2.4. Sample Collection and Treatment

After 35 d of experimental intervention, three chickens were randomly selected from each replicate. Blood samples were collected from wing veins, and then the birds were sacrificed by cervical dislocation. Cecal contents and cloacal samples were aseptically collected from each bird. Blood samples were allowed to clot at room temperature before centrifugation at 4000× g for 10 min for serum collection. Samples were immediately placed in an ice box and then stored at −80 °C for subsequent index measurements. Blood serum samples were assessed for 9 blood biochemistry parameters at the Guangdong Animal Experiment Center (Guangzhou, China), and the cecum contents were sent to Shanghai Ling’en Biotechnology Co., Ltd. (Shanghai, China) for PacBio sequencing.