by Tori Jordan BA VetMB MRCVS
Does your horse or pony suffer from recurrent episodes of laminitis? Does he seem to contract laminitis at an unusual time of year, with no obvious predisposing factor? If so, it may be worth considering having your horse tested for Cushing’s disease. This month’s article focuses on the facts you need to know about this extremely common condition.
What is Cushing’s disease?
Cushing’s disease is a hormonal condition in which the adrenal gland produces too much of the steroid hormone, cortisol. The condition is also known as Pituitary Pars Intermedia Dysfunction (PPID), which reflects the most common cause – excessive replication of the cells of the pituitary gland. This leads to increased release of ACTH, the product that signals to the adrenal gland to say that the body needs more cortisol.
What are the symptoms of Cushing’s disease (PPID)?
It is generally accepted that PPID is a condition of older horses and ponies and indeed it has been thought of by some as part of the normal ageing process. However, with recent advances in testing, PPID is becoming increasingly diagnosed in horses and ponies in their teens. PPID is more common in pony breeds but can occur in any type or breed of horse or pony.
Many people are aware of the classical picture of a Cushingoid pony – a long, curly haired coat that is unlikely to be confused with any other condition. Yet, this characteristic coat is often late to develop in the disease course. Symptoms that may be seen before this point include delayed shedding of the winter coat, lethargy, abnormal fat deposits (e.g. behind the shoulder and over the hind quarters), excessive sweating, increased thirst, increased urine output, muscle wastage and bulging of the hollows normally seen above the eye.
The most important clinical sign, however, is a predisposition for laminitis. Up to 90% of cases of laminitis can be attributed to a hormonal cause, whether that be PPID or equine metabolic syndrome. The method by which PPID and laminitis are linked is unclear, though many theories have been suggested. Some blame the increased levels of cortisol for the changes that occur within the foot, while others believe they occur due to insulin resistance, which also occurs with the condition.
How can I tell if my horse is suffering from the condition?
If you are suspicious that your horse or pony may have PPID, it is best to contact your vet for advice on the tests they recommend. While clinical signs can be suggestive, they are often not enough to provide a definitive diagnosis.
The most common and by far the simplest way of testing for PPID involves a single blood test. The test measures levels of ACTH, the hormone described at the beginning of this article. Horses and ponies with PPID have higher levels of this hormone than those who are free from the condition.
Can Cushing’s disease be treated?
There is no cure for PPID. However, the condition can be controlled using a combination of medical therapy and general management practices.
Pergolide is the only drug licensed to treat the symptoms of PPID. This drug is a dopamine agonist, which means that it simulates the action of dopamine in the body. Dopamine, and hence, pergolide, acts to inhibit the pituitary gland, preventing it from releasing excessive amounts of ACTH. Pergolide comes in tablet form and can be hidden in feed or dissolved in water and injected straight into the mouth with a syringe, just like a wormer. It can take some time to find the dose that suits your horse or pony best and so your vet may request a repeat blood sample 4-6 weeks after the start of treatment in order to check that the drug is doing its job. It is worth noting that it can take 6-12 weeks before you notice an improvement in your horse or pony but the drug has been found to be effective in as many as 80% of cases.
As well as medical therapy, your horse may benefit from several straightforward management practices aimed at controlling clinical signs of PPID. The overproduction of cortisol that occurs with the condition can lead to suppression of the immune system, which can result in increased susceptibility to infections. Hence, it is advisable to keep your horse up to date with his vaccinations and worming treatments (including regular faecal egg counts), and to tackle any illnesses or infections as soon as they are noticed. Regular dental care can also be of great help, both by reducing the likelihood of infections in the mouth and by optimising digestion. Routine visits by the farrier and management of your horse’s diet are hugely important in minimising the risk of laminitis, while a long, curly coat can be controlled by regular clipping. Each of these changes, though simple in themselves, can make a big difference to your horse’s quality of life. In an attempt to identify laminitis-prone horses and ponies early, the drug company Boehringer Ingelheim are currently running a promotion on diagnostic testing for PPID. Until 30th November 2012, lab fees for the ACTH test will be free, provided that the sample is posted accompanied by a voucher obtainable by you or your vet from www.talkaboutlaminitis.co.uk. Postage fees will be charged as normal.If you have any questions about any aspects of your horses’s health, or indeed your pet, farm or smallholding animals, please do not hesitate to contact us on 01892 835456. Putlands Veterinary Surgery is based in Paddock Wood in Kent, and offers a friendly, proffessional and personal service for all species of animal. We have four dedicated large animal vets with a wealth of equine experience between us, and are always happy to help.