Evaluation of Bacteriophage vB_SalS_KY05 Lysate on Physiological Status, Egg Production, and Intestinal Microbiota in Laying Hens

Bacteriophage vB_SalS_KY05 (KY05) was propagated using a non-pathogenic E. coli K-12 strain. The lysate was administered via water for 56 days. Thirty Lohmann Brown-Classic laying hens (53 weeks old) were randomly assigned to three groups: the Control group (without phage lysate), the Low-Phage group (105 PFU/mL) and the High-Phage group (108 PFU/mL). This study aimed to evaluate the safety profile of the administered KY05 lysate by assessing its endotoxin content and its effects on immune responses and gut microbiota in laying hens. Phage lysate did not adversely affect physiological status, laying performance, plasma biochemical parameters, intestinal morphology, or inflammatory cytokine concentrations when compared with the results for the Control group, supporting the physiological safety of KY05 lysate in laying hens. Fecal Lactobacillus counts were not affected, while fecal E. coli counts showed a slight, although not statistically significant, decrease in the phage-treated groups. In cecal 16S rRNA analysis, microbial composition did not differ significantly among treatments. These findings support the safety of prolonged KY05 lysate administration under the experimental conditions used in this study and warrant further evaluation under field conditions.