Horses and Dogs Understand and Adapt to Each Other in Play
A predator. A prey animal. And the pasture, their playground.

If you’ve ever seen dogs and horses interact in playful behavior, you’ve glimpsed a natural phenomenon. These two highly different, yet highly domesticated mammals can play together, communicating their intentions of playing and reading and mimicking each other’s facial expressions, according to Italian researchers.

“There are behaviors that go beyond the very nature of the animal (prey/predator),” said Veronica Maglieri, an ethology student in the Department of Biology at the University of Pisa, in Italy.

“It’s really amazing to watch animals chasing each other, rolling around, and even biting each other without ever showing any doubt about the playful intentionality of their actions,” she said. “This really gives us an indication of the cognitive complexity of these animals.”

Maglieri and a team led by Elisabetta Palagi, PhD, professor at the University of Pisa, evaluated 20 YouTube videos of dogs and horses in spontaneous play. They found that, generally, horses and dogs seem to “understand each other” when it comes to play, and they adapt their behaviors accordingly.

“Self-handicapping” is common in horse-dog play, Maglieri said. Self-handicapping, already known in dog-to-dog play, involves the act of modifying behavior or position to reduce one player’s strengths. Similar to a parent giving a child a head start in a race or a stronger chess player removing pieces before starting a chess game, animals tend to reduce their strengths in play sessions to make the game more “fair,” she explained. Her group’s study showed, for the first time, that even horses and dogs do this for each other.

For example, dogs used their carnivorous teeth and claws less, and horses reduced their height by lowering or lying down, Palagi explained. Both species tended to lie on their backs, exposing themselves in vulnerable ways.

“These patterns would be dangerous for the animal if they were made in nonplayful contexts, and the fact that they do them tell us that our subjects blindly trusted each other,” she said. “They performed this pattern despite the risks associated with them, and they use them to entice the other subject to play and to communicate their playful intentions. Self-handicapping patterns are a peculiar behavior and indicate not only the great motivation to play but also the animal’s perception of itself.”

Despite the species’ many physical differences, self-handicapping efforts were balanced, she added. “Our results show that the number of self-handicapping patterns were similar between dogs and horses, and this is amazing because they indicate a perfect synchronization between the two species,” said Maglieri.

Facial expressions were also a critical part of the interspecies play, said the researchers. They tended to show frequent “relaxed open mouth (ROM)” behavior—where they held their mouths open without any kind of tension—as well as “rapid facial mimicry (RFM)”—in which they echoed facial expressions made by the playmate. It appears to have a role in “mood-sharing during social interactions,” the researchers stated.

“The presence of RFM between dogs and horses leaves us speechless with regard to animals’ communication skills and shows us how much we still have to discover,” Palagi said. “If horses are able to communicate so finely with a subject of another species, who knows what they can do when communication takes place between members of the same species. It would be really interesting in the future to study horse play sessions, as well.”

The researchers’ work was initially inspired by a “particularly beautiful” YouTube video that showed frequent facial expressions (easier to see frame-by-frame, Maglieri added) as well as self-handicapping, with both species lying down and rolling onto their backs, Maglieri said.

“This work has fascinated us right from the start,” she said. “We do not believe that playing behavior can take place in such a natural and relaxed way between subjects so different unless there is a great deal of trust between them. If people are lucky enough to come across this behavior in their environments, we hope that they will look at it with a new awareness and enjoy the whole world that lies behind such ‘simple’ behavior as the play is.”