CHALLENGE 7: IDENTIFY AND TREAT CUSHING’S DISEASE

If your old horse doesn’t have Cushing’s disease (technically known as pituitary pars intermedia dysfunction, or PPID), there’s a good chance he’s going to get it. Experts estimate 60 to 70 percent of horses over the age of 20 will develop this endocrine disorder, which begins with the enlargement of the pituitary gland and leads to abnormal production of several hormones, including ACTH (adrenocorticotropic hormone). ACTH in turn stimulates the adrenal glands, located by the kidneys, to increase the production of cortisol, a steroid that produces many of the signs of PPID.

The most visible clue that a horse has Cushing’s is a long, shaggy hair coat that does not shed out normally, but other signs will soon become evident. These include increased drinking and urination, lethargy, abnormal sweating, loss of muscle mass and a diminished immune function that can lead to a propensity for hoof abscesses, skin and respiratory infections, and dental disease. PPID horses are also more susceptible to laminitis.

Sometimes, the effects of PPID are subtle and easily dismissed as “normal aging.” But blood tests can help identify the problem. In one test, a blood sample is taken and the “resting” ACTH concentration is measured.

A second test uses an injection of thyrotropin-releasing hormone to stimulate the endocrine system. In blood samples taken 10 minutes later, levels of ACTH will have risen in all horses, but moreso in those with PPID.

A horse’s ACTH levels can fluctuate with the seasons, which a veterinarian will take into account when interpreting the results.

Cushing’s disease cannot be cured, but the dopamine receptor agonist pergolide (sold as Prascend) can help keep the signs under control. The horse must remain on the drug for life.

It’s also important to keep up with farriery and dental care, as well as parasite control, because horses with PPID are more vulnerable to diseases and infections. Talk to your veterinarian about whether dietary changes may be beneficial. A low-carbohydrate/high-fat diet can help maintain muscle mass while reducing the risk of laminitis. If a horse is not shedding normally, body clipping will help keep him comfortable in warmer weather.

Because PPID can sometimes go undetected, especially in its early stages, testing for ACTH is a good idea as part of routine health checks as your horse ages. “All senior horses should have routine blood work during their annual physicals,” says Ralston.

We can’t protect our horses forever from the passage of time. But we can help them age gracefully, with minimal discomfort. The key is to remain vigilant to subtle changes in their demeanor and condition and to catch developing issues before they grow out of control.

If Folly had the gift of speech, we think he’d say that in horse years, 30 feels like the new 20. In fact, as I have been writing, I’ve watched him spending his afternoon out in his field, throwing the occasional cowkick at his buddies, rolling in the muddiest spot in the field and dozing in the sun. We wouldn’t have it any other way.