Equine Cushings Syndrome

Following the recent tragic loss of wonderful Victory Salute to laminitis, caused from Equine Cushings Syndrome, we decided to find out more about this terrible affliction.

What is it?

Equine Cushing’s Syndrome (ECS) has been documented to affect more than 10% of horses over 15 years of age (McGowan, 2003). While the condition is known to affect all horses, ponies have been reported to be more likely to develop ECS (McGowan, 2003). The average age of diagnosis is 19 years while it is rarely seen in horses less than 10 years of age (McGowan, 2005). 

What are symptoms?

Symptoms of ECS include hirsutism (excessively long hair, failure to shed hair in the spring and summer), lethargy, muscle wasting, bulging supraorbital fat pads, recurrent or chronic laminitis, susceptibility to infections such as recurring sole abscesses and polyuria (excessive urination) /polydipsia (excessive thirst).

Abnormal fat distribution is one of the most common clinical signs among horses suspected of having ECS, including fat deposition in the crest of the neck or the dorsal aspect of the back and tail head. This clinical sign is in contrast to simple obesity in horses in which fat is deposited around the neck, back, tail head, ribs and flank and caudal to the triceps (Donaldson et al., 2004).

Laminitis is frequently the most devastating clinical sign with severely affected horses requiring euthanasia, although in some cases, laminitis does not develop at all.

What is the cause?

Equine Cushing’s Syndrome (or otherwise known as Pituitary Pars Intermedia Dysfunction) is caused by hypertrophy (excessive growth), hyperplasia (abnormal multiplication of cells) and (micro) adenoma (benign tumor) formation in part of the pituitary gland (the pituitary pars intermedia) which results in an increased secretion of certain hormones (particularly ACTH, or adrenocorticotrophic hormone) creating an imbalance in the body.

Horses with Cushing’s Syndrome develop enlarged pituitaries to as much as five times the normal weight. As the pituitary pars intermedia expands, it compresses the adjacent lobes and hypothalamus, often resulting in a loss of function of these tissues. The pituitary pars intermedia remains active, secreting large amounts of excess hormones into peripheral circulation. Resultant excess hormones include large amounts of ß-endorphin, corticotrophin-like intermediate peptide (CLIP) and melanocyte stimulating hormone (MSH) and smaller amounts of adrenocorticotrophic hormone (ACTH) (McGowan, 2005). Horses may have as much as 40 fold increase in plasma concentration of these hormones (McFarlane, 2006).

Is there a treatment?

Cushing’s Syndrome is the most common endocrinopathy of horses, which, to date has no therapeutic product registered specifically for animal application. Pergolide mesylate is an ergot dopamine receptor agonist at both D1 and D2 receptor sites. It has been sold in Australia for human use as an anti-Parkinson’s Disease therapy as the TGA registered drug PERMAX (Eli Lilly). Off label use of pergolide mesylate by veterinarians has been frequent in recent years, where the drug has been described as the “treatment of choice” for ECS. Pergolide works by binding with drug receptors in the brain that control the production of dopamine in the hypothalamus. Therapy of horses has consisted of either human pergolide mesylate tablets crushed for oral use, or compound pharmacy products produced from human product raw material. There is currently no pergolide product registered for veterinary application.

How is it managed?

Good husbandry and awareness of potential complications of ECS are essential in the management of this disease. Affected horses should receive regular dental and foot care, deworming and good nutrition. Horses with hirsutism should be clipped to prevent heat stress and dermatologic problems associated with sweating.

As with many chronic diseases in the horse, specific dietary formulation is recommended. Meals high in non-structural carbohydrates (NSC) such as grains and molasses should be avoided. Pastures can also contain high levels of starch and fructan and access should be limited. Carrots and apples also have relatively high levels of NSC. In general, feeds low in NSC include soyhulls, sunflower seeds, cottonseed meal, lucerne hay, and beet pulp, however some of these feeds can be unpalatable and require processing. For more severe cases, hay may be soaked in double its volume in lukewarm water for 1 hour then drained before feeding to remove soluble sugars and NSCs. Many people put affected horses carrying extra weight on a “starvation diet” and severely limit the horses’ diet of all nutrients. This will only make matters worse as the horse still needs maintenance energy to function as well as essential amino acids, vitamins and minerals, particularly if laminitis is present. Both magnesium and chromium supplementation have been advocated for supportive treatment of this condition (Schott, 2006).

This information was extracted from an article at www.ranvet.com.au that includes a much more comprehensive description of methods of diagnosis and treatment, and links to sources. Follow the link to find out more, however, if you suspect your horse could have Equine Cushings Syndrome, consult your vet.

Ranvet 500 PLUS is a superior protein supplement containing high levels of minerals and is low in NSC. This supplement is ideal for ECS ponies and horses in combination with chaffs and hay. Balanced oils, such as Ranvet’s Grand Prix Oil may also be added as a source of energy if required.

 

For further assistance in a custom diet formulation for ECS cases, please feel free to contact Ranvet on 1800 727 217.