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Intestinal Passage and Its Relation to Digestive Processes

SUMMARY Despite an effective nutrient retention, impaired digestibility is frequently observed. This review aims to give an overview of retention time of material through the digestive tract in an attempt to reveal mechanisms relating flow and retention of material to the digestive process. The mean retention time based on marker content in the different segments of the digestive tract or measured as time of 50% marker excreted is remarkably short at between 5 and 6 h, but varies considerably due to method used, diet composition, and feeding pattern. Mean retention time in the small intestine is commonly reported to be around 3 h, with 1 h retention time in the tract proximal to Meckel's diverticulum, and is less affected by diet or feeding pattern. The mechanism explaining a high nutrient digestion and absorption despite this astonishingly short time is still a puzzle. A selective flow and reflux of material throughout the small intestine seems to be a potential mechanism, but more research is needed in this important and fascinating area of poultry research.