Late-term pregnancy loss compromises mare welfare, reduces production, and results in emotional and financial losses in various sectors of the equine industry. Veterinarians know that equid herpesvirus-1 (EHV-1) infection in pregnant mares can cause abortion and neonatal foal death, but risk factors for EHV-1-associated abortion have long remained unclear. Researchers recently took a closer look at risk factors and have made some important discoveries.

Julia Kydd, PhD, a lecturer in applied immunology and senior tutor in the Faculty of Medicine & Health Sciences at the University of Nottingham, in the United Kingdom, and colleagues have found that the genetic makeup of the mare or her placenta (half of which is inherited from the father) appears to play an important role in abortion caused by EHV-1. Specifically, Kydd said, certain genes in the mare’s DNA belonging to a region called the major histocompatibility complex (MHC) class I could be involved in predisposing a pregnant mare to abortion.

“MHC class I genes determine the animal’s ‘tissue type’—like people who receive organ transplants where the donor and recipient need to have matching tissue types,” she explained. “In addition, the MHC class I genes determine what antigens (or proteins) from the virus ultimately get presented to the mare’s cytotoxic T cells to fight the infection.

“Some of these genes,” she added, “can also enable the virus to enter host cells