Studying Behavior in Penn’s Semi-Feral Horse Herd

On 40 acres of Chester County, Pennsylvania’s lush pasture land, close to 90 ponies roam relatively free of human interference. Their social interactions, reproductive behavior, and physical well-being give researchers like Sue McDonnell, founding head of the Equine Behavior Program at Penn’s School of Veterinary Medicine, a window into the lives of horses in a near-natural state.

“We recognize it as such a valuable teaching resource and a research resource to better understand not only the behavior of horses, but their health and welfare,” says McDonnell.

Founded in 1994 at Penn’s New Bolton Center Campus with 26 unrelated ponies—13 of each sex—the herd is considered semi-feral. Though they are confined by fences and receive some preventive health care and supplemental grass hay in winter, the ponies otherwise fend for themselves, foraging on pasture, drinking from natural water sources, and even giving birth without veterinary assistance.

Reproductive behavior is a major focus of McDonnell’s research. She’s observed that, while the population has more than tripled in less than two decades, there is almost no evidence of inbreeding. “The females seem to only breed with the most distantly related males available,” she says.

The ponies also have a unique courtship ritual. “In mate selection mode, they actually go nose-to-nose first and sort of breathe in each other’s breath,” says McDonnell. “Some horse people call it kissing.”

The knowledge gleaned from studying the New Bolton herd may help improve husbandry practices for domestic horses. For example, McDonnell and colleagues have discovered that male horses that only spend time with other males have lower measures of reproductive fitness than males that congregate with females as well—an important consideration for horse breeders when housing their stallions.

To learn more about research on the New Bolton herd, visit the Havemeyer Equine Behavior Lab website:

Text by Katie Unger Baillie
Video by Kurtis Sensenig