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Tuesday, June 12, 2012

Diet affects dental needs of horses

Horses should have a yearly dental evaluation, especially if consuming a diet low in forage or high in pellets.

Summarized by B. Allen and K. Martinson, PhD; University of Minnesota

Have you ever wondered if your horse's diet affects their need for dental work? Previous studies have suggested that temporomandibular or jaw joint (TMJ) kinematics (chewing motion) depended on the type of food being chewed or masticated, but accurate measurements of TMJ motion in horses chewing different feeds has not been published. A group of researchers in the College of Veterinary Medicine at Michigan State University set out to determine if the TMJ has a larger range of motion when horses chew hay compared to pellets (grain).

An optical motion capture system was used to track skin markers on the skull and mandible (lower jaw) of seven horses as they chewed hay and pellets. A virtual marker was created on the midline between the mandibles at the level of the 4th premolar teeth to represent the overall motion of the mandible relative to the skull during the chewing cycle.

Frequency of the chewing cycles was lower for hay than for pellets. Excursions (chewing motion of mandible) of the virtual mandibular marker were significantly larger in all three directions when chewing hay compared to pellets. The mean velocity of the virtual mandibular marker during the chewing cycle was the same when chewing the two feeds.

The range of mediolateral displacement of the mandible was sufficient to give full occlusal contact of the upper and lower dental arcades when chewing hay but not when chewing pellets. These findings support the suggestion that horses receiving a diet high in concentrate feeds (grains) may require more frequent dental prophylactic examinations and treatments to avoid the development of dental irregularities associated with smaller mandibular excursions during chewing compared to horses fed a diet high in forages.

In a separate study conducted at Virginia Tech, chewing direction both before and after dental treatments was investigated. Seventeen horses were observed while consuming small portions of mixed grass-alfalfa hay. Chewing direction was determined by the horse's jaw motion as either counter-clockwise or clockwise.

Horses chewed counter-clockwise 60% of the time before dental work and 37% of the time after dental work. While chewing direction varied between the horses, there was a significant effect of lateral excursion on chewing direction with counter-clockwise chewers having a greater left lateral excursion. There was also a trend for clockwise chewers to have greater right lateral excursion. Dental treatment did not appear to have an impact on chewing direction.

The take home message: horses should have a yearly dental evaluation, especially if the horse if consuming a diet low in forage or high in grains (pellets).

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