A new study published in the peer-reviewed journal Theriogenology reveals more about nocardioform placentitis, a placental infection that has plagued breeders and stud farm managers for decades. Placentitis is believed to account for 19 percent of equine infectious abortions nationwide, but much remains unknown about the disease.
A research team led by Dr. Carleigh Fedorka at the Gluck Equine Research Center in Lexington, Ky., studied 264 mares — 145 who were suspected to have the disease and 119 with apparently healthy pregnancies — and compared characteristics of their pregnancies and resulting foals.
The study found that nocardioform placentitis tends to be associated with older mares, and it isn't contagious between mares in the same turnout group. One episode of nocardioform placentitis does not necessarily presuppose another in the same horse the following year, and mares did not seem to experience abnormal cycles or reduced fertility after a case of nocardioform placentitis. Mares who were given antibiotics and hormones throughout their pregnancies to stave off the disease were no less likely to develop a case of nocardioform placentitis than those who were not.
While one of the most classic symptoms of nocardioform placentitis is abortion, some mares whose placenta indicated they had the illness did produce live foals. The study found those foals were smaller than average, but were otherwise healthy and had normal blood counts at birth.
Interestingly, the size of the placentitis lesion on an infected mare's placenta seemed to vary according to the date of breeding, with mares bred later in spring showing larger lesions.
Nocardioform placentitis is believed to be caused by bacteria, but researchers don't know how the bacteria causes the inflammation of the placenta that's characteristic of the disease. It's characterized by premature mammary gland development, thickened placental and uterine walls on ultrasound, or visible separation of the placenta from the uterine walls on ultrasound. There are several forms of placentitis, but the nocardioform version is accompanied by a thick, brown mucous covering the placenta at the site of the lesion, which prevents the placenta from continuing to support the fetus in some cases. Nocardioform placentitis case numbers seem to sometimes wax and wane across breeding seasons, suggesting that season or weather conditions may play a role in its development.
Read the full study here.
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