Effect of in ovo and oral bacteriophage administration on intestinal Salmonella colonization in Cobb broiler chicks.

Salmonellosis is a major zoonotic disease of poultry that causes substantial economic losses and poses a significant public health risk. Given the growing concern of antimicrobial resistance, this study evaluated the efficacy of lytic bacteriophages against Salmonella enterica serovar Typhimurium in Cobb broiler chicks following in ovo and oral administration. Bacteriophages isolated and maintained in the Department of Veterinary Microbiology, DUVASU, Mathura, were characterized by transmission electron microscopy, demonstrated a broad host range against multiple Salmonella serovars, and showed no lytic activity against non-target bacterial species. The in vivo efficacy of the phages was assessed in 60 broiler chicks allocated to six groups (n=10): oral administration at multiplicity of infection (MOI) 1 and MOI 2, in ovo administration at MOI 1 and MOI 2, challenged control, and unchallenged control. Phage treatment significantly reduced fecal shedding of S. Typhimurium compared with the challenged control group throughout the experimental period. Oral administration at MOI 1 resulted in the greatest reduction in bacterial shedding, while in ovo administration at MOI 2 provided sustained suppression of bacterial colonization. Cecal bacterial counts were significantly lower in all phage-treated groups, with the most pronounced reductions observed at MOI 1. Histopathological examination further demonstrated reduced intestinal lesions and tissue damage in phage-treated birds compared with challenged controls. These findings demonstrate that lytic bacteriophages effectively reduce intestinal colonization and fecal shedding of S. Typhimurium in broiler chickens and highlight their potential as a promising alternative to antibiotics for the control of poultry salmonellosis.