Interplay between dietary crude protein level and starch structure: production performance and amino acid utilization of geese

A total of 240 healthy 35-day-old male Jiangnan White geese were used in a 2 × 2 factorial experiment to evaluate the effects of dietary crude protein ( CP ) level and starch structure on growth performance, intestinal digestive function and amino acid metabolism. Two CP levels (16% and 14%) and two amylose/amylopectin ratios ( AM/AP ratio , 0.34 and 0.44) were tested from 35 to 63 days of age. Lowering dietary CP improved body weight, average daily gain, and feed efficiency, but increased abdominal fat and mesenteric fat deposition and impaired protein nutritional status, as indicated by reduced serum total protein and globulin and increased glucose and creatinine levels. Low-protein diets also increased jejunal α-amylase and trypsin activities and ileal trypsin activity, while reducing serine digestibility. Increasing the dietary AM/AP ratio improved body weight at 63 d, average daily gain, feed efficiency, breast muscle yield, and reduced abdominal fat deposition. It also increased jejunal villus height, decreased jejunal α-amylase and maltase activities, and increased ileal chymotrypsin activity. Most apparent amino acid digestibility values were numerically improved by the higher ratio. Overall, moderate CP reduction improved growth but promoted fat deposition, whereas a higher AM/AP ratio enhanced growth, carcass traits, and intestinal function, partly offsetting the negative effects of low-protein diets.