Modulating cecal microbiota and systemic physiology in broilers through non-antibiotic dietary approaches

This study evaluated the effects of lactic acid (LAC) and spirulina (SPR) on growth performance, carcass traits, blood parameters, antioxidant status, and cecal microbiota of broiler chickens as natural antioxidant and growth-promoting agents. A total of 360 one-day-old Ross 308 chicks were randomly assigned to six groups in a completely randomized design. Each group consisted of six replicates with ten unsexed chicks per replicate. The dietary treatments were as follows: NC (control, basal diet), PC (0.5 g polymyxin E antibiotic/kg diet), LAC 2 (2 g LAC/kg diet), LAC 4 (4 g LAC/kg diet), SPR 1 (1 g SPR/kg diet), and SPR 2 (2 g SPR/kg diet). No significant differences (P > 0.05) were observed among treatments for live body weight (LBW), feed intake (FI), feed conversion ratio (FCR), or performance index (PI), except for FI during days 1–21, where the SPR 1 group showed improved FCR. Carcass characteristics did not differ significantly among treatments. LAC and SPR supplementation (P < 0.001) reduced total protein and albumin levels compared with NC and PC groups. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, as well as urea and creatinine levels, were lower in the LAC 4 and SPR 2 groups. Spirulina supplementation at different levels increased glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities, along with glutathione (GSH) and malondialdehyde (MDA) concentrations, compared with NC, PC, and LAC treatments. Significant (P < 0.05) differences in total bacterial count (TBC) were recorded, with the NC group showing the highest values. Lactobacilli and E. coli counts were highest in the LAC 2 and LAC 4 groups, whereas SPR 1 had the greatest Salmonella counts. In conclusion, dietary inclusion of 2 g LAC/kg improved gut health by promoting microbial balance, while 1 g SPR/kg enhanced antioxidant status and organ function, thereby improving overall physiological resilience in broilers.