Abstract: The purpose of this study was to explore the effects of cocktail composed of four pathogenic phages on growth performance, blood routine, serum biochemical index, antioxidant capacity, inflammatory cytokines, immunoglobulin and fecal microbiota of weaned piglets, so as to evaluate the safety of preparation of phage in vivo. Twelve healthy 21-day old weaned piglets with similar body weight were randomly divided into control group (CON) and phage group (Phage) with 6 piglets per group. The phage group was given 10 mL phage cocktail by gavage for 20 consecutive days (the total amount of each phage was 5×10⁸ PFU), and the control group was gavaged equal volume of SM buffer. Blood and stool samples were collected at day 11 and 21. The results showed that:1) there was no significant difference in growth performance between the two groups. 2) There was no significant difference in blood routine indexes between the two groups on the 11th and 21th day (P>0.05). The albumin content in serum biochemical indexes of piglets in phage group increased significantly on the 11th day (P<0.05), but returned to the level of control group on the 21th day. No significant difference was present in other serum biochemical indexes between the two groups on the 11th and 21th day (P>0.05). 3) Compared with the control group, the enzymatic activity of CAT in serum of piglets in phage group had an upward trend (P=0.066), and no significant difference was found in other antioxidant indexes between the two groups (P>0.05). 4) At day 11, the serum IFN-γ, TNF-α and IL-1β levels of the piglets in the phage group were significantly increased, (P<0.05), and the IL-10 level was significantly decreased (P<0.05). At day 21, the levels of IFN-γ, TNF-α, IL-17 and TGF-β in the phage group were significantly increased (P<0.05), and the IL-4 and IL-10 were significantly decreased (P<0.05). 5) Compared with the control group, the levels of IgA, IgG and IgM in serum of piglets in phage group at 21 days were significantly increased (P<0.01). 6) There was no significant difference in α diversity indexes of fecal microbiota between the two groups at day 11 (P>0.05). On day 21, compared with the control group, the Shannon index in phage group was significantly increased (P<0.05). β-diversity analysis showed no significant difference in microbial community composition between the two groups at day11 and 21. The results of differential flora analysis showed that there were no bacterial families and genera with significant differences in relative abundance between the two groups on the 11th day, while on the 21th day, compared with the control group, the relative abundance of Oscillospiraceae in the phage group was significant increased (P<0.05), and this difference at the genus level was manifested as a significant increase in the relative abundance of Ruminococcus_gauvreauii_group (P<0.05). In conclusion, continuous gavage of the phage cocktail for 20 days had no significant effect on the growth performance and routine blood parameters of piglets; It has a positive effect on antioxidant function and significantly improves the α diversity of bacterial community. At the same time, the serum levels of proinflammatory cytokines and immunoglobulin were significantly increased.

Key words: phage cocktail, inflammatory cytokines, immunoglobulin, fecal microbiota, serum biochemical index, blood routine, antioxidant capacity