In ovo phage administration to mitigate Salmonella Typhimurium colonization in broiler chickens – A new firewall strategy for the poultry industry

Hatcheries, as the initial stage of the poultry production pipeline, play a pivotal role in the potential spread of Salmonella . The high-density rearing conditions of industrial poultry production, coupled with the routine transfer of chicks from hatcheries to multiple farm locations, heighten the likelihood of pathogen dissemination across wide geographic areas. Therefore, there is a need for innovative disinfection strategies that align with regulatory requirements and effectively target pathogenic threats. In this context, this study aimed to assess the safety and efficacy of bacteriophages application in ovo as a preventive measure to mitigate Salmonella transmission from hatcheries to the rearing farms. To do so, two experiments were conducted. Experiment 1 evaluated the safest and most effective in ovo inoculation site for phage delivery, while the Experiment 2 tested the efficacy of a phage cocktail administered via the amniotic liquid in reducing Salmonella Typhimurium colonization during the first 21 days post-hatch after direct and indirect exposure. The results demonstrated that phage administration in the amniotic liquid was the safest and most suitable in ovo inoculation site. Furthermore, phage treatment significantly reduced Salmonella colonization in directly infected chicks and completely prevented transmission in indirectly exposed birds. In ovo administration of the phages proved to be a promising prophylactic firewall strategy to limit the spread of Salmonella within the production chain. Created (Created in https://BioRender.com ). • In ovo administration of bacteriophages is safe for chicken embryos. • In ovo phage administration reduced Salmonella colonization during the rearing cycle. • In ovo administration of phages impeded horizontal transmission of Salmonella.