Systemic effects of a phage cocktail on healthy weaned piglets

Nowadays, it is urgent to search antibiotic alternatives. Bacteriophages (phages) are viruses spe-cifically infecting bacteria and were considered as a prospective substitute of antibiotics. Nu-merous studies have demonstrated that phages can effectively treat intestinal bacterial infections. However, research on the impact of phages on overall body health once they enter the intestine is limited. In this study, we utilized weaned piglets as subjects to evaluate the systemic effects of an orally administered phage cocktail on their health. We found phages did not affect the piglets' growth performance, serum biochemical indices, or most organ indices, but negatively affected their antioxidant system. Phages increased the pH of jejunum, but did not influence the activities of digestive enzymes. Interestingly, it enhanced intestinal barrier function and altered the intes-tinal microbiota structure. Phages also altered the host immune status of piglets, inducing a sig-nificant increase in some pro-inflammatory factors, but the count of most immune cells in the blood did not change, except for an increase of basophil. This study indicates that the impact of phages on body health is complex, especially regarding immune status. Our study is informative and further improves the implementation and supervision of phage therapy.