Guest Author - Susan Hopf
Equine Cushing’s Syndrome or hyperadrenocorticsm and pituitary pars intermedia dysfunction (PPID) are all different names of the same metabolic disorder that many horses and owners will have to deal with as the equine lifespan continues to increase. Originally is was thought that a slow growing benign tumor of the pituitary gland, that eventually obstructs the pituitary’s ability to function, was to blame but it now seems that stresses from oxidation may be the real cause of this disease process. New research exploring the effects of anti-oxidant supplementation is now underway and may prove to be a valuable ally for the next generation of geriatric horses. Regardless of cause the metabolic ramifications of this disease, which affects so many of our horses, creates unhealthy increases in cortisol levels that can wreak havoc with almost all regulatory systems of the horse as well as in other animals, including humans.
Symptoms that are commonly exhibited by horses with Cushing’s relate directly to the adrenal gland receptors receiving incorrect signals from the failing pituitary and hypothalamus (another gland directly linked to endocrine based hormone shifts in the body). The adrenal glands secret cortisol (a naturally produced steroid) when ordered to do so from the pituitary and hypothalamus. Cortisol controls many bodily functions including but not limited to the body’s ability to regulate insulin, breakdown carbohydrates, fats and proteins, respond to immune stressors and inflammatory challenges and is intricately involved in the body’s ability to repair connective tissue and maintain muscle tone.
Increased drinking and urination, muscle wasting, inappropriate fat distribution (cresty neck), long shaggy coats and laminitis can all be traced back to this failing endocrine hormone system. Add nutritional and environmental stressors and the Cushing’s horse has a difficult battle to wage every day.
There are currently good treatments available. Dietary changes are essential as is good management of the horse’s overall care and health. Put all of these ingredients together and most afflicted horses can remain active and happy for many years past the diagnosis.
Treatment options are as follows:
Pergolide is the current drug of choice. There used to be some concerns of laminitis with Pergolide but the dosing has been corrected and such concerns have been lessened.
Cyproheptadine does not seem as effective as Pergolide and requires a varying dosing schedule. A beginning dosage is calculated and increased until symptoms start to subside – the usual indicators being a return to normal drinking and urination. Once this is achieved and any other symptoms fade away the dose can then be decreased.
There is also a human drug that acts directly on the adrenal gland called Trilostane currently under investigation for use in horses. It acts directly in the adrenal gland ideally controlling the release of cortisol.
There is also some anecdotal success with an herb called Vitex – also called chasteberry it possess the same qualities of dopamine. Some herbal preparations contain additional herbs that are designed to assist with immune boosting and the leveling out of increased endocrine influences.
Most Cushing’s horses need to remain on medications for the remainder of their lives.
As an adjunct to medication good health management is a must. Since Cushing’s stresses the immune system it is vital to eliminate, to the greatest extent possible, any environmental stressors. Maintaining good dental and physical hygiene, necessary vaccinations and a de-worming program are all vital.
Nutrition for the Cushing’s horse becomes all-important and without significant alterations to the diets of these horses most other treatments and considerations will fail. The most important consideration is the level of Non-structured carbohydrates. These are starches and sugars that are too quickly converted to glucose – this causes a surge in insulin and produces deleterious effects on horses whose systems are already stressed. The feed companies are all now producing low starch type concentrated feeds and this is where you should begin your feed search. For those horses whose energy needs are more than these feeds have to offer a supplement that is high in natural fat, like fats from flaxseed, rice bran and soy are all acceptable additions. Supplementation with a good vitamin, mineral and antioxidant product is also recommended.
Early diagnosis and treatment usually results in a better response. Diagnosing can be a bit tricky due to fluctuating levels of cortisol throughout the day as well as throughout the year. There are several blood tests that will confirm the Cushing’s diagnosis. I will caution you here however that if you suspect Cushing’s and the blood tests fail to confirm such I would have a serious discussion with your veterinarian about moving forward with treatment anyway. There are other metabolic disorders that have similar symptoms and if they also come back negative treating for Cushing’s may be a safer move than waiting until the symptoms become worse and the tests finally agree with those increasing symptoms.