The effect of acute unilateral inflammation of the equine temporomandibular joint on the kinematics of mastication.

This research investigates how temporary unilateral inflammation in a horse’s temporomandibular joint (TMJ) can affect the animal’s eating patterns. Using an experimental study with six healthy horses, the study found that inducing inflammation in the TMJ significantly altered the horses’ masticatory cycle, causing avoidance behaviors, food spilling, and loss of feed efficiency in some cases.

Study Design and Methodology

• In this controlled experimental study, the researchers used six horses of varying ages, all possessing normal dentition.
• An optical motion tracking system was utilized to accurately monitor and record the horses’ chewing movements over three-minute intervals as they ate grass hay.
• The inflammation was induced using lipopolysaccharides (LPS) that were injected into the left TMJ of each horse.
• After six hours, the horses’ masticatory cycles were evaluated again.

Findings of the Study

• Four of the six horses developed an effusion, or swelling, in the TMJ that had been injected with LPS. Two of these four horses also began “quidding,” which refers to the dropping of partially chewed food from the mouth.
• All the horses that were injected on their initial side of the powerful chewing stroke switched sides, while the rest, who were injected on the opposite side, did not change.
• All horses exhibited a reduced vertical pitch or opening, of their mandibles, though their rostrocaudal movement remained unchanged.
• Though the timing of the mandible’s rostrocaudal movement relative to the masticatory cycle was altered, the amount of lateral movement remained the same post-injection.

Conclusions of the Study

• Inflammation, induced via LPS injection into the TMJ, resulted in substantial deviations in the horse’s masticatory cycle compared to the baseline measurements.
• The inflammation also led to quidding and a decrease in feed efficiency in a few horses.
• Despite this, the horses continued to eat, favoring the use of the unaffected side of the mandible.