The sequential contractions of the rumen associated with eructation in sheep.

1. The orderly sequential movements of the reticulum and the rumen were studied in conscious sheep by electromyography using enamelled stainless-steel wires implanted in various regions of the stomach wall and by recording mechanical changes within the various parts of the organ. Electrical activity of the rumen and/or pressure changes were related to eructation when the animals were at rest, feeding or ruminating.2. Secondary contractions of the rumen were found to originate in the ventral blind sac immediately following a primary contraction or independently. The wave of contraction originating in the ventral blind sac was seen to pass in a circular manner to the dorsal blind sac, the dorsal sac, the ventral sac and finally once more to the ventral blind sac. Eructation occurs at the end of the contraction of the dorsal sac. In each case, the time required to initiate the secondary cycle depended on the strength of contraction of the ventral blind sac.3. Sustained gaseous distension elicited numerous secondary contractions of the rumen concurrent with a lower frequency of reticular contractions. Although some secondary contractions were incomplete, all began with contraction of the ventral blind sac and were associated with eructation.4. Chemical stimulation of the rumen by fatty acids at pH 5.5-5.9 increased the ratio of secondary to primary contractions of the rumen to a varying extent depending on their initial rate.5. It was concluded that the seemingly random occurrence of a secondary cycle of the rumen was dependent on the activity of the ventral blind sac and its pattern could be altered by both mechanical and chemical stimulation.