Occasionally a mare will expel a fetus before it has reached full term. This is commonly called of the fetus. Technically abortion describes the termination of pregnancy after organogenesis, but before the fetus can survive without maternal support. Early embryonic death is a term that describes the termination of gestation before is complete, and describes the expulsion of a dead, full term fetus.
Non-Infectious Causes of Abortion
Twining
Abortion due to twining is caused by a placental to support two full term fetuses. Abortion due to twining usually occurs at six to eight months gestation and may be preceded by premature lactation. In most cases both fetuses are expelled at or close to the same time. To prevent abortion due to twining, most veterinarians will artificially terminate or transfer the less developed embryo early in gestation to allow the other embryo to develop to term. Only 1% of twin births are successful.
Umbilical Torsion
Torsion, or twisting, of the umbilical cord during gestation cuts off the fetal supply resulting in the ischemic necrosis of the fetus. Excessive length of the umbilical cord can predispose for excessive twisting of the cord. The necrotic fetus is subsequently expelled from the uterus. Abortion due to umbilical torsion may occur after organogenesis has occurred. Before this time early embryonic death occurs and the embryo will most likely be phagocytized in the uterus. Umbilical torsion is seen as haemorrhage from the umbilicus and the swelling of the fetal tissue associated with hypoxic necrosis of tissues.
Ectopic Pregnancy
Ectopic pregnancy occurs when an embryo encysts of the uterus. The most common site for ectopic pregnancy is in the wall of the abdomen though the embryo may migrate to the pelvic cavity or the hind limb. Ectopic pregnancy is detectable through ultrasound revealing the absence of the fetus within the uterus and the presence of a fetus outside the uterus. This is usually detectable before seven months gestation. The mare will produce all the hormones associated with pregnancy and exhibit the traits of true pregnancy making serology or clinical presentation useless in diagnosis. Ectopic embryos may be surgically into the uterus to finish normal gestation if detection is prompt.
377
Made with FlippingBook Publishing Software