Improving health and productivity in laying hens with the phage cocktail SalmoFree®.

Avian salmonellosis, caused by Salmonella enterica sub. enterica serovar Gallinarum, represents a substantial threat to poultry production in Latin America. This study assessed the efficacy of the phage cocktail SalmoFree®, which comprises six lytic bacteriophages, in preventing avian salmonellosis in two commercial laying hen farms in Colombia. A total of 95,491 hens were observed over two production cycles under field conditions. The study involved baseline assessments followed by the preventive administration of SalmoFree® via drinking water at regular intervals. Effectiveness was evaluated through microbiological, histopathological, and serological analyses, alongside monitoring of zootechnical parameters and genomic characterization of bacterial isolates. S. Gallinarum was sporadically isolated during the trial; however, in barns where phages were administered, mortality was controlled without antibiotics, in contrast to baseline barns where antibiotics were necessary. Histopathological findings confirmed tissue lesions consistent with salmonellosis, particularly in baseline groups. Zootechnical evaluations indicated that phage administration was associated with reduced mortality and enhanced egg production, with statistically significant improvements observed in one of the farms. Genomic analysis of S. Gallinarum confirmed all isolates as ST78, possessing multiple virulence genes and mutations associated with ciprofloxacin resistance. Escherichia coli isolates exhibited high genomic diversity and multidrug resistance profiles; these isolates were also evaluated to determine whether phage use against Salmonella affected the resistance profile of other bacteria present in the birds. However, no correlation was found between phage administration and resistance gene abundance or MIC values in Salmonella and E. coli isolates. These findings demonstrate the preventive potential of SalmoFree® against avian salmonellosis under commercial conditions and support its role as a complementary tool for antimicrobial-free disease control in poultry production.