A human drug called trilostane offers promise for treating equine Cushing’s disease. This drug works at the level of the adrenal gland to slow down cortisol production. Current research has shown that this drug has reversed some of the symptoms of equine Cushing’s disease.
The pituitary gland dysfunction in equines stems from overgrowth of certain cell types within the gland’s pars intermedia. These cells are hyperactive or present in high numbers, and lead to production of abnormally high levels of many pituitary hormones. While not all of the effects of these hormones are known, some like ACTH are better understood.
Specifically, ACTH over stimulates a horse’s cortisol synthesis by the adrenal glands. The hyper-cortisolemic state leads to the long list of outward problems in the affected animal.
A favorable report from Australia based on a study using trilostane in horses with equine Cushing's Syndrome is favorable regarding clinical improvement, decline in cortisol levels and lack of side effects.
Trilostane caused an improvement in clinical signs in all horses, the most consistent being an improvement in demeanor and a corresponding decrease in cortisol response to TRH administration.
The study concluded that trilostane is a useful therapy for the treatment of equine Cushing's disease, particularly with respect to improving the quality of life of affected animals. Safety and long term effect are currently being studied.
More research is being done to reproduce these findings and prove the trilostane’s safety in horses. Trilostane is available in the United Kingdom, and also to veterinarians in the United States through special arrangement with drug compounding companies.
At this time trilostane is very expensive, but hopefully, as has been the case with pergolide, when demand grows and efficacy and safety are established, this drug will become more available and affordable.
Diet is also gaining significance in the management of Cushing’s disease. Antioxidants, such as vitamins E and C, could play a role in helping to support Cushing’s horses.
Feeding a horse with Cushing's disease can be very challenging, and unfortunately there are no set rules. However, horses with Cushing’s disease do well on the same type of low-sugar, low-starch diet that horses prone to laminitis do.
A good feeding plan usually rules out alfalfa and grain. If the disease symptoms aren’t too severe, then extruded feeds utilizing soy and beet pulp can help keep weight on. Since horses with Cushing's disease are difficult to keep at a healthy weight, balancing diet with exercise is very important.