Horses eating a diet consisting mostly of pellets or grain could require more dental maintenance than horses eating predominantly hay or pasture grasses, according to researchers at Michigan State University who used motion capture techniques to track the movement of horses’ jaws. The results of their study showed that horses use slower, larger movements to masticate (chew) hay than pellets, resulting in a more functional pattern of tooth wear. This means owners with horses eating a diet consisting of mostly pellets might need to have their horses’ teeth checked more often to avoid the development of enamel irregularities.

The researchers used seven horses for the study. An equine dentist had seen all of the horses prior to the study, and none had malocclusions (abnormal contact between two or more teeth, which might have impacted their chewing motion). Twelve markers were placed in identical locations on the horses’ heads, and six infrared cameras placed in a semicircle around the head recorded the chewing motions. The horses ate hay and pellets in random order, with several repetitions of the switch with each horse.

Horses eating hay made larger mandibular movements in all directions (opening and closing vertically, and from side to side when grinding the food). Horses eating hay also took more time to chew each mouthful and chewed with less frequency than those eating pellets. The researchers noted that fibrous food stays on the cheek teeth as the jaw moves, allowing the horse to utilize the full lateral movement of his jaw. They postulated this might explain why the skulls of fossil and undomesticated modern equids, such as zebras and Przewalski’s horses, are rarely found to have the enamel overgrowths that are common in domesticated horses.

“The results of this study support the suggestion that an ample diet, high in the type of roughage consumed by nondomesticated horses, promotes dental health through a greater range of mandibular motion and a slower chewing frequency,” the researchers noted.

They recommended horses fed a large proportion of their diet in the form of concentrates to fulfill their energy requirements be examined for dental irregularities more frequently than those maintained on long roughage.

The study, “Comparison of mandibular motion in horses chewing hay and pellets,” was published in the May 2007 edition of the Equine Veterinary Journal. Researchers performing the study included Stephanie J. Bonin, MS; Hilary M. Clayton, BVMS, PhD, MRCVS; Joel L. Lanovaz, PhD; and Tom Johnston, DVM.