Comparison of digestive capacity in broilers raised on diets with or without soybean meal

The objective of this study was to investigate the digestive capacity of broilers raised on diets with or without soybean meal, and evaluate the impact on the determination of metabolizable energy (ME) in feed. Two hundred and eighty-eight 7-day-old Arbor Acres male broilers were divided into 6 blocks based on initial body weight (BW). Within each block, 48 broilers were randomly assigned to one of the two types of diet: a corn-soybean meal diet (CSMD) and a corn-based soybean meal-free diet (CSMFD) containing alternative plant proteins (peanut meal, cottonseed meal, and rapeseed meal). Growth performance and physiological parameters of digestive fluids were compared between broilers raised on CSMD and CSMFD. Additionally, the two groups of broilers raised on either the CSMD or CSMFD, along with two test diets (CSMD or CSMFD) for ME determination, were used in a 2 × 2 factorial arrangement with a completely randomized design. An in vitro digestion method was used to quantify the potential digestible energy (PDE) in broiler excreta. The broilers raised on CSMFD had reduced average daily feed intake and average daily gain throughout the entire experimental period compared to those raised on CSMD (P < 0.05). The chymotrypsin activity in jejunal fluid on day 21 and chymotrypsin activities in both jejunal and ileal fluids on day 35 were greater in broilers fed CSMD compared to those fed CSMFD (P < 0.05). From 38 to 42 days of age, the broilers previously raised on CSMD had reduced PDE in excreta when fed CSMD test diet, compared to those previously raised on CSMFD (P < 0.05). Additionally, a numerically greater ME of CSMD was observed in broilers previously raised on CSMD compared to CSMFD. These findings indicate that the dietary protein source influences the BW and activities of certain digestive enzymes in broilers. The reduced digestive enzyme activities associated with broilers raised on CSMFD may reduce the ME of a high-PDE diet, thereby diminishing the digestive capacity of broilers during the finisher phase.