Meta-analysis of dietary and animal factors influencing mean retention time of digesta in the broiler chicken gastrointestinal tract

Chicken meat is an important source of protein for human consumption. Therefore, changes in production have been made through management, diet formulation, and genetics to meet increasing global demand. Part of improving feeding program efficiency involves understanding how factors affect nutrient digestibility and animal performance. In particular, understanding the mean retention time (MRT) of digesta in the gastrointestinal tract (GIT) is crucial as it can affect feed intake, gut fill, nutrient digestion, absorption, fermentation, nutrient bioavailability, and utilization. Therefore, a systematic literature search and meta-analysis was conducted to investigate the influence of diet nutritional composition and bird characteristics on MRT in broiler chickens. From the 31 studies identified that met inclusion criteria, data such as the metabolizable energy (ME, kcal/kg of feed) and crude fiber (CF), crude fat (CFa), crude protein (CP), starch, acid detergent fiber (ADF), and neutral detergent fiber (NDF) content (in g/kg of feed of the diet) were collected. Bird characteristics such as production phase and breeding company were extracted. Separate mixed models for different GIT sections (jejunum, ileum, total small intestine, total GIT) were developed in SAS using study as a random effect and combinations of dietary nutrients and bird characteristics as fixed effects. Breeding company and production phase were forced into each model as fixed effects to account for differences in the birds used across studies. Increasing ME was related to decreases in MRT in all small intestine compartments (all p < 0.05). Increasing CP was related to shorter MRT while increasing CFa, CF and ADF were related to increases in MRT in the jejunum (all p < 0.05). Increasing CP saw similar results for the ileum and entire small intestine (both p < 0.05). Other nutritional components of the diet were not found to be significantly related to MRT (p > 0.05). Through this work, better understanding of the factors that affect digestion are established and equations predicting MRT based on diet and animal can be made and contribute to the development of digestion models for broilers.