Environmental Factor in Cushing's?

Q. I have been treating an aging pony mare for Cushing's syndrome. She had been chronically foundering for three years when she abruptly started exhibiting diabetic symptoms. After reading your article on Cushing's and conferring with my veterinarian, we put her on pergolide. Her diabetic symptoms disappeared, and she is now back to normal.

My other mare, a 19- or 20-year-old Thoroughbred, now is getting the wavy hair coat associated with Cushing's. My first horse, a gelding, lived to the ripe old age of 34 in the same environment. He did have the fatty tumors often associated with older horses, but not Cushing's.

My question is--could something in the environment be predisposing them to the syndrome?


A. First of all, I congratulate you on caring for your first horse until age 34! Over the past couple of decades we have seen more and more clients like yourself who want to keep their aging equine friends as companions rather than having them put to sleep simply because they have passed the age of 25. Further, it is clients like you that have pushed veterinarians like me to increase our understanding of equine geriatric medicine.

Although we have learned a lot about equine Cushing's disease, there is certainly more to learn. Your question about environmental factors that might predispose horses to Cushing's disease is an interesting one. At present, we are unaware of potential environmental risk factors that predispose people, dogs, or horses to Cushing's disease. However, I should also mention that little research has been performed to address this question (largely because such studies would require decades to complete).

Currently, we do recognize that some breeds (Morgans especially) and types of equids (ponies in particular) are at greater risk of developing Cushing's disease. These observations, accompanied by the fact that Cushing's disease has been recognized for a number of decades in horses, suggest that genetics likely plays a more important role than environment in development of Cushing's disease. Clearly, your three equids are not related so in their case it might simply be that you care for them into old age.

About the Author

Harold Schott II, DVM, PhD, Dipl. ACVIM

Harold Schott II, DVM, PhD, Dipl. ACVIM, is a professor of equine medicine at Michigan State University.

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