Description of a Dynamic In Vitro Model of the Dog Gastrointestinal Tract and an Evaluation of Various Transit Times for Protein and Calcium

In order to manufacture complete and balanced dog diets, it is important to know the nutrient requirements of dogs and the availability of these nutrients from food. As pet food manufacturers are restricted in their options for (invasive) animal studies, due to ethical constraints, it is important to have alternative methods for researching the effects of various dog diets. To simulate the gastrointestinal tract of the dog, the dynamic gastrointestinal tract model developed by Minekus et al. was further developed and modified in this study. The model consists of four compartments which simulate the stomach and small intestine (duodenum, jejunum and ileum). Each compartment is made of glass, with a flexible inner wall. This wall can be compressed by increasing the pressure of the surrounding water, mimicking the peristaltic movements and mixing seen in vivo. The model is computer-controlled to simulate physiological parameters such as pH, transit time and secretion of digestive juices, as derived from the literature. Gastric meal delivery and the effects of intestinal transit time on protein digestibility and availability for absorption of calcium from dog food were studied to evaluate the model. The gastric meal delivery of dry dog food was identical to a preset curve, which was based on in vivo data from healthy dogs. The emptying time for canned dog food was somewhat slower than the preset values, probably due to the viscosity of the meal. The differences between the preset values and the measured delivery were not significant. The digestibility of protein and the availability of calcium for absorption increased with a longer transit time. A significant difference was found between medium and slow transit times for the nitrogen content in the ileal delivery effluent and the jejunal dialysates (p < 0.05). The same trend was seen for calcium (not significant). The overall conclusion is that the model is a useful tool for mimicking the gastrointestinal tract of dogs. Parameters such as pH, transit time and enzyme activity can be mimicked and can be kept within a physiological range.