Amino Acid Balanced Compound Low-Protein Diets Improve Resource Efficiency in Sanhua Goose Production: Impacts on Metabolism, Gut Health, and Microbial Diversity

This study investigated a compound low-protein diet (CLPD) strategy to reduce soybean meal (SBM) dependency in meat geese. Diets were formulated with crude protein (CP) levels decreasing from 16.5% (corn-soybean meal diet, CSD) to 9.8%, incorporating alternative ingredients such as rapeseed meal, corn distillers dried grains with solubles (DDGS), broken rice, and rice bran. All diets were balanced for limiting amino acids (lysine, methionine, threonine, and valine) through supplemental synthetic amino acids. A total of 192 four-week-old Sanhua geese were randomly assigned according to a single-factor completely randomized design to four dietary treatment groups: the 16.5% (CSD) group and three CLPD treatment groups (14.0% CP, 11.5% CP, and 9.8% CP). Each treatment consisted of six replicate pens with eight geese per pen. During the six-week trial, evaluations included growth performance, organ weights, nutrient digestibility, serum biochemistry, amino acid profiles, intestinal morphology, and cecal microbiota composition. Results demonstrated that compared to the 16.5% (CSD) group, the 11.5% CP (CLPD) group significantly improved final body weight (<i>p</i> < 0.05), average daily gain (P_Linear < 0.01, <i>p</i> < 0.05), and feed conversion efficiency (P_Linear < 0.01, <i>p</i> < 0.05), alongside enhanced apparent digestibility of crude protein and amino acids (P_Linear < 0.01, <i>p</i> < 0.05). Organ weights were generally stable, though the 9.8% CP (CLPD) group showed reduced liver weight (<i>p</i> < 0.05) and increased abdominal fat (P_Linear < 0.01, <i>p</i> < 0.05). Serum levels of low-density lipoprotein cholesterol increased (P_Linear < 0.05, <i>p</i> < 0.05). Intestinal morphology improved in the duodenum and jejunum: in the duodenum, villus height and villus-to-crypt ratio were significantly increased, and crypt depth was significantly decreased (P_Linear < 0.01, <i>p</i> < 0.05); in the jejunum, villus height was significantly increased (<i>p</i> < 0.05) and crypt depth was significantly decreased (<i>p</i> < 0.05). Cecal microbiota alpha diversity remained consistent. The dominant genera in the 9.8% CP (CLPD) group were <i>unclassified_Oscillospiraceae</i> and <i>unclassified_Ruminococcaceae</i> (<i>p</i> < 0.05), among which, <i>Megamonas</i>, <i>Prevotellaceae_Ga6A1_group</i>, and <i>Rikenellaceae_RC9_gut_group</i> dominated in the 16.5% (CSD) group (<i>p</i> < 0.05). These findings indicate that a compound low-protein diet (CLPD) with 11.5% CP, precisely balanced for limiting amino acids, supports optimal growth performance, improves nutrient utilization, and maintains intestinal health in meat geese. Overall, this offers a viable approach to easing SBM reliance in poultry nutrition while enhancing resource efficiency.