Effect of bacteriophages on growth performance and health indicators in broiler chickens in the absence of bacterial challenge - A review

This review examines bacteriophages asalternatives toantibiotic growth promoters (AGPs) inbroiler chickens, with aunique focus oneffects observed instudies without experimental bacterial challenges. Driven byglobal antimicrobial resistance (AMR) concerns and sustainable poultry production demands, phage supplementation, atargeted strategy, potentially improves growth performance and gut health bypreserving beneficial microbiota. This literature analysis assesses phage efficacy inhealthy broilers under non-challenge conditions, evaluating key variables such asphage concentration, delivery, and targets, aswell asoutcomes such asfeed conversion ratio (FCR) and gut health markers. Crucially, this review extends beyond efficacy toexplore phage immunomodulatory capabilities, outlines optimisation strategies, and addresses risks and mitigation. Key findings show mixed efficacy ofphages innon-challenged broilers: significant improvements inFCR and gut health were generally observed with high phage concentrations (e.g., ≥108PFU/g) and continuous delivery protocols, whereas lower doses yielded inconsistent orminimal benefits. Furthermore, choosing which bacteria phages target – for example, aiming atpathogens like Salmonella ormanaging common gut bacteria such asE.coli – greatly impacts outcomes. While phages show considerable potential as AGP alternatives, the review highlights that further research is vital to resolve inconsistencies, standardise protocols, and understand host genetic and environmental influences to optimise their commercial application.