Mechanism of reflex regulation of eructation in sheep

Abstract

Forestomach motility and its association with eructation was studied in sheep and some of the factors affecting the primary and secondary cycle contractions of the reticulo-rumen and eructation were investigated.

A new technique for recording the reticulo-ruminal movements from discrete locations was developed. This made it possible to assess the involvement of reticulo-ruminal musculature in the primary and secondary cycle contractions. It was found that the primary cycles started with a biphasic contraction of the reticulum and progressively involved the cranial the middle and the caudal regions of the dorsal rumen, followed usually by a contraction of the ventral rumen. The secondary cycles usually started in the caudal wall of the caudo-ventral blind sac and progressively involved the caudal and then the cranial regions of the dorsal rumen, followed nearly always by a contraction of the ventral ruminal sac.

Eructation was principally associated with the secondary cycle contractions of the dorsal rumen and took place when the contraction had reached its peak. Eructation occurring during a primary cycle was rare. The frequency and the amplitudes of reticulo-ruminal contractions for the primary and secondary cycles and the frequency of eructation varied with the activity of the animal, he. resting, ruminating or eating. Eating exerted an over-all stimulatory effect on the motility of the reticulo- rumen and the frequency of eructation.

Gaseous distension always increased the frequency of secondary cycle contractions and eructation more than the primary cycle contractions of the reticulo-rumen which were not affected at moderate distension.

The latter responded at higher degrees of free gas distension. The excitatory effects of anaesthetic bag distension in the dorsal rumen were more pronounced for the primary cycle contractions than the secondary cycle contractions of the forestomach. Extreme distension with free gas depressed the amplitudes of reticulo-ruminal contractions. The effect was more pronounced on the secondary cycle contractions of the rumen. Extreme distension with an anesthetic bag was more inhibitory for the primary cycle contractions. Evacuation of ruminal gases depressed the cyclic activity of the forestomach. The over-all decrease was more apparent in the secondary cycle contractions than in the primary cycle contractions.

Addition of acid or alkali solutions into the rumen produced low or high pH of the rumen contents respectively. At these values of pH the primary cycle contractions of the reticulo-rumen were either depressed or completely abolished while secondary cycle contractions of the rumen accompanied by an eructation continued, though with reduced force and frequency.

It is concluded that the primary and secondary cycle contractions of the reticulo-rumen are under independent nervous control and that the association with eructation is regulated through its the presence of secondary cycle contractions of the rumen, whose frequency and amplitudes are determined by the degree and type of distension.