Comparative effects of multi-strain Yeast, bacterial, and yeast–bacterial preparations on growth, antioxidant status, gene expression, meat quality, and cecal microbiota in broiler chickens

This study evaluated the effects of dietary supplementation with live yeast and bacterial culture preparations on growth performance, carcass and meat quality, blood biochemical indices, antioxidant-related gene expression, and cecal microbiota in Arbor Acres broilers. A total of 336 one-day-old broilers were randomly assigned to 4 groups (n = 84/group) and fed a basal diet (F1, control) or the basal diet supplemented with 2 mL/kg of a 3-strain yeast preparation (F2), 2 mL/kg of a 4-strain bacterial preparation (F3), or 1 + 1 mL/kg of a combined yeast-bacterial preparation (F4). The experiment lasted 31 d. Dietary supplementation improved overall growth performance compared with the control (P < 0.05), with F2 producing the highest final body weight, weight gain, and production index, whereas F3 showed favorable feed utilization. F3 also produced the greatest modulation of cecal microbiota, characterized by increased Lactobacillus and decreased E. coli, total bacterial count, and Pseudomonas. Hepatic SOD1 and CAT1 expression and GPx and GST activities increased, whereas MDA decreased in F3 (P < 0.05). Serum ALT, AST, urea, creatinine, cholesterol, triglycerides, and LDL decreased, whereas HDL, IgG, IgM, and total protein increased, with the most pronounced responses generally observed in F3. Carcass yield and relative breast yield were highest in F2 and F4, whereas F4 reduced meat pH without adversely affecting other measured meat-quality traits. Overall, the responses differed among preparations, with the yeast preparation primarily supporting growth performance and the bacterial preparation producing broader antioxidant, metabolic, immune, and microbiota-related responses.