Abortion in Horses

Most abortions occur from twin pregnancies, when there is not enough space or resources to sustain two fetuses, or a problem with the umbilical cord that can cause damage to the fetus. An abortion can also result from a poisoning, such as a fungus or tent caterpillars on the grass used as a food source. Infectious sources can come from a bacterial, viral or fungal infection. While some mares will exhibit associated symptoms, others may seem perfectly healthy other than the abortion itself. It is important to find the cause of the abortion if spontaneous, so that treatment can be given as needed, and transmission can be prevented to ensure the health and safety of the other horses in the population.

Abortion is when a pregnancy is terminated prematurely. An abortion can occur spontaneously, or it can be medically induced in cases of serious complications, such as twinning, or if the mare’s health is being compromised by the pregnancy.

The main symptoms of abortion is horses are:

• Aborted fetus
• Dead fetus in utero

Associated symptoms can include:

• Premature lactation
• Colic
• Fever
• Purulent vulvar discharge
• Prolonged pregnancy
• Premature separation of the placenta
• Thickened placenta
• Fetal lesions
• Swelling of the limbs
• Decreased appetite
• Nasal discharge
• Swelling of mammary glands
• Depression
• Anorexia
• Diarrhea
• Jaundice in mucous membranes
• Placenta is heavy, edematous, bloody, or covered in brown mucus
• Premature udder development
• Retarded fetus growth

Types

• Spontaneous abortions - Commonly called miscarriages, this is when the fetus is naturally ejected from the uterus
• Medically assisted abortions - These are medically induced abortions that are performed in cases where the fetus is found dead in utero, in a twin pregnancy, or the pregnancy compromises the health of the mare

Causes for an abortion to occur can be divided into non-infectious and infectious conditions.

Non-infectious causes of abortion include:

• Twin pregnancy, or twinning
• Mismating
• Congenital abnormality of fetus
• Mare health compromised due to pregnancy
• To make a mare become a nurse mare
• Umbilical cord abnormalities
• Mare reproductive loss syndrome, due to tent caterpillar ingestion 
• Fescue grass poisoning, due to the fungi Neotyphodium coenophialum 

Infectious causes of abortion are due to a viral, fungal or bacterial infection, and include:

• Equine rhinopneumonitis, caused by the equine herpesvirus 
• Equine viral arteritis  
• Potomac horse fever, due to the Ehrlichia risticii bacteria
• Leptospirosis 
• Bacterial placentitis, due to a Streptococcus species, Salmonella, Klebsiella, Escherichia coli, or Pseudomonas
• Nocardioform placentitis, due to Rhodococcus rubropertinctus, Amycolatopsis spp, Nocardia spp, and Crossiella equi
• Equine mycotic placentitis, including species of Aspergillus spp, Histoplasma capsulatum, Coccidoides spp, Candida spp, Mucor spp, or Cryptococcus neoformans

Diagnosis of an abortion is made if a fetus has been prematurely aborted. Many tests will be performed to determine the cause, so that treatment and prevention can take place to prevent further complications for the mare.

A physical exam, symptoms and medical history may give your veterinarian an idea of what may be wrong. Tests performed on the tissues of the fetus, placenta, or stomach contents or blood of the mare may help to narrow down the cause. Further tests can include fluorescent antibody testing, PCR, virus isolation from fetal tissues, tests on fetal kidney, lung, or liver, and fetal serology testing. The time frame of the abortion and the state of the placenta can also give clues to a correct diagnosis. Be sure to retain the fetus and placenta so that your veterinarian is able to correctly diagnose your mare’s condition.

If an abortion is needed by medical assistance, the mare will be treated with a treatment appropriate to how far along the pregnancy is. The mare may be administered prostaglandin, or iodine, penicillin or saline. Other options for pregnancy termination include transrectal crushing of the embryonic vesicle, allantocentesis, a transabdominal fetal cardiothoracic puncture, a transrectal fetal craniocervical dislocation, placental membrane disruption, or manual membrane extraction. Any of these methods may cause the fetus to be delivered alive, which would necessitate euthanasia.

In cases where the abortion happened spontaneously, the cause is treated if needed. In many cases, such as equine viral arteritis, the mare usually recovers without treatment. In the case of an infection, medications may be given to kill the bacteria, virus or fungus, and measures are taken to isolate any infectious animals from the rest of the population to prevent a spread of the infection. If a mare is at risk of placentitis, she will be examined periodically during the course of the pregnancy by ultrasound for evidence of infection or abnormalities. More often, prevention of any of these conditions is indicated to ensure that the mare does not have any future issues.

After an abortion, your mare needs to be monitored, watching her appetite and demeanor. Symptoms such as vaginal discharge, lack of appetite, depression, or fever may indicate a further problem with the reproductive system, and needs to be reported to your veterinarian.

Prevention is important in managing this reproductive issue. This is done with careful monitoring of mares for any symptoms or problems, isolating pregnant mares from other animals, keeping handling methods hygienic, and using vaccinations. If a twin pregnancy is suspected, have it confirmed before the pregnancy is too far along and causes harm to the mare.

Removing cherry trees, the main food source of tent caterpillars, can prevent mare reproductive loss syndrome. Keep an eye out for other infections on the grass, such as fescue, and be sure to keep mares from eating it if present. Keep infectious mares away from other animals to minimize transmission of the disease. In the case of equine viral arteritis, minimize breeding of infected animals to prevent transmission and carrier stallions.