Abortions in mares occur after rapid separation of the placenta from the endometrium, a layer of the uterus. Of 1211 abortion/stillbirths presented to a diagnostic laboratory in Kentucky, placentitis and dystocia were the commonly diagnosed causes (about 11% each), with congenital abnormalities (8%), twins (6%), umbilical cord torsion and premature placental edema (4% each), and Equine Herpes Virus and bacterial infections (3% each) being the other diagnostic causes (Pugh and Chapman, 1996). Red-bag (i.e., premature placental separations) and stillborn foals frequently are reported by veterinarians and horse owners for mares grazing E+ fescue.

Brendemuehl et al. (1994b) observed the effects of E+ fescue on mare cyclicity, pregnancy rates, and embryonic death rates. Mares grazing E+ pastures had prolonged luteal functions, decreased per cycle pregnancy rates, and increased early embryonic death rates, when compared with those grazing E- pastures.


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