Equine Cushing's Disease

We receive a large number of calls regarding Equine Cushing’s Disease into the helpline all year round, however during this time of the year there is often an increase in diagnoses due to seasonal fluctuations in ACTH levels, but how and why are these two conditions linked? 

Pituitary Pars Intermedia Dysfunction (PPID) or Equine Cushing’s Disease is an increasingly common hormonal disorder normally seen in more elderly horses and ponies. It is a disorder associated with the malfunction of the pituitary gland, which sits at the base of the brain. The pituitary gland plays a vital role in regulating hormones within the body, however in horses with PPID, levels of dopamine are significantly reduced. Dopamine acts to lower the amount of Adrenocorticotropic Hormone (ATCH) being secreted from the pituitary gland, so when levels are decreased the ACTH level in the blood rises.
As shown in the graph below seasonal variations in the level of ATCH are apparent in all horses, with a peak in August to October. This is due to a number of biological and environmental factors which your vet will take into account when testing for PPID, however horses with PPID will have elevated ATCH all year round.

So how is this linked with laminitis? Well this elevated ATCH level will increase the production and release of cortisol from the adrenal glands, which in turn increases circulating blood glucose. Leading on this will affect insulin production and can lead to insulin resistance, a major risk factor for laminitis.
These hormonal changes also have a substantial impact elsewhere in your horse’s body and can lead to a variety of different symptoms. These can include unusual hair growth (the classic curly coat), loss of topline, excessive drinking and urinating, lethargy, a pot-bellied appearance and abnormal fat deposits especially above the eye. A horse with PPID may exhibit a number of these symptoms, just one or none at all so if you are at all concerned chat with your vet.

If you do suspect your horse or pony to be suffering from one or more of these symptoms a free lab test is currently being offered until the end of October through the national “Talk About Laminitis” initiative. By filling in your horse’s details on the www.talkaboutlaminitis.com web page you will be entitled to a free basal ACTH test carried out by your vet. This will measure the daily baseline level of ACTH hormone in your horse’s blood and will identify if their baseline is higher than would be expected.

If your horse is identified as a cushingoid then you will need to consider if your current management practices (e.g. turnout and feed) are suitable and make any changes necessary. It is recommended to avoid feeds high in starch and sugar, instead providing calories from oil and fibre to aid in maintaining a stable blood glucose level and reduce the risk of a laminitic attack occurring. If your horse is a ‘good doer’ then a high quality balancer providing antioxidant support or a high fibre based feed are ideal.

Another important consideration is maintaining your horse’s electrolyte balance. Due to the unusual hair growth that can occur your horse may maintain a thicker than normal coat throughout the year leading to them sweating more than usual. If your horse is also urinating more frequently we have a double whammy as essential electrolytes are released from the body in sweat and urine, it is therefore important to ensure your horse’s diet has sufficient electrolyte levels to top up what is lost. For a light sweat a tablespoon of salt daily will be sufficient, however if the horse is heavily sweating an electrolyte supplement will be required.

For this and more advice on dietary considerations for your cushingoid there is an Equine Cushing’s factsheet available on the Dodson & Horrell website (http://dodsonandhorrell.com/factsheet-library). Furthermore we are available for advice on this and many other feeding and nutritional topics on the Helpline. We can be contacted through the enquiry page on the website or by telephone on 0845 345 2627.