Cushing’s and Equine Metabolic Syndrome

Some people think that there is more Equine Cushing’s around than there used to be but the reality is that more horses are being tested and treated for it than in previous years, hence the seemingly increased and increasing incidence.

What is Cushing’s disease?

Equine Cushing’s also known as PPID which stands for Pituitary Pars Intermedia Dysfunction, is an hormonal illness that affects horses and ponies and also other species such as dogs. PPID is caused by a progressive nerve degeneration in part of the brain called the hypothalamus and this results in a decrease in the secretion of a substance called dopamine. Dopamine is important in the control of the pituitary gland, specifically the part called the pars intermedia, hence the name of the disease. The pars intermedia controls the production of two hormones called ACTH and cortisol.

Cushing’s disease results in a weakened immune system so horses are more prone to infections and wounds can take longer to heal, it also had other symptoms. It tends to be associated with old horses but in fact horses in their teens can test positive for Cushing’s, and some even younger than that. Cushing’s comes with a bucket load of symptoms or sometimes, none at all. In 2016, it was the most frequently reported equine illness but that is partly down to an increased awareness from owners and proactive marketing by pharmaceutical companies who will often offer a free blood test. Common symptoms may include:-

• Increased thirst and urination
• Abnormal coat changes so unexpected growth at odd times of year, sometimes this may include a long or curly coat but these signs tend to be associated with horses who have had the disease for some time
• Recurrent infections, particularly in the hoof and the skin
• Lethargy and depression
• Muscle wastage, typically a pot bellied appearance and lack of top line
• Laminitis
• Excessive or patchy sweating

How do you determine if your horse has Cushing’s disease?

A simple blood test which needs to be sent away to the lab will confirm the diagnosis. The lab has a reading or level, a different one for every day each month and the results will be presented to you as a numeric level as against the lab level. If your horse’s level is higher than the lab level, then they have tested positive for Cushing’s.

The lab levels vary from day to day and month to month. The most sensitive time to test the horse is in September and October when the reducing daylight hours begin to affect the pituitary gland. So throughout the course of a year, your horse will have different readings and they will fluctuate, the key thing is comparing them to the lab level in place at that point in time.

Sometimes, the blood test fee will be free, usually for a first timer, subsequent tests for a horse that has been tested before, will normally incur a charge. Your vet will also charge for the visit and for taking the blood from the horse. Results are very quick, usually back within a day or two.

Some horses clearly exhibit symptoms of Cushing’s disease whereas other do not. Some horses show classic signs of the illness but test negative; Equine Cushing’s is not an inevitability of old age. The main thing is you can’t always tell by looking, so a blood test will confirm the position.

Owner’s comment

“My mare was tested for Cushing’s from age 20, she wasn’t showing any signs but she has a host of other problems and I didn’t want to get caught out, particularly with laminitis. Her levels were fine, on or around the threshold until she was 23 when she really started to struggle. She had a tooth removed and there was infection present so I opted to medicate her at that point to help her immune response. She started on 1 tablet and that was two years ago, she has just gone up to 2 tablets per day. I have regular blood tests to keep an eye on her levels but happily, she has never really shown any symptoms apart from odd infections and perhaps a longer coat earlier in the season. She eats the tablet really easily, I put it in something crunchy like a carrot scored down the middle or wedge it into the centre of a sugar free Polo.”

What is the treatment for Cushing’s?

Treatment is by tablet with a drug called Prascend and the vet will recommend the appropriate dosage. The tablet is scored in the middle and can be snapped in half quite easily. Ongoing blood tests are required to monitor the levels as they will rise and the dosage of Prascend may need to be increased in line with this.

Because of the increased risk of laminitis associated with Cushing’s disease, it is recommended that affected horses are fed as a potential laminitic risk, so a diet with a naturally occurring sugar level of no more than ten percent. There are lots of feed companies who offer appropriate feeds particularly for veteran horses which fall into this category.

Can affected horses still be ridden?

Many horses continue to work, sometimes at a very high level, with the appropriate medication and management. Some horses, if they are elderly, may have other issues which force retirement rather than Cushing’s disease. Each horse needs to be viewed holistically and treated as an individual case.

Is Equine Cushing’s Disease the same as Equine Metabolic Syndrome?

The two diseases are easily and often confused but Equine Metabolic Syndrome or EMS is actually insulin resistance although it shares some common symptoms with Cushing’s disease including laminitis. EMS actually causes increased metabolic efficiency in the horse and can result in obesity; it tends to affect younger and middle aged horses whereas Cushing’s disease is associated with horse in their late teens and older although, as with all conditions, there are some horses that buck the trend in terms of the age range.

Research into Cushing’s Disease

As more horses and ponies are tested, large quantities of data are becoming available to scientists about this illness. Already in recent years, labs are producing daily results levels whereas only two or three years ago, the data was not sufficiently sensitive or developed and the lab readings only altered on a monthly basis. Every time your vet sends in a blood sample to test for Cushing’s disease, they have to give the horse’s age, height and breed so it is hoped that all this data will eventually be able to produce useful conclusions going forward for horse owners. Already the increased awareness of the disease and the use of Prascend combined with non steroidal anti-inflammatory drugs such as Danilon, mean that many horses are living to much greater ages with excellent quality of life.