Complications of the Late Pregnant Mare

Introduction

Late pregnant mares are affected by a variety of conditions including infectious agents, or missed twins. Less commonly, mares will suffer from functional or structural defects such as placental abnormalities, ruptured prepubic tendon, hydropic conditions or abdominal hernias. The following is a review of conditions that a practitioner might encounter when working with pregnant mares, and approaches for management.

Bacterial placentitis/Abortion

Pregnancy losses through placental infection account for approximately 30% of equine abortions within the United States. Bacteria are the most common cause of placentitis with Streptococcus equi subspecies zooepidemicus, Escherichia coli, Klebsiella spp, Pseudomonas spp, and Staphylococcus aureus most often implicated in disease. Infection generally begins via the caudal reproductive tract. Mares are usually affected during the last trimester of pregnancy. Infective organisms invade and disrupt the intimate contact between the allantochorion and endometrium. Placental compromise generally results in premature delivery of a nonviable foal.

The most common clinical signs of placentitis include premature udder development and purulent vulvar discharge. It should be noted that severity of clinical signs does not necessarily determine the outcome of the pregnancy. Some mares will have scant to no vulvar discharge present and/or minimal udder development. These pregnancies may suffer a subclinical infection and result in death of the fetus. Alternatively, some mares have copious vulvar discharge and extensive placental separation but will deliver viable foals. [...]