Dexamethasone Use in Pregnant Mares

Q. Can you help me locate information on steroids given to a mare during pregnancy? The mare has been receiving dexamethasone for cancer up until two months before her due date. The cancer then returned. I would like to help research further treatments.

Katie Fennimore

A. It is not clear why the mare is on dexamethasone, so I am assuming she has lymphosarcoma. In som cases, lymphosarcoma gets worse during pregnancy because there are changes in the mare's immune system. During pregnancy, the mare mounts a different type of immune response that may allow the cancer or other chronic diseases to worsen. I do not know the dose of dexamethasone the mare is on, but I recommend that she be placed back on the drug if she has cancer. The dexamethasone will not harm the fetus as long as the daily doses are less than 100 mg/day. Unlike in the cow, dexamethasone does not cross the equine placenta. As we don't know what type of cancer the mare has, other treatments cannot be recommended.

About the Author

Michelle LeBlanc, DVM, Dipl. ACT

Michelle LeBlanc, DVM, Dipl. ACT, is a theriogenologist (reproduction specialist) for Rood and Riddle Equine Hospital in Lexington, Ky. She was previously a professor in equine reproduction at the University of Florida. Her interests deal with mare infertility, embryo transfer, placental infections in mares, and acupuncture in infertile mares. She owns Thoroughbred/warmblood crosses and she competes in dressage.

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