Abortion in Horses

Question 1

What is the most common cause of abortion in mares in the latter stage of pregnancy? What are the 5 most common etiologies?

Answer 1

placentitis via ascending infections

1. Streptococcus zooepidemicus
2. Escherichia coli
3. Pseudomonas aeruginosa
4. Klebsiella
5. Aspergillus

Question 2

How does placentitis result in abortion in mares?

Answer 2

placental thickening and inflammation and placental detachment at the cervical star region

• uteroplacental insufficiency
• promotion of uterine activity

Question 3

What are 5 important aspects to treatment of placentitis in mares?

Answer 3

1. antimicrobial therapy
2. NSAIDs - Flunixin meglumine
3. Altrenogest (progesterone) - promotes uterine quiescence
4. Clenbuterol - sympathomimetic that suppresses uterine motility
5. Pentoxifylline - decreases inflammatory mediators and increases uterine blood flow

Question 4

What is the most common virus that causes abortion in mares? What are 2 other possibilities?

Answer 4

equine herpesvirus-1

1. equine herpesvirus-4
2. equine viral arteritis virus

Question 5

How can equine herpesvirus-1 abortion be prevented?

Answer 5

vaccination program –> administered 5, 7, and 9 months of pregnancy

Question 6

How does equine herpesvirus-1 cause abortion? What are the 2 ways of transmission to the fetus?

Answer 6

when the fetus is infected during a viremic episode, placental detachment can occur

1. chorionic vasculature
2. inhalation of infected amniotic fluid

Question 7

What are 3 signs of equine herpesvirus-1 infection in equine fetuses? What happens if they survive to term?

Answer 7

1. small necrotic foci on the liver
2. necrotizing bronchiolitis
3. intranuclear inclusion bodies

neonatal herpesvirus infection –> many do not survive more than a few hours/days and demonstrate signs of respiratory distress, icterus, fever, and lethargy

Question 8

How can equine herpesvirus-1 infection be confirmed in the mare and fetus?

Answer 8

• virus neutralization tests
• indirect immunofluorescence
• PCR
• virus isolation

Question 9

How can equine herpesvirus-1 infections be treated?

Answer 9

• theoretically: Acyclovir and Valacyclovir
• best bet is prevention with vaccination protocols

Question 10

What is the most common non-infectious cause of abortion in mares? Why?

Answer 10

twins

diffuse micocotyledonary placentation makes it unlikely that a twin pregnancy will be carried to full term due to limited endometrial surface available for the allantochorion to attach –> fetuses are forced to compete for adequate nutrition and placentation

Question 11

What happens when a mare’s twin pregnancy is maintained to latter stages?

Answer 11

fetal growth becomes more rapid and demanding on the mare until one or both of the fetuses are aborted

Question 12

What happens if a mare carries a twin pregnancy to term?

Answer 12

one or both fetuses will be stunted in growth and size from intrauterine growth retardation

• not uncommon for one or both to have disorders of development

Question 13

When is umbilical torsion seen in mares? What does this result in?

Answer 13

fetus is able to rotate within the amniotic sac and results in excessive twisting of the umbilical cord

constriction of normal flow through the umbilical cord along with edema, hemorrhage, and thrombosis