Diagnosis, Management, and Diagnostic Investigation of Abortion

Careful management of pregnant mares and preparation for parturition is essential to help prevent cases of equine abortion--losses of pregnancy between 150-300 days of gestation. "The incidence of abortion in mares ranges from 5-15%, and this has a severe economic impact on the equine industry," said Karen Wolfsdorf, DVM, Dipl. ACT, a veterinarian with Hagyard Equine Medical Institute in Lexington, Ky., in a presentation at the 2006 Hagyard Bluegrass Equine Symposium held October 18-21 in Lexington. This impact is not only due to foal loss, but the mare is rendered unproductive for that year, and she has a decreased fertility rate for the next year. This means there is a potential two-year loss in the mare's production for her owners.

According to Wolfsdorf, although noninfectious causes of abortion are diagnosed twice as frequently as infectious, when an abortion occurs, it is very important that the farm implements isolation protocols immediately. She cautioned several times that it is "better to be safe than sorry."

When an abortion has occurred on a farm, the first thing Wolfsdof is interested in is the mare's history--how far along was the mare in her pregnancy? What horses has the mare been in contact with? Is the mare sick? Are a fetus and placenta present? Next, Wolfsdorf performs a physical and reproductive examination. She takes the mare's temperature, pulse, and respiration, checks her mucous membranes, and evaluates her gastrointestinal motility/feces. Wolfsdorf examines the vulva for tears and bruising, and she inspects the expelled placenta and fetus (if present) to make sure they are intact and to note any gross abnormalities. Finally, she performs a rectal palpation and ultrasound if the fetus or placenta are not present or a vaginal/uterine examination to make sure nothing is amiss inside the mare as a result of the abortion and/or the fetus or the part of the placenta are not retained.

The management of the mare and the environment is essential. Wolfsdorf says to separate the affected mare from other mares in the field to decrease the chances of potential exposure to infectious agents. If the mare aborted in a field, and the field is contaminated, rope off that section of the field. Wolfsdorf cautions not to "remove the exposed mares or mix them with others on the farm until tests for equine herpesvirus, leptospirosis, and equine viral arteritis (EVA) are returned as negative. If the mare aborted in a stall, remove everything in the stall, place her in a pasture by herself, and disinfect the stall.

The laboratory component of an equine abortion is also very important, according to Fairfield Bain, DVM, MBA, Dipl. ACVIM, ACVP, ACVECC, a veterinarian at Woodside Equine Clinic in Ashland, Va. According to Bain, the clinical evaluation of the animal, premises, and history are vitally important to the diagnostic process. Diagnostic laboratory evaluation includes microbiology (dealing with microscopic forms of life), serology (having to do with serums--especially their reactions and properties), and histopathology (pertaining to tissue changes characteristic of disease). In some cases, molecular diagnostics might apply.

It is important to submit the complete placenta and fetus for diagnostic examination if possible. Bain says, "It is helpful to lay the placenta out in an F-shape arrangement with the horns of the chorioallantois (a vascular fetal membrane) or the red velvety side pointing outward from the body and have the umbilical cord and amnion (a thin membrane forming a closed sac around the embryos or fetuses) extending through the opening at the cervical star (a small area on the placenta that was adjacent to the cervix during gestation)."

Placentitis (inflammation of the placenta) is the leading cause of abortion, and it is usually infectious, according to Wolfsdorf. Noninfectious causes of abortion include dystocia-perinatal asphyxia (a difficult birth that results in a lack of oxygen or excess of carbon dioxide that leads to unconsciousness and often death of the foal), congenital anomalies, twinning, improper placental separation, placental edema (swelling), and other placental disorders, torsion of the umbilical cord, bacteremia (presence of bacteria in the blood), and fetal diarrhea.

With increased awareness and education, Wolfsdorf feels that veterinarians should be able to produce more positive results from noninfectious causes such as twinning, umbilical torsion/pole ischemia (wrenching of the umbilical cord/deficient supply of blood to the extremity), and intrapartum/perinatal asphyxia (oxygen deprivation during delivery or shortly after birth). According to Wolfsdorf, the use of ultrasonography of the reproductive tract at an early stage of gestation (11-15 days) has led to a decrease in the incidence of twin abortions. Also, most perinatal asphyxia cases are associated with oversized fetuses, fetal malpresentation during birth, maiden mares, and foals that aren't attended when they are born. Wolfsdorf believes that watching mares that are about to foal more closely, and having the necessary support on hand to correct dystocias and resuscitate foals can decrease the incidence of these losses.

Abortions caused by infectious agents occur less frequently, but these cases can be even more devastating for all involved. Fortunately, according to Wolfsdorf, improved methods of preemptive monitoring, vaccinating, testing, isolating, and treating are available to combat these diseases. Bacterial placentitis is most commonly caused by Streptococcus spp., which can be identified from the placenta and the aborted fetus, according to Wolfsdorf. Bacterial Leptospira spp. (spirochetes that cause devastating infections in humans, horses, and other animals), nocardioform actinomycete (bacteria consisting of gram positive filamentous aerobic organisms), and Aspergillus spp. (the most common fungus isolated in abortion cases) are frequently associated with placentitis. Equine herpesvirus and EVA should also be considered important potential pathogens in abortions, especially when multiple incidences occur. Vaccination against herpesvirus has decreased the incidence of abortion "storms" drastically, said Wolsdorf.

Abortion can be devastating for horse owners, managers, and veterinarians.  However, increased knowledge and implementing proper protocols can greatly reduce the risk of multiple abortion cases. Horse owners and veterinarians need to be prepared for an abortion and know how to work together to handle such matters on the farm.

About the Author

Rachael C. Turner

Rachael Turner is the former Photo and Newsletter Editor for The Horse. She is an avid event rider. Rachael's main focus is dressage and on training young horses with the proper foundation for success. She is also a member of the United States Dressage Federation and the United States Equestrian Federation. Her website is avonleaequestrian.com.

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