PSVIII-21 - Meta-analysis of nutritive factors influencing mean retention time of digesta in the gastrointestinal tract of broiler chickens

Abstract: Broiler chicken meat is an important source of food protein for human consumption globally. Over the last several decades, dramatic changes have been made to broiler genetics, management, and nutrition to increase production efficiency. Different feeds with varying nutrient composition have been researched to target goals such as improving growth and feed conversion ratio. Part of understanding and further improving these feeding programs involves understanding the effects of the feed on nutrient digestibility and animal performance. As such, models are a key tool in the wholistic evaluation of diet, genetics, and management interactions. Towards developing a mechanistic digestion model for broilers, knowledge of mean retention time (MRT, min) of digesta in the gastrointestinal tract (GIT) across a variety of diets is required. To understand the relationship between MRT in broilers and their diet, a systematic literature search and meta-analysis was conducted where 34 articles were found to meet the inclusion criteria. MRT in these studies was measured in various parts of the GIT where 7 studies reported MRT in just one segment (e.g. jejunum), 12 studies reported MRT in multiple combined segments (e.g. jejunum + ileum) and 21 studies reported MRT of the entire GIT. Birds used in these studies included those in the starter, grower, and finisher phases as well as breeders. Nutritional composition of the diets was represented by data on metabolizable energy (ME, kcal/kg), crude fiber (% DM), crude fat (% DM), crude protein (% DM) and calcium (% DM) that was consistently reported across studies. A mixed model (PROC MIXED, in SAS), treating study as a random effect, and using a subset of the data collected where MRT was reported for the entire GIT, and limited to grower and finisher phases, was used to examine the relationship between the diet composition and MRT. Only ME (F_1,28.1=4.25, p=0.0486) was found to be significantly related to MRT, where an increase in one kcal/kg of ME resulted in a decrease of MRT by 0.091 minutes (within the range of 2749 to 3507 kcal/kg ME). Other nutritional components of the diet were found to have no significant relation to MRT (all p>0.05), though next steps will examine how the source of ME (fat vs starch vs fiber) impacts this relationship. Although other factors (such as age and feed intake) are still to be considered, the initial results from this study provide valuable insights into how nutritional composition of poultry feeds relates to MRT. Further investigation will also quantify this relationship within segment of the GIT. This work not only provides valuable information to nutritionists, but also lays the groundwork for empirical model development to predict MRT of poultry feed, essential to poultry nutritional models.