Effects of double-low rapeseed meal on growth performance, meat quality, gut microbiota, and nitrogen excretion in Cherry Valley ducks based on low-protein dietary strategies

This study aimed to investigate the effects of low-protein (LP) diet with double-low rapeseed meal (DLR) partially replacing soybean meal (SBM) on the growth performance, meat quality, and nitrogen excretion of Cherry Valley ducks. In a randomized complete block design, a total of 504 one-day-old Cherry Valley ducks with consistent health, weight, and genetic background (body weight = 51.80 ± 1.49 g) were randomly assigned to seven groups (six replicates/group, 12 ducks/replicate). The dietary crude protein (CP) level was reduced in 0.5 percentage point increments, with the amino acid and energy balance maintained. The dietary CP levels were 20.01% (CON), 19.51%, 19.01%, 18.51%, 18.01%, 17.51%, and 17.01% (LP1, LP2, LP3, LP4, LP5, and LP6, respectively) for 1-14 d of age, 17.50% (CON), 17.00%, 16.50%, 16.00%, 15.50%, 15.00%, and 14.50% (LP1, LP2, LP3, LP4, LP5, and LP6, respectively) for 15-42 d of age. The results showed that dietary treatment significantly affected feed conversion ratio (FCR) ( P < 0.05), but no linear or quadratic trends were observed ( P > 0.05); blood urea nitrogen (BUN) content in the grower phase changed significantly ( P < 0.05); abdominal fat yield (AFY) increased linearly ( P = 0.002); meat color parameters (lightness [L*], redness [a*], and yellowness [b*]) were significantly altered, showing both linear and quadratic trends ( P < 0.05); and among meat quality traits, only shear force was significantly affected, also displaying linear and quadratic trends ( P < 0.05). The LP diet improved the structure of the intestinal microbiota and significantly reduced nitrogen excretion ( P < 0.05). In conclusion, reducing the dietary CP level by 2 percentage points was the optimal strategy, as it maintained growth performance while reducing nitrogen pollution, provided theoretical basis and practical guidance for the design of LP diet in the poultry industry, and contributed to the goal of cost reduction and efficiency improvement in China’s livestock and poultry production.