Effects of live and heat-killed Limosilactobacillus ingluviei C37 on broiler performance, gut health, and bacterial cell wall characterization using Fourier Transform Infrared spectroscopy

This study investigated the efficacy of Limosilactobacillus ingluviei C37 (LIC37) in live and heat-killed forms on growth performance, carcass characteristics, cecal microbial populations, short-chain fatty acids (SCFAs), and ammonia production in broiler chickens from 1 to 42 days of age. Fourier Transform Infrared spectroscopy (FTIR) was used to characterize protein structural differences between both LIC37 forms. A total of 240 one-day-old male Cobb 500 chicks were assigned to four dietary treatments in a completely randomized design (CRD) with six replicates of ten chicks each: 1) basal diet (control), 2) basal diet + 50 mg/kg zinc bacitracin (positive control), 3) basal diet + 1 × 10⁸ CFU/kg live LIC37, and 4) basal diet + 1 × 10⁸ CFU/kg heat-killed LIC37. Live and heat-killed LIC37 significantly increased body weight gain compared to the control (P < 0.001), with performance comparable to the positive control (P > 0.05). Both LIC37 forms enhanced serum lysozyme activity and reduced meat cholesterol compared to the control and positive control groups (P < 0.05). Feed conversion ratio, survival rate, and meat quality parameters were unaffected by treatments. In addition, LIC37 supplementation increased cecal microbial beneficial bacteria (Lactobacillus and Bifidobacterium), decreased pathogenic bacteria (Enterobacter and E. coli), elevated SCFAs production, and reduced ammonia levels. FTIR analysis revealed that heat-killed LIC37 exhibited substantially altered protein secondary structures, particularly reduced α-helix content, while β-sheet structures remained relatively stable compared to live cells. These findings demonstrate that LIC37 supplementation, regardless of cell viability, effectively improves growth performance and gut health in broilers, suggesting its potential as a feed additive in poultry production.