Equine Cushing's in an Old Mare

Q: I have an older Arabian mare who successfully gave birth to a healthy colt at age 15 before returning to the show ring as a 4-H mount. She was diagnosed with Cushing's disease last year at 18 (she is 19 now). She has very prominent bloodlines and performance ability. Unfortunately, her only living colt had to be euthanized due to severe injuries. We'd like to breed her one last time, but we're unsure of the effect Cushing's will have on a pregnancy. She is otherwise healthy and comes into season regularly. Would it be possible for her to carry to full term with extensive neonatal monitoring?

Katherine, via e-mail

A: Good question. I suspect there are many broodmares that have subclinical Cushing's disease that are untreated and are reproductively normal. I've also observed the other end of the spectrum in mares with uncontrolled Cushing's disease who are experiencing complications of the disease (laminitis, chronic infections, etc.) and deliver compromised foals. In short, in my opinion, it depends on the severity of the Cushing's.

Furthermore, it is important to realize that Cushing's can affect fertility, and it might be more difficult for this mare to conceive. Endocrine testing should be performed on the mare to ensure she is receiving an adequate dose of pergolide to treat the Cushing's. Because pergolide can inhibit mammary gland development, treatment with pergolide should be stopped one month before the anticipated foaling date.

About the Author

Mark T. Donaldson, VMD, Dipl. ACVIM

Mark T. Donaldson, VMD, Dipl. ACVIM, practices with Unionville Equine Associates in Oxford, Pa.

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