If you’ve ever come across a particularly big-eyed, dish-faced horse, maybe you’ve thought to yourself, "He has such a baby face." We see these physical manifestations of youth in many adult species (think of dogs bred to retain a puppylike appearance), but in horses this retention of juvenile traits in adulthood might also be evident in their behavior.

The phenomenon is called behavioral neotenization, and it’s particularly common in domesticated animals, although in the literature it’s not clear whether horses exhibit neoteny. So Alexali Brubaker, PhD, of the University of California, Davis, department of psychology, conducted a study to evaluate and quantify youthful play behavior in adult horses. She presented her results at the 9th Annual International Society for Equitation Science, held July 18-20 at the University of Delaware, in Newark.

Horses respond to novel objects and situations with various levels of fear and curiosity. If horses have undergone neotenization, Brubaker explained, "accommodating juvenilelike traits such as curiosity could potentially improve well-being of adults."

To investigate whether horses have retained these juvenile behavioral traits, Brubaker and colleagues assessed the play and curiosity (novelty-seeking) responses of 46 adult horses (25 mares and 21 geldings, primarily Thoroughbreds and Quarter Horses ages 3-29) housed in their home outdoor pens when presented with three novel objects: a yoga ball, a plastic saucer, and a hollow cube made of PVC pipe.

First, a researcher unfamiliar to the horses entered each pen and scored each horse’s response (its soci