Direction of jaw movement in dairy cattle during the rumination period

Jaw movements in dairy cattle were observed during rumination. The directio n of jaw movement was recorded to determine the frequency in three phases: the first jaw-opening movement (FJM) which serves to keep the major pan 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 se rve to repeatedly jumble and grind the bolus, and the last jaw-opening move ment (LJM) which serves to prepare the bolus for swallowing. Five dairy cat tle 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) wa s a one-way movement, either left or right depending on the position of eac h bolus in the oral cavity (the storage side). However, the direction of MJ M 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 move d from the other side to the storage side. Furthermore, it was found that t he direction of MJM is not always the same from one rumination period to an other. 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 remast icating most of the boli during a given rumination period, but there were c ases in which cattle changed the direction of jaw movement between ruminati on periods. (C) 1999 Elsevier Science B.V. All rights reserved.