A bacteriophage cocktail delivered in feed significantly reduced <i>Salmonella</i> colonization in challenged broiler chickens

Nontyphoidal <i>Salmonella</i> spp. are a leading cause of human gastrointestinal infections and are commonly transmitted via the consumption of contaminated meat. To limit the spread of <i>Salmonella</i> and other food-borne pathogens in the food chain, bacteriophage (phage) therapy could be used during rearing or pre-harvest stages of animal production. This study was conducted to determine if a phage cocktail delivered in feed is capable of reducing <i>Salmonella</i> colonization in experimentally challenged chickens and to determine the optimal phage dose. A total of 672 broilers were divided into six treatment groups T1 (no phage diet and unchallenged); T2 (phage diet 10⁶ PFU/day); T3 (challenged group); T4 (phage diet 10⁵ PFU/day and challenged); T5 (phage diet 10⁶ PFU/day and challenged); and T6 (phage diet 10⁷ PFU/day and challenged). The liquid phage cocktail was added to mash diet with <i>ad libitum</i> access available throughout the study. By day 42 (the concluding day of the study), no <i>Salmonella</i> was detected in faecal samples collected from group T4. <i>Salmonella</i> was isolated from a small number of pens in groups T5 (3/16) and T6 (2/16) at ∼4 × 10² CFU/g. In comparison, <i>Salmonella</i> was isolated from 7/16 pens in T3 at ∼3 × 10⁴ CFU/g. Phage treatment at all three doses had a positive impact on growth performance in challenged birds with increased weight gains in comparison to challenged birds with no phage diet. We showed delivering phages via feed was effective at reducing <i>Salmonella</i> colonization in chickens and our study highlights phages offer a promising tool to target bacterial infections in poultry.