They’re all horses, yes. But that doesn’t mean that baby horses act like big horses when they’re in pain.

According to Dutch scientists, foals express pain differently from the way adult horses do. And because of that, they need their own pain-related facial expression scale that’s unique to baby horses.

A good understanding of pain levels that foals are experiencing can help people recognize problems, manage pain, and optimize drug dosing, said Thijs van Loon DVM, PhD, Dipl. ECVAA, assistant professor at Utrecht University, in the Netherlands.

So Van Loon and his fellow researchers took videos lasting up to 60 seconds of 20 foals, ranging from 1-2 days old  up to six months of age in The Netherlands, Germany, and Ireland that had known painful conditions, like injuries, colic, or post-operative pain, before and after pain medication. They also filmed 39 healthy foals as controls. They then showed the videos to three observers who were unaware of which foals were healthy and which were not, or whether they had received pain medication or not. The observers were a senior anesthetist and his veterinary students who underwent a two-day training session on identifying different kinds of equine facial expressions.

They found that foals and adult horses share some of the same pain-related grimaces, like keeping the ears facing backwards and tightening the eyelids. However, they also found some major differences.

For example, foals don’t show the whites of their eyes more when they’re in acute pain, although adults do.

As Van Loon explained, that’s probably because foals just show the whites of their eyes all the time. “They’re constantly looking around, turning their heads and looking at different things around them almost continuously,” he said. “You see a lot of eye whites in these foals even when they’re playing or scanning the environment, so this was one of things that we wanted to take to into account and remove from the scale to avoid false positives.”

Foals also don’t show a Flehmen’s response in association with acute pain, unlike adult horses. In fact, healthy foals were actually more likely to make this characteristic upper lip curl than foals in pain were.

“This is also something we know from mature horses already, that the Flehmen response doesn’t necessarily mean that the horse is in pain because it’s a natural behavior,” he said. “But it is something that is especially associated with colic pain in mature horses, and there’s an obvious difference between healthy animals and animals in acute pain (with regard to adult horses). In the foal study, though, we saw a lot of healthy, pain-free foals showing a lot of Flehmen behavior, and this probably has to do with exploring the environment.” Foals exhibit Flehmen behavior from the first day of life and show it frequently enough that it can’t be used as a reliable indicator of pain, van Loon said.

The scientists also noticed that foals don’t often grind their teeth—even when they have them. “This is different from mature animals,” he said. “We didn’t see teeth grinding, either in the neonatal foals with no incisors or the older foals with teeth.”

One thing foals in pain did do that adults in pain didn’t, however, was smack their lips.

Lip-smacking might be one of the ways foals try to “work out the pain for themselves,” according to van Loon. “Maybe they’re trying to look for behaviors that help them, and maybe lip-smacking even leads to rushes of endorphins that help them cope with the pain, but at this point all this is a bit speculative. We just don’t know. ”

Despite the observers’ relative inexperience with recognizing equine behaviors, they all had similar findings when watching each video, Van Loon said. This strong inter-observer reliability indicates that with just some basic training, equine practitioners, breeders, and handlers could all easily assess pain in the foals under their care.

While this pilot study gave good oversight into specific pain-related behaviors in foals, more research is needed to confirm the results, according to Van Loon.

His team also hopes to fine-tune foal pain behaviors, to develop ethograms that are specific to different kinds of acute pain, like colic pain versus musculoskeletal pain. And further down the line, they also hope to create pain scales for chronic pain as well, he added.

Eventually, the results could lead to a foal-specific section on a future version of his research group’s “Equine Pain and Welfare App (EPWA)” mobile application, which owners can download for free.

The study is published in the open access journal Animals and is titled: Objective Assessment of Acute Pain in Foals Using a Facial Expression-Based Pain Scale by Johannes van Loon, Nicole Verhaar, Els van den Berg, Sarah Ross and Janny de Grauw. You can read the full text here.

Download the Equine Pain Face Poster here.

Read about the Horse Grimace Scale – the first pain face scale that was developed.

Learn about other subtle signs of pain