Changes in Senior Horses' Chewing Ability

Horse’s teeth do not grow continually. Rather, they “erupt” and wear over time. By the time a horse reaches his late teens and early 20s, normal age-related changes are occurring within the chewing surfaces of his cheek teeth that cause progressive loss of surface area. Owners need to make dietary changes for their older horses in light of this, and watch for common dental issues seen in this aging population.

The chewing and grinding surfaces of horses’ cheek teeth are rough, due to folds of very hard enamel. They also contain cementum and dentin that surround and fill in the crevices within the enamel folds, respectively. Cementum and dentin are softer than enamel, so they are not useful for grinding feed, especially hay. As a horse ages and wears down his teeth, they get shorter and shorter and their rate of eruption slows.

And as he enters his teens, and certainly by the time he reaches his 20s, the rate of eruption has diminished to the point that new enamel is no longer surfacing to replace the existing enamel. So, these folds begin to wear. The center of each tooth becomes smooth, reducing the horse’s effective chewing surface area. The exposed dentin and cementum continue to wear, eventually causing the tooth to wear down to the gum line. An outer rim of enamel sometimes remains.

How Cheek Teeth Wear as Horses Age
How Cheek Teeth Wear as Horses Age

These series show how cheek teeth wear as horses age. From left to right, you can see how a younger horse’s enamel folds (see arrows) wear down, starting in the center until enamel remains only along the tooth’s outside ridge. The result is a substantial collective loss of grinding ability. | Photos Courtesy Dr. Caroline Niederman

The horse’s mouth works hardest when chewing hay, so all owners of senior horses should monitor:

  1. How well their horse is eating hay, and
  2. The quality and quantity of the horse’s manure.

Unfortunately, the first sign of ineffective chewing is often a choke episode (esophageal obstruction) involving hay. The horse cannot grind the hay to a small enough size but tries to swallow it anyway. Another dangerous consequence of reduced grinding is the development of an impaction within the horse’s gastrointestinal tract. When the teeth aren’t able to do as much grinding, the horse’s small and large intestines have to do more work to make up for it. If they can’t keep up, the hay can build and cause an obstruction. These horses produce less manure, and the fecal balls they do produce will be drier than normal.

Horses with advanced wear drop clumps of hay (called quidding) while eating, especially when it’s stemmy hay. Owners should be able to recognize these easily. Some horses might not even attempt to eat hay that they have figured out is too coarse for them to grind. This leads to the sudden weight loss often seen in horses during their 20s. These horses are chewing hay but more slowly, so over the course of a 24-hour period they are getting fewer and fewer calories from the hay. If the horse is either not consuming any alternative feeds (senior feeds, hay substitutes such as chopped hay or fiber pellets) or they’re being offered in insufficient quantities to maintain body weight, he will lose body condition. Adjusting the diet will reverse this loss, but it can take two to three months for horses to return to an ideal body condition score (a 5 out of 9).

When it comes to caring for senior horses, veterinarians should not only address the common problems seen in these animals but also educate owners about their horses’ chewing capacity. Making dietary changes as horses lose their ability to grind long-stem hay will help prevent weight loss and other issues that can affect this age group.