Abstract

Infusion into the abomasum of sheep of a mixture of volatile fatty acids partially neutralized with sodium hydroxide (VFA salts) markedly increased the rates of flow of liquor and chloride from the abomasum to the small intestine; buffered mineral salts comprising sodium bicarbonate, sodium citrate and either disodium or dipotassium orthophosphate consistently produced a similar but smaller response. Thcre was little or no effect of the infusions on rumen or omasal outflow. By contrast, infusion of VFA in acid form had no effect on abomasal liquor and chloride flow and the infusion of sodium chloride did not effect liquor flow. The pH of abomasal digesta either decreased slightly or was unchanged when VFA salts wcre infused, but increased with infusion of mineral buffer salts. It is concluded that gastric secretion is markedly affected by the buffering capacity of the digesta entering the abomasum. The VFA entering the abomasum in digesta were estimated to be responsible for the secretion of as much as 60% of the chloride secreted into the organ. High rates of abomasal secretion, induced by intra-abomasal infusion of VFA salts, increased both (i) the amount of digesta in the abomasum and small intestine, (ii) the extent of absorption of calcium and magnesium distal to the omasum, and (iii) absorption from the small intestine of water, chloride and VFA, while decreasing (i) the pH of digesta in some sections of the small intestine and (ii) marker residence time in the proximal half of the small intestine. The rates of flow of both liquor and chloride from the abomasum, together with pH of abomasal digesta, progressively increased with age in animals aged 6, 10 and 30 months; they were still larger in other animals aged 54 months. By contrast, no consistent trends with age were observed with VFA and chloride concentrations in rumen liquor or the flow of metabolites from the rumen. The flow changes are suggested to be the result of changes in gastric juice secretion with age, stimulated at least in part by a corresponding decrease in the rate of absorption of buffering substances in the omasum and/or abomasum.