Jaw movements in dairy cattle were observed during rumination. The direction of jaw movement was recorded to determine the frequency in three phases: the first jaw-opening movement (FJM) which serves to keep the major part of the bolus on one side of the oral cavity, the main jaw-opening and -closing movements (MJM), from the second movement to the penultimate one, which serve to repeatedly jumble and grind the bolus, and the last jaw-opening movement (LJM) which serves to prepare the bolus for swallowing. Five dairy cattle were monitored in trial 1 to record FJM, MJM and LJM, and 16 cows were monitored in trial 2 to record MJM. It was found that the direction of FJM and MJM during a single rumination period (time spent chewing one bolus) was a one-way movement, either left or right depending on the position of each bolus in the oral cavity (the storage side). However, the direction of MJM was opposite to that of FJM, because in the case of MJM, the jaw-opening activity scattered the bolus, so it moved from the storage side in the oral cavity and the jaw-closing activity ground it down while it was being moved from the other side to the storage side. Furthermore, it was found that the direction of MJM is not always the same from one rumination period to another. It was suggested from this study that dairy cattle tend to show jaw movement in a constant one-way direction, either left or right, when remasticating most of the boli during a given rumination period, but there were cases in which cattle changed the direction of jaw movement between rumination periods.
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