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 sociability rating) on a five-point scale. The horse scored a 5 if he approached the researcher within two seconds, and he scored a 1 if he never approached or fled the researcher.

Next, the team placed the three novel objects, one at a time, in each horse’s pen. They videotaped the horse’s response to each object for 10 minutes and measured horses’ play behavior based on the equid play ethogram developed by Sue McDonnell, PhD, Cert. AAB, founding head of the Equine Behavior Program at the University of Pennsylvania School of Veterinary Medicine. They also tried to calculate at what point sensory investigation of something new becomes play and estimated that if the horse investigated an object for 13 seconds or more, then he was likely playing.

Based on their observations the team determined that:

  • Older horses investigated and played less, on average, than younger ones.
  • Horses with higher sociability ratings investigated the objects longer than horses with lower ratings.
  • Horses considered the cube as more "fun" than the other objects, approaching it more quickly and playing with it longer. Brubaker theorized that this was because the cube was collapsible and the horses seemed to enjoy dissembling it.
  • There was no significant difference between mares’ and geldings’ latency (time it took to approach the object) or duration of interest, which Brubaker said was interesting because adult mares rarely play socially.

These results all "support the hypothesis that domestic horses display behavioral neoteny," Brubaker concluded.

From a practical perspective, she added, "I think it would be worth our effort to consider this possible behavioral neoteny. Aged horses, even a 29-year-old, may still be curious and playful toward new things. We can maybe factor that into our management and training."