Equine Twinning Study Guide

Overview and Clinical Importance

Twin pregnancy in the mare is one of the most significant causes of reproductive loss in equine practice, historically accounting for 20-40% of all equine abortions. The equine uterus is uniquely designed to support only a single fetus, making twinning a high-stakes clinical scenario that demands early diagnosis and intervention. With the advent of transrectal ultrasonography, the incidence of twin-related abortions has decreased to approximately 3% due to early detection and management.

The consequences of unmanaged twin pregnancy include: mid-gestation abortion (5-9 months), stillbirth, delivery of weak dysmature foals, increased risk of dystocia, retained placenta, and compromised future fertility of the mare. Fewer than 10% of twin pregnancies result in two live healthy foals, making early intervention essential.

Etiology and Pathophysiology

Types of Twin Pregnancy

Dizygotic twins (non-identical) account for the vast majority (greater than 95%) of equine twin pregnancies. These result from fertilization of two separate oocytes from multiple ovulations, either synchronous (within 24-48 hours) or asynchronous (greater than 48 hours apart). Viable stallion sperm can survive in the mare's reproductive tract for several days, allowing fertilization of oocytes from asynchronous ovulations.