Effects of Dietary Metabolizable Energy and Crude Protein Levels on the Apparent Nutrient Metabolism, Gastrointestinal Development, and Microbial Composition in Jingyuan Chicken

The effects of varying dietary metabolizable energy (ME) and crude protein (CP) levels, along with their interactive effects, on the apparent nutrient metabolism, development of digestive organs, intestinal morphology, and microbial composition in Jingyuan chickens during the growing phase were evaluated. A total of 540 seven-week-old male Jingyuan chickens were randomly assigned to 9 groups, with 6 replicates per group and 10 chickens per replicate. The trial lasted for 11 weeks. A 3×3 factorial design was adopted, comprising three levels of ME, namely, low (11.28 MJ/kg, LE group), medium (11.70 MJ/kg, ME group), and high (12.12 MJ/kg, HE group) and three levels of CP, namely, low (14.00%, LP group), medium (15.50%, MP group), and high (17.00%, HP group). The levels of ME and CP, along with their interactions, had a significant effect on the average daily gain (ADG), average daily feed intake, feed-to-gain ratio (F/G), apparent metabolizable rate of CP, gizzard weight, duodenal and cecal lengths, jejunal villus height (VH), crypt depth (CD), and muscle layer thickness (MLT) (P<0.05). The combination of mediumlevel ME (11.70 MJ/kg) and medium-level CP (15.50%) (MEMP group) exhibited the best performance and exhibited the highest ADG and the lowest F/G (P <0.05). Moreover, this group exhibited significantly higher apparent metabolizable rates of CP, gizzard weight, duodenal length, jejunal VH, CD, and MLT compared with those in the other groups (P <0.05). Dietary ME and CP levels significantly influenced cecal microbial composition. Chickens in the MEMP group exhibited an increased abundance of Erysipelotrichaceae, Syntrophomonadaceae, Akkermansia, and Clostridia_vadinBB60_group, and significantly decreased the relative abundance of Desulfobacterota (P <0.05). This study demonstrated that dietary ME and CP levels, along with their interactions, could significantly influence the growth performance, apparent nutrient metabolism, and intestinal development of Jingyuan chickens during the growing phase. Dietary ME and CP levels modulated the cecal microbiota composition, potentially inhibiting the abundance of harmful bacteria Desulfobacterota while enriching the abundance of beneficial bacteria, thereby enhancing gut development and nutrient absorption. The combination of medium-level ME and CP (11.70 MJ/kg ME, 15.50% CP) demonstrated the most favorable outcomes in our study.