Effects of various diets on gastric tone in the proximal portion of the stomach of horses

Objective. To assess gastric tone in the proximal portion of the stomach in horses during and after ingestion of 4 diets (2 diets of grain and 2 diets of hay). Animals. 6 adult horses. Procedure. A polyester bag with a volume of approximately 1,600 ml was inserted through a gastric cannula into the proximal portion of the stomach of each horse. Internal pressure of the bag was maintained at 2 mm Hg by use of an electronic barostat, and changes in bag volume were recorded before, during, and after horses consumed diets of grain or hay. Each horse was fed 0.5 and 1.0 g of grain/kg and 0.5 and 1.0 g of hay/kg. Changes in bag volume measured by use of the barostat were indirectly related to changes in tone of the gastric wall. Results. Food intake caused a distinctly significant biphasic increase in volume. The first phase was during active ingestion, which was followed shortly by a second, more prolonged postprandial phase. The ingestion-related phase of the response to intake of a diet of 1 g of hay/kg was significantly greater than that for the other diets. Conclusions and Clinical Relevance. Ingestion of a solid meal induces a biphasic relaxation response in the proximal portion of the stomach of horses. Magnitude of the ingestion-related phase may be determined by size of the meal.