how horses chew

Don’t scarf down your food, Rusty. It’s not like you’re a cow and get to chew it a second time.

Fortunately, that’s not something we have to tell most horses. Recent study results show that horses are very efficient chewers with a rhythmic chewing pattern similar to that of cows.

Cows, camels, and many other herbivores are ruminants—meaning they chew food, swallow it, and then return the parts that still require chewing back to the mouth for further chewing and swallowing. Horses belong to a group of herbivore species that don’t do this. They chew, swallow, digest, and that’s it.

Recently, Swiss researchers compared chewing patterns in six Warmblood riding horses to six heifers and six camels. They fed each one the same amount of hay from the same bale and fitted each animal with a special research halter that detects chewing pressures and rhythms.

They found that the camels and cows chewed hay in an irregular pattern the first time, with stops and starts and large and small chewing motions, said Marcus Clauss, a professor at the Clinic for Zoo Animals, Exotic Pets, and Wildlife at the University of Zurich’s Vetsuisse Faculty, in Switzerland. But after they’d swallowed that food, let it sit for a while, and brought it back up again, they chewed in a more consistent, rhythmic way that broke down the food pieces more effectively.

Horses, on the other hand, chewed efficiently as soon as they put the hay in their mouths, he said. In fact, their chewing was so consistent and rhythmic, the pressure halter’s data analysis system confused the horses’ chewing with “ruminating chewing”—the kind of chewing ruminating animals do the second time (after the food comes back into the mouth).

“Although horses are not ruminants, they fragment their food with the same rhythmic chewing movements as cows do during rumination,” said Marie Dittmann, a PhD candidate at the University of Zurich and ETH Zurich.

Horses chew so efficiently that the size of food that goes into their stomachs is about a tenth of the size, sometimes smaller, than what goes into cow and camel stomachs the first time, Clauss said. Cows and camels break the food pieces down to smaller sizes only after they’ve chewed it multiple times.

In the study, the horses also consumed their hay faster than the cows and camels did, said Clauss. Cows and camels appear to spend more energy with their inconsistent chewing and swallow a lower quantity of hay, with larger food pieces, than horses do in the same amount of time.

“Horses do not have a second chance to rechew something that is hard to digest,” he said. “For that reason, they have to masticate (chew) very thoroughly when eating. That obviously works best with rhythmic and even movements.”

However, horses have to deal with more grit and dust, which wears away at their teeth, than ruminants do, he said. That’s because the ruminants don’t “get down to the nitty-gritty” of chewing until after the food has soaked—and gotten “washed”—in their stomachs for a few hours. By the time it comes back up for a second chewing, the dust and grit is gone.

What’s more, horses pull up grass and hay with their teeth, biting it to rip it out of the ground or feeder, Clauss said. Cows and camels pull up the forage with their tongues, limiting their teeth’s contact with dirt, dust, and other kinds of grit.

He said these findings don’t necessarily mean we need to change the way we care for our horses’ teeth. Rather, he said, it helps us better understand how and why their teeth wear as they do.

The study, “Ingestive mastication in horses resembles rumination but not ingestive mastication in cattle and camels,” was published in the Journal of Experimental Zoology, Part A, Ecological and Integrative Physiology.