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.
To see if a single dose of dexamethasone would interfere with ovulation, Bucca and colleague Andrea Carli, DVM, evaluated the effects of dexamethasone administered at the time of breeding on ovulation rates.
"The purpose of our study was to determine if a standard dose of hCG was able to induce ovulation in mares that had been treated with a single dose, rather than multiple doses, of dexamethasone (to prevent endometritis) at the time of breeding," explained Bucca.
Bucca and her colleagues analyzed medical records from 152 mares over 223 estrous cycles at an Irish stud farm. In 113 cycles, they administered both 50 mg of dexamethasone and 1,500 IU (international units) of hCG to induce ovulation. In the remaining 110 cycles they administered only the hCG. All mares were subsequently bred.
"We found that a single dose of dexamethasone at the time of breeding did not interfere with ovulation," concluded Bucca. "Deaxamethasone and hCG have a role in the breeding management protocols of mares known to be susceptible to persistent mating induced endometritis. The two drugs can be safely administered without interfering with ovulation rates."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.