What is Cushing's disease?
Pituitary Pars Intermedia Dysfunction (PPID) is the correct term for the disease commonly known as Equine Cushing's Disease. Once considered a rare hormonal disease it is now thought to affect 20% of horses over the age of 15, with the risk of developing the disease increasing directly with age.
The disease is caused by changes in the pituitary gland which is located at the base of the brain. The pituitary gland is regulated by a substance called dopamine and produces a variety of hormones which are distributed around the horses body via the bloodstream. These play an important role in maintaining and controlling a variety of body functions.
Horses with Cushing's disease don't produce enough dopamine which means that the pituitary gland is unregulated, and produces too many hormones including Adrenocorticotropic hormone (ACTH).
Sign's to look out for
- Hypertrichosis (long curly hair coat) is a common symptom which is characterised by failure to shed a long curly hair coat, which may become thin and long.
- Increased water intake and urination (polyuria/polydipsia) is one of the most common complaints and can occur in up to a third of horses.
- Laminitis can be seen in horses with pituitary dysfunction.
- Lethargy or a more docile temperament.
- Excessive or inappropriate sweating.
- Recurrent infections such as foot abscesses, tooth root infections and sinusitis occur more commonly in horses with Cushing's compared to normal horses of the same age because some of the hormones released with the condition suppress the immune system.
- Loss of muscle mass, especially over the hindquarters.
- Abnormal fat distribution such as a pot-bellied appearance and fat pads around the eyes.
How is it diagnosed?
Early diagnosis and treatment of Cushing's is important to help deliver the best outcome, but early stages of the condition can be slow to appear making it difficult to detect.
Specific diagnosis of Cushing's requires measurement of hormones in the blood which will be carried out by your vet taking a basal or resting ACTH rest. The results of this test can be compared to reference ranges (which will change with seasons) to confirm diagnosis. However, sometimes the results can be unclear with neither a clearly positive or negative result making a diagnosis difficult. If this is the case your vet may recommend re-testing after a 3 - 6 month period.
How to deal with it
Fortunately there is veterinary medicine available in the form of pergolide which is licensed for the treatment of clinical signs associated with Cushing's. This treatment, which is available from your vet, helps to normalise hormone secretion from the pituitary gland into the bloodstream. The dose rate is dependent upon each individual horse as it depends upon the ACTH levels and the improvement in clinical signs, but it usually takes around 4 - 12 weeks to show any clinical benefit.
Extra attention should also be given to horses with Cushing's who will often regular dental care, hoof care and parasite control along with regular monitoring of basal hormone levels such as ACTH to ensure appropriate pergolide treatment levels. Some horses may also require regular clipping of unnecessary hair in warmer months and may also require a rug in the winter months, to help maintain body condition.
Can the diet help
As many horses with Cushing's develop insulin resistance they may need to be managed in such a way as horses with Equine Metabolic Syndrome (EMS).
Easy keepers that gain, or maintain weight with very little feed require a low energy diet such as Rowen Barbary Forage 'n' Fibre that will help supply all the essential vitamins and minerals to balance the forage given, whilst keeping energy and calories to a minimum. As it contains no cereals and is very low in starch and sugars it is recommended for horses with EMS. Choose stalkier hay that offers a lower nutritional value and it is a good idea to consider soaking it before feeding as it has been found that soaking hay for up to an hour can eliminate 56% of its water-soluble carbohydrates.
If a lot of grass is available strip grazing will help limit the horses total grass intake as will periods of turnout in a grazing muzzle. A diet that contains non-structural carbohydrates (NSC), which include the sugar and starch content in horse feeds, of less than 12% on average per feed is recommended to control the blood insulin levels and help prevent the risk of laminitis developing.
Where fibre alone is not sufficient to meet the energy requirements oils and fats should be added to the diet to help encourage weight gain. When feeding oil in large quantities it is important to further supplement the horses diet with antioxidants to meet the horses increased requirements. Cereal and molasses free with under 1% sugar Rowen Barbary Solution Mash has been specifically formulated for horses that need a higher calorie diet for conditioning and controlled weight gain, whilst being suitable for feeding to horses prone to EMS.
With good management there is no reason why horses with Cushing's cannot live a long and normal life and continue in normal work.