A radiological study of the patterns of contraction and digesta movement in the alimentary tract of the sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University

Abstract

A radiological study of the motility of the stomach and small intestine and the movement of their contents was undertaken to define, in detail, the forms of contractions and their effect on digesta. A variety of radiographic techniques were employed depending on the information sought. For continuous observation over extended time periods fluoroscopy was used which combined image intensification with a closed circuit television chain and video-tape recorder. For detailed analysis of contractions or movements radiographic cine-film, serial spot-films or plain radiographs were used. The radiographic contrast of digesta was enhanced by the addition of barium sulphate which was either administered orally or introduced to a particular site through a fistula or cannula. Stainless steel wire loops sutured into particular structures formed radio-opaque markers of sites of specific interest. In the study of the small intestine the electrical activity of the intestinal wall was recorded in conjunction with the radiographic techniques. The sequential contractions of the compartments, folds and pillars of the reticulo-rumen that comprise A and B sequences were found to be the result of waves of contraction migrating across reticulo-rumen caudally from the reticulum and cranially from the caudal ventral blind sac. The different character of A and B sequences in the fasted and replete animal reflected waves of contraction that migrated at different speeds over varying distances. The pattern of digesta flow within the reticulo-rumen followed a consistant pattern suggesting that the selection of digesta for onward passage to the omasum was by flotation. The pattern of gas movement suggested that the displacement of gas from the dorsal rumen into the caudal ventral blind sac initiated B sequences of contraction. No movement of the omasum was observed radiographically other than that imposed by contiguous structures, especially the reticulum. The most prominent feature of abomasal motility was peristaltic contractions moving towards the pylorus at a frequency which remained constant irrespective of the degree of abomasal distension. Abomasal distension was found to inhibit A sequences in the reticulo-rumen and to alter the pattern of digesta movement in the small intestine. The presence of peristaltic contractions on the abomasum was related to activity in the duodenum and orad jejunum. The movement of digesta in the small intestine was of two basic forms; patterns of movement that were characteristic for a particular region and migrating patterns of movement. These patterns were associated with the electrical activity recorded from the intestinal wall. Alterations to the flow of digesta through the small intestine caused by increased flow through the pylorus, additions or subtractions through T cannulae or the insertion of re-entrant cannulae at certain sites caused marked changes in the patterns of digesta movement. It was concluded that the basic motility pattern in both the stomach and the small intestine is migrating waves of contraction. The pattern in which these waves occur results from interactions between (a) the flow of digesta, (b) the degree of distension either local or in adjacent regions and (c) the pace-setter - imposed via the vagus, on the reticulo-rumen and by the slow wave frequency on the abomasum and small intestine.