Owners often call me out to examine their geriatric horse because they just won't put on any weight or they are walking funny. One disease that must be considered in the older horse is equine cushing's disease. This disease is due to a tumor (adenoma) of the pituitary gland, which is located just under the brain. The adenoma is generally seen in older horses (15 years are older), and the clinical signs of the disease will generally develop over a few years and worsen as the horse gets older if not treated.
Clinical signs typically include the following:
* Hirsutism (a long hair coat): The affected horse usually does not shed out in the spring and summer.
* Laminitis: The degree of laminitis (founder) will vary with each individual. Onset may be either acute or subacute and may become chronic in nature.
* Secondary infections: Frequently, affected horses will develop secondary infections ranging from respiratory infections to delayed wound healing.
* Loss of body condition: Muscle wasting, with thinning of the top line muscles and a pot-bellied appearance.
* Water consumption: Affected horses will drink more water than they have in the past. In addition, they will urinate more and often owners frequently notice wetter stalls.
* Sweating: Affected horses will sweat more than other horses in the same barn or pasture. Part of this is due to the lack of shedding of the hair coat.
* Estrous cycle: Some mare will stop cycling.
Diagnosis is usually made on clinical signs, as there is no specific test to diagnose a pituitary adenoma. However, there are some useful tests that will aid the veterinarian in evaluating the secondary effects of the tumor. The veterinarian will conduct a complete physical examination and rule out other disease and/or conditions that might also cause clinical signs that resemble equine cushing's disease. They include but are not limited to: dental disease, parasitism, liver, kidney and thyroid disease. The most important thing the veterinarian must rule out is malnutrition (more frequent than you might expect as the older horse is "put out to pasture").
Most veterinarians will perform a dexamethasone suppression test, which involves taking a blood sample prior to and 24 hours after administering a shot of dexamethasone. The dexamethasone should depress the cortisol concentration in the horse's blood. If not, then it can be assumed that the pituitary gland is non-functional. In addition, your veterinarian might test the blood or urine for an elevated glucose concentration. While elevated in some horses, this test is often performed in conjunction with other tests.
An important point in treatment of equine cushing's disease is to remember that there is no cure but only management of the disease. Currently, there are two human drugs that are used off label to manage equine cushing's disease. They are cyproheptadine which has antiserotonergic activity and pergolide which is a dopaminergic agonist compound. Both drugs will have to be administered daily and can cost a few dollars a day.
In the warmer months of the year, you will want to clip the hair of your horse to make it more comfortable. You may need to clip your horse every 6-8 weeks in some cases. In the hotter months you will want to run the clipper against the hair to get a closer cut. In the milder months you will want to run the clipper in the same direction as the hair. This will give you a milder cut and keep your horse from getting too cold.
You're going to have to keep a close eye on your horse. Horses with pituitary tumors have a tendency to get secondary infections. Be alert for respiratory infections, laminitis and fevers. Note the long hair coat of cushing's horses will often mask skin infections, make your horse hotter (thus they will breath faster and might look like they have a respiratory infection when they don't), or cause a higher than normal body temperature. Those horses that have laminitis will frequently have subsolar abscesses and require attention from your farrier and/or veterinarian.
The administration of a non-steroidal anti-inflammatory drug to help control the pain associated with laminitis will frequently be prescribed by your veterinarian. Your horse will need to have it hooves trimmed every 6-8 weeks by your farrier to insure a proper hoof axis.
In addition, you will need to closely monitor the diet of your horse. Some horses with equine cushing's disease will maintain their weight, but frequently some will lose body condition. This is why it is important to put your hand on your horse to determine the body condition and not just look at them over the fence (the long hair will make them look fatter than they are).
In summary, equine cushing's diseases is a manageable disease that a many a horse owner has undertaken with success and many equestrians are still enjoying the company of their horses today.
