If you have broodmares, you know that housing them next to stallions or geldings could be dangerous—for the fetus: Czech researchers recently determined that pregnant mares can abort their fetuses as a stress response to prevent future infanticide.

In the wild, some stallions have been observed killing foals they did not sire. Even in domestic settings, mares—consciously or subconsciously anticipating that event—might abort their fetuses if they suspect infanticide could happen, explained Ludek Bartos, PhD, professor and department head in the Department of Ethology of the Institute of Animal Science in Praha Uhrineves, and of the Department of Animal Science and Ethology in the Faculty of Agrobiology, Food, and Natural Resources at the Czech University of Life Sciences in Praha.

The mares appear to be more likely to abort when they’re separated by a fence from a stallion or gelding, Bartos said. Somehow the mare recognizes that, because of the separation, the foal she’s carrying is not the product of that male, he explained. But she won’t recognize the fence as being sufficient protection for her future foal. To stop that male from killing her foal after birth, her body creates a stress reaction that leads to the unborn foal’s death.

“The stress is based on the fear the male ‘next door’ will commit infanticide one day, once she delivers her foal,” he said. “She may suffer from all known processes associated with stress and/or triggered by the stress. The final concrete abortogenic mechanism thus may be variable, but fatal for the embryo anyway