There are upsides and downsides to administering dexamethasone, just as there are with most drugs. For instance, dexamethasone is a potent anti-inflammatory but can cause life-threatening laminitis in some cases. And while dexamethasone can be used successfully to treat mating-induced inflammation of the uterus (endometritis), some veterinarians believe it prevents ovulation and, thus pregnancy.

"All mares develop a mating-induced endometritis when semen is deposited into the uterus, regardless of whether it is natural breeding or artificial insemination," explained Stefania Bucca, DVM, of the Irish Equine Center in Johnstown, County Kildare, at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas. "About 15% of mares develop an ‘overwhelming’ reaction that is referred to as a persistent mating-induced endometritis, that will negatively influence embryo development and survival."

According to Bucca, researchers on a previous study found that a single 50-mg dose of dexamethasone administered at breeding time to mares susceptible to persistent mating-induced endometritis prevented full-blown inflammatory reactions and improved conception rates significantly when used in combination with human chorionic gonadotropin (hCG).

"A subsequent experimental study, however, found that administration of 25 mg dexamethasone twice daily for five days resulted in a high proportion of ovulation failures," said Bucca