Losing a foal any time during gestation is heartbreaking for breeders, but even more so when it happens near term. What can owners and veterinarians do to prevent late-term abortion, especially those that result from infections in the placenta?
"Minimizing late-term abortion can be achieved by early recognition of an infection and inflammation of the placenta and aggressive medical treatment," said Peter R. Morresey, BVSc, MACVSc, Dipl. ACVIM, ACT, an associate at Rood & Riddle Equine Hospital, in Lexington, Ky., during his presentation at the 12th Congress of The World Equine Veterinary Association, held Nov. 2-6, 2011, in Hyderabad, India.
According to Morresey, veteran mares that have foaled before are at a higher risk of developing a placental infection because they often have one or more anatomic defects in their reproductive tracts from previous foalings (involving the external genitalia) that allow opportunistic bacteria to be transferred from the vagina to the uterus through an incompetent cervix.
"Once the placenta becomes infected with bacteria, the fetal membranes become thick, which impedes the transfer of nutrients and gas exchange between the mare and foal," explained Morresey. "In addition, thickening of the placenta at the 'cervical star' (where the foal normally erupts through the placental membranes) can prevent rupture during delivery and compromise the health of the fetus, and bacteria can build up in this area and cause an infection in the neonatal foal."
Serial monitoring of at-risk mares (i.e., those with anatomic abnormalities of the vagina and cervix that predispose them to infection) and early detection of placentitis--such as precocious mammary development and vulvar discharge--is essential beginning around the seventh month of gestation. Some common tests include:
- Transrectal ultrasonography to measure the thickness of the uterus and placenta and to visualize the cervical star;
- Transabdominal ultrasonography to assess the foal's heart rate, activity, and size; and
- Measuring hormone levels such as progestin concentrations that can indicate placental abnormalities at certain stages of gestation.
If a veterinarian identifies infection and placentitis, treatment is essential. The inflammation initiates an inflammatory cascade that can--and often does--lead to premature fetal expulsion and neonatal death.
"Anti-inflammatory drugs to decrease inflammation and antimicrobials to fight the infection are both rational choices as well as progesterone to 'quiet' the uterus," Morresey advised. "Together with early detection, these drugs will help manage affected mares to successfully maintain pregnancy until term."
A full summary of Morresey's presentation, which was co-authored by Michelle LeBlanc, DVM, Dipl. ACT, also from Rood & Riddle, will be available for free on the International Veterinary Information System.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.