Effects of dietary energy and protein levels during brooding on performance, blood parameters, metabolome and gut microbiota in native chickens

The nutrient requirements of slow-growing native chickens during the critical brooding period are not well-defined, hindering the development of precision feeding strategies. This study aimed to systematically evaluate the effects of dietary metabolizable energy (ME) and crude protein (CP) levels on growth performance, systemic metabolism, and gut health in Danzhou chickens during the brooding phase (1-35 days). A total of 540 one-day-old female Danzhou chicks were allocated to nine diets in a 3 × 3 factorial arrangement, with three ME levels (11.50, 12.10, 12.70 MJ/kg) and three CP levels (18%, 19%, 20%). Growth performance, serum parameters, intestinal morphology, cecal microbiota, and tissue metabolomes were comprehensively assessed. The results revealed that dietary ME level exerted a more profound effect than CP on most parameters. The diet containing 12.10 MJ/kg ME and 20% CP yielded the best overall growth performance, with the highest final body weight (BW) and average daily gain (ADG), and the lowest feed-to-gain ratio (F/G). Serum leptin and IGF-1 concentrations were elevated with medium and high ME levels, indicating enhanced anabolic signaling. The 12.70 MJ/kg ME diet modified the cecal microbiota by increasing the Firmicutes-to-Bacteroidota ratio. Metabolomic analysis revealed that the 12.70 MJ/kg of ME and 20% of CP diet significantly enriched the biosynthesis pathway of unsaturated fatty acids in breast muscle, increasing linoleic and α-linolenic acid levels. In conclusion, for optimal growth performance during brooding, a 12.10 MJ/kg ME and 20% CP diet is recommended for Danzhou chickens. Alternatively, a 12.70 MJ/kg ME and 20% CP diet can be utilized to enhance the fatty acid profile of meat, offering flexible nutritional strategies for different production goals.