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Cushings Disease in Horses


Last September I was called out to examine an 18 y.o hunter cob which was reported to be very lethargic, sweating a lot after exercise and had held onto its summer coat. The cob was due to be prepared for the hunting season. The owner was very concerned and also reported that the animal had a recent episode of laminitis.

On arrival I noticed that the cob had lost muscle mass since I had seen him 3 months previously. He had a potbelly and his coat was thick and long and I could see that he had been sweating a lot after recent exercise. The owner told me that she had noticed him drinking a lot of water and urinating a lot more than the other horses.

At this point I had seen enough to give the owner a provisional diagnosis of Equine Cushings Disease, with the possibility of there also being insulin resistance at the same time.

This both alarmed and confused the owner. Her first question to me was if I could save her horse.

To put her mind at ease I suggested that I would firstly explain the cause and symptoms of Cushings Disease to her. Then I would explain how I intended to diagnose if her horse had the problem and, if so, how I could treat it.

Cushings Disease is a condition usually associated with older horses and ponies (over 15 years).
It is caused by a tumour of the pituitary gland, which lies at the base of the brain. The tumour distorts the gland and results in alterations to the normal levels of hormones being produced there. This results in a knock on change in these hormone levels in the body, which can have adverse effects. One such hormone, ACTH acts on the adrenal glands (which lie near the kidneys), stimulating them to produce cortisone. The elevated levels of ACTH in Cushings Disease lead to high levels of cortisone in the blood and this can have a detrimental effect on the horses’ body and on its health.

There are many symptoms of Cushings Disease, all of which do not occur in each case.
They include:
Sudden excessive thirst and urination, long, thick curly hair that does not shed in summer, pot belly, loss of muscle on the top line, depressed lethargic look and filling above the eyes instead of the normal depression seen there.
High levels of cortisone in the blood can result in conditions like respiratory problems, skin problems, foot abscesses, dental disease, chronic laminitis and a compromised immune system

This cob was demonstrating many of these signs, hence my suspicions.

At the risk of adding confusion, I also explained that there was a similar condition called insulin resistance, which I would also check for. It has similar symptoms and can occur on its own or at the same time as Cushings Disease. The similar symptoms include recurring laminitis and abnormal weight distribution.

Blood tests for ACTH hormone, insulin and glucose are used to diagnose Cushings Disease and insulin resistance.

When the results came back they indicated that the cob indeed did have Cushings Disease and did not have insulin resistance.
I explained that the condition was treatable with an oral medication. This would have to be given to the cob for the rest of his life. While there is no way of surgically dealing with a pituitary tumour, we would hope to get many years of effective treatment on medication. However the tumour may cause more problems in years to come. When a diagnosis is achieved early on, like this case, the treatment can be very successful and the horse can return to normal health.

I recommended immediate treatment with a prescription medication and explained that I would have to do follow up blood tests to monitor the ACTH levels to achieve the optimum level of medication

The owner asked me what would be the case if the cob had showed positive for insulin resistance as well.

I explained that the approach there would have involved restricting the animals’ diet, especially its intake of carbohydrates and careful monitoring of mineral levels. Thankfully we did not also have to worry about this in this case.

I explained to the owner that there were certain things that she could do to help the cob deal with Cushings Disease. These included avoiding stress, mainly by adhering to a familiar routine, attention to hoof and dental care and a regular de-worming and vaccination programme.

Since treatment has commenced the cob has made steady progress and is now back in regular work. With careful management I feel he will have a normal life for many years to come.