Abstract: 【Objective】 This study aims to investigate the effects of supplementation of Bacillus subtilis spores in the feed and addition of photosynthetic bacteria (PSB) on living water and laying performance of laying ducks and their mechanisms.【Method】A total of 240 laying ducks were randomly and equally allocated into 24 “slate floor bed + water pool” individual pens using a 2×2 factorial design with 6 replications per treatment. After 7-d pre-feeding, the ducks were received 2 main treatments: supplementation of Bacillus subtilis (viable count 8 × 10⁷ cfu/kg) in the feed, and addition of PSB (viable count 1.8 × 10¹² cfu/kg) to the living water. Neither supplementation of B. subtilis nor addition of PSB into living water was used as the control group (C group), supplementation of B. subtilis was used as the B. subtilis group (B group), addition of PSB into living water was used as the PSB group (P group), and both supplementation of B. subtilis and addition of PSB into living water was used as the combined group (BP group). In the 120-d experimental period, the average laying rate, average feed intake and average feed to egg ratio were calculated every10 days. The living water samples were collected every 10 days for measuring counts of E. coli and Salmonella + Shigella. The living water and blood samples were collected every 15 days for measuring LPS concentration. At the end of the experiment, the fresh feces were collected for measuring counts of E. coli and Salmonella + Shigella. The mucosa and tissues of duodenum, jejunum and ileum were collected for measuring LPS concentrations and mRNA expression of inflammation/apoptosis - related genes, respectively. During the experiment, the animals were maintained under natural photoperiod. Living water and feed were available to the ducks ad libitum. The linear mixed model of SPSS, for the analysis of repeated measurements, was used with comparisons using the LSD correction. The data with repeated measurements included LPS concentrations in living water and plasma, feed intake, laying rate, feed to egg ratio, and counts of E. coli and Salmonella + Shigella in living water. The one-way ANOVA was used for data including counts of E. coli and Salmonella + Shigella in feces, LPS concentrations of intestinal mucosa, and tissue gene expression. Post-hoc differences between treatment groups were further examined using Duncan test.【Result】Both Bacillus subtilis and PSB treatments did not significantly affect feed intake (P＞0.05), Caspase-3 and Bcl-2 mRNA expression in jejunum (P＞0.05), Bcl-2 mRNA expression in ileum (P＞0.05), and IL-1β mRNA expression in spleen, however, they significantly increased laying rate (P＜0.001), and decreased feed to egg ratio (P＜0.001), LPS concentrations of living water (P＜0.001), duodenum (P＜0.01) and ileum (P＜0.01), counts of E. coli in feces (P＜0.001), and mRNA expression of TLR4 in jejunum (P＜0.05) and Caspase-3 in ileum (P＜0.05). There was significant effect of time on feed intake, laying rate, feed to egg ratio, LPS concentration and counts of E. coli and Salmonella + Shigella in living water (P＜0.01). Compared with B and BP groups, LPS concentration in plasma and counts of Salmonella + Shigella in feces in C and P groups were increased (P＜0.05), and LPS concentration in jejunum, counts of Salmonella + Shigella in living water and TNF-α mRNA expression in spleen were also increased (P＜0.05). The count of E. coli in living water in BP group was lower than in C, B and P groups (P＜0.05). Only in BP group was TLR4 mRNA expression in ileum lower (P＜0.05), and IL-10 mRNA expression higher than in C group (P＜0.05).【Conclusion】The results indicate that B. subtilis and PSB treatments improved laying performance of laying ducks by decreasing the counts of Gram-negative bacteria and level of LPS in cultivated water, and decreasing the level of LPS in intestinal mucosa and plasma and inflammatory response.

Key words: laying ducks, laying performance, photosynthetic, bacillus, lipopolysaccharide