma ACTH. This test involves collection and analysis of a single blood sample; the pituitary gland in affected horses often secretes excessive amounts of ACTH into the bloodstream as compared to normal horses. While useful, this test is sometimes considered to be less accurate than the dexamethasone suppression test, and blood samples must be handled very carefully to avoid degradation of ACTH and falsely low measured values. In human and canine Cushing’s the ACTH test is considered the gold standard. There is still uncertainly in the equine world as to which is the best.

Treatment options.

Although there is no cure there is quite a lot we can do to help improve or maintain quality of life of a Cushing’s sufferer. There are two prescription drugs commonly prescribed. These are pergolide (trade names Permax) and cyproheptidine, but both have some reports of side effects.

From a herbal perspective there are several things we can do to help maintain or improve a horse’s quality of life. Chaste Berry (Vitex agnus-castus) has a long history of use in female hormone imbalance. Its action in the brain is also similar to pergolide, in that both bind to dopamine receptors. There have been a number of trials on Cushing’s suffers using Chaste which have demonstrated mixed results. This may well be because the preparations used have been of unspecified strength. It is therefore impossible to know how much of the herb has actually been given. I read one report of a researcher being told by the company making a Chaste Berry preparation that the strength of the extract was commercially sensitive and that they would not disclose it. Interestingly the same company told me they didn’t know the strength of their extract. We have been using Chaste on Cushing’s cases for some time and although it doesn’t work in all cases the results have been very encouraging. We have typically been using a dose of 20ml twice a day of a 1:2 extract.

Alongside Chaste other herbs to use should depend on the individual case. For example, Echinacea or Cat’s Claw are often used to support the immune system and Devil’s Claw or Boswellia are useful when anti inflammatories are called for.

The whole question of the treatment of endocrine disorders is difficult because a small change in hormone levels can have a significant effect. Also the interrelationship of the different hormones is very complex and in some cases not yet fully understood. In conventional medicine the extremely delicate balances and small amounts of hormone necessary to effect change make treatment difficult. The plant world however gives a class of herbs known as adaptogens. These are herbs that supplement the body’s ability to deal with stress. This can be from anxiety, fatigue, or trauma which in turn often results in stress on the endocrine system. Using the problem of Cushing’s as an example.

The lack of domapine stimulates glucocorticoid production by the adrenal cortex. The normal feedback mechanism has failed so glucocorticoid production becomes excessive resulting in stress on the adrenal cortex. Adaptogens are not one small type or predetermined mixture of herbs, but a variety of plants that may be used alone or in combination. It is thought that these herbs promote the balancing of the endocrine (hormone) system and boost the immune system. In this way they help promote and maintain homeostasis; the state of balance and stability in the body.

There is a fairly wide range of adaptogens including some commonly used herbs such as Ashwagandha (Withania somnifera), Astragalus (Astragalus membranaceus), Siberian Ginseng (Eleutherococcus senticosus), Licorice (Glycyrrhiza glabra) and Schisandra (Schisandra chinensis).

There are a couple of things that are also useful and easy to do. The oxidative stress can be helped by adding antioxidants to the diet. These are readily available; one of the best is Rosemary. It can be fed fresh or dried at a rate of about 30gms a day. Fenugreek is a herb that is easy to include in the diet. It has been well researched and has shown promise in the management of blood sugar levels and insulin in other species, but no direct work has been done on horses. The soluble fibre in Fenugreek seeds slows sugar absorption and we know that it helps to maintain condition. It is generally known that aging in humans causes changes in the gut. The most notably is decreased gastric secretions and therefore decreased digestive efficiency. It is also believed aging may adversely affect digestive function in horses. One study showed digestibility of protein, fibre and phosphorus were lower in horses aged over 20

Things to Avoid


It may be necessary for a horse with acute laminitis but it should be used with great caution and only under the direct instruction of your vet. If it is used on Cushing’s horses it can cause additional problems. For minor aches and pains or chronic problems like arthritis, the use of Devil’s Claw or Boswellia are better options.


Yucca affects insulin and glucose levels and may increase problems for horses with a history of laminitis or insulin disturbances.

Carbohydrates like grain and molasses.

As carbohydrates are digested, large amounts of glucose enter the bloodstream. Elevated levels of circulating glucose can alter secretion of cortisol, thus negatively affecting metabolism and possibly contributing to the symptoms of Cushing’s and triggering laminitis.  Feed higher fibre in diet such as alfalfa meal, soy hulls, beet pulp and if more energy is required then oils can be added but care should be exercised as the feeding of oils have been associated with the development of insulin insensitivity. was in horses less than 10. Fenugreek is also mildly bitter and therefore stimulates gastric activity. Something needed in older animals.

Unfortunately Cushing’s seems to be becoming more widespread but since the death of Barbaro from severe laminitis there has been a big increase in the research effort into laminitis and Cushing’s and perhaps better understanding of these difficult problems will emerge.

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