Effects of Different Rearing Systems (Cage vs. Free-Range) on Growth Performance, Serum Biochemical Parameters, Slaughter Performance, Cecal Microbiota, and Hepatic Metabolism of Yellow-Feathered Broilers

This experiment investigated the effects of two rearing systems, cage and free-range, on growth performance, serum biochemical parameters, slaughter performance, cecal microbiota, and hepatic metabolism of yellow-feathered broilers. A total of 240 healthy 21-day-old Liangfenghua yellow-feathered male broilers with similar body weight were randomly assigned to a cage group (LY) and a free-range group (SY), with 10 replicates per group and 12 birds per replicate. All birds were fed the same diet until 63 days of age. Compared with the LY group, the SY group had significantly lower final body weight, average daily gain, and abdominal fat percentage (p < 0.05), while average daily feed intake and feed-to-gain-ratio were significantly higher (p < 0.05). The Shannon and Simpson indices of the cecal microbiota were significantly higher in the SY group (p < 0.05), and the genera Bacteroides, Lactobacillus, Rikenella, and Oscillibacter were specifically enriched. A total of 560 differential metabolites were identified by liver non-targeted metabolomics, and these metabolites were significantly enriched in the necroptosis, cysteine and methionine metabolism, thiamine metabolism, and amino sugar and nucleotide sugar metabolism pathways (p < 0.05). Correlation analysis between cecal microbiota and liver metabolites revealed that the differentially abundant bacterial genera showed significant negative correlations with multiple amino acid metabolites in the liver. In conclusion, the free-range rearing system reduced the growth performance of yellow-feathered broilers but enriched specific bacterial genera, increased gut microbiota diversity, and modulated host amino acid metabolism and energy homeostasis through the “gut microbiota–liver” axis, ultimately inducing an adaptive metabolic state characterized by reduced abdominal fat deposition and remodeling of hepatic metabolic pathways.