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 nutri ents from food. As pet food manufacturers are restricted in their options f or (invasive) animal studies, due to ethical constraints, it is important t o have alternative methods for researching the effects of various dog diets . To simulate the gastrointestinal tract of the dog, the dynamic gastrointe stinal tract model developed by Minekus et al. was further developed and mo dified in this study. The model consists of four compartments which simulat e the stomach and small intestine (duodenum, jejunum and ileum). Each compa rtment is made of glass, with a flexible inner wall. This wall can be compr essed by increasing the pressure of the surrounding water, mimicking the pe ristaltic movements and mixing seen in vivo The model is computer-controlle d to simulate physiological parameters such as pH, transit time and secreti on of digestive juices, as derived from the literature. Gastric meal delive ry and the effects of intestinal transit time on protein digestibility and availability for absorption of calcium from dog food were studied to evalua te 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 emptyi ng time for canned dog food was somewhat slower than the preset values, pro bably 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 lo nger transit time. A significant difference was found between medium and sl ow transit times for the nitrogen content in the ileal delivery effluent an d the jejunal dialysates (p < 0.06). The same trend was seen for calcium (n ot significant). The overall conclusion is that the model is a useful tool for mimicking the gastrointestinal tract of dogs. Parameters such as pH, tr ansit time and enzyme activity can be mimicked and can be kept within a phy siological range.