EQUINE CUSHING’S SYNDROME

This condition is an endocrine disorder that affects older horses. It is caused by dysfunction of an area of the pituitary gland, which is situated at the base of the brain. This increases in size due to formation of a type of tumour, causing it to secrete more hormones than normal. The variety of hormones it secretes and amounts of each, affect the complex array of clinical signs we see in individual horses. Due to the pituitary gland’s location near the optic nerve, vision can also be affected.

Although not exclusive for Cushing’s, indicators we see include:
> usually an older horse
> thick, long and wavy haircoat (winter coat) that fails to shed as the weather warms.
> weight loss and muscle wasting
> excessive urinating and drinking
> more docile and lethargic
> abnormal bulging in fat pads present above the eyes
> increased respiratory rate and effort
> persistent sweating
> repeated bouts of laminitis
> vision problems
> repeated skin, lung, urinary or sinus infections

A horse may have one or more of these conditions when they have Cushing’s.

Lowered immunity makes affected horses more prone to conditions such as worm infestation, pneumonia and tooth infections. Liver failure and bleeding disorders can also occur, and horses may seizure.
Depending on the clinical presentation, diagnosis of Cushing’s Syndrome often involves performing a dexamethasone suppression test. This involves taking a base measure of plasma cortisol concentration and then injection the horse with dexamethasone (a cortisone) and the taking a second sample the next day. Plasma cortisol levels remaining high up to 24 hours after administration of dexamethasone is indicative of having Cushing’s.

Treatment of Cushing’s involves maintenance of the aging horse’s overall health, so we ensure they have a good diet of quality feed but avoid grain or overfeeding high-energy hay. Worming is important, as is maintenance of teeth and hooves, especially with the risk of laminitis.

Oral pergolide (a human medication) is most often used to manage Cushing’s Syndrome. After 6 weeks of treatment, improvement should be seen by less drinking and urinating, shedding of the hair coat and reduction in blood glucose levels. Repeated blood tests may be required to monitor the improvement and whether the drug dose needs to be altered. A key element in deciding to treat Cushing’s is the cost, as long-term treatment can be expensive. If you have any concerns about your older horse, please contact a Riverdene vet for advice.