Abomasal secretion and motility in sheep : effect of diet and digesta components

In sheep fitted with re-entrant cannulas in the proximal duodenum, secretory rates of acid in the abomasum increased with protein or buffering content of the rations.In sheep fitted with an abomasal infusion tube and with duodenal re-entrant cannulas, proteins and inorganic buffers continuously infused into the abomasum stimulated acid secretion. Intra-abomasal infusion of amino acids had little effect on secretion of acid. Soya protein, partly hydrolysed in advance, was a more active stimulator of acid secretion than unhydrolysed soya protein. Volatile fatty acids and L-lactic acid stimulated acid secretion slightly.After infusion into the abomasum of soya protein, partly hydrolysed in advance, or of a KHCO ₃ buffer, concentration of gastrin in blood plasma increased. Infusion of α-alanine, β-alanine and glycine did not alter gastrin concentration.Pepsin activity of duodenal digesta did not correspond with that to be expected from abomasal secretion of pepsinogen. In tests in vitro, proteins inhibited pepsin activity.Blood flow in the abomasal mucosa, as measured by aminopyrine clearance, was not related to abomasal secretion of acid. Mucosal blood flow was measured in a feeding trial and after intra- abomasal infusion of soya protein or of a KHCO ₃ buffer into the abomasum.Abomasal antral and pyloric contractile activity, recorded in sheep fitted with strain gauges, were regular. The pattern depended little on feeding regime, and was not affected by continuous infusion of soya protein into the abomasum. Discontinuous infusions of soya protein, of a KHCO ₃ buffer, of amino acids, and of fatty acids into the abomasum showed minor effects on antral and pyloric contractile activity. The motility data indicated that propulsion of abomasal digesta into the duodenum cannot be explained by frequency and intensity of antral and pyloric contractile activity only.