Effects of dietary supplementation of duo-strain probiotics with post-spraying technology on growth performance, digestive enzyme, antioxidant capacity and intestinal microbiota of grass carp (Ctenopharyngodon idella)

The aim of the present experiment was to study the effects of duo-strain probiotics (DSP, Bacillus subtilis and Lactobacillus plantarum) culture supplemented by post-spraying technology on the growth performance, digestive enzyme activity, antioxidant capacity and intestinal microbiota of grass carp, as well as the viability of the DSP in the post-spraying and storage process. In the present experiment, 900 of Grass carp (41.4 ± 1.8 g) were fed with a basal diet (control group) and the DSP diet containing 105 CFU/g (T1 group) or 106 CFU/g (T2 group) probiotics supplemented by the post-spraying technology in 9 cages for 6 weeks. Meanwhile, the amount of DSP in the diets was monitored for 30 days. The results revealed that the viability of the B. subtilis and L. plantarum was 98.14% and 98.09% after the post-spraying and there were no significant differences among 30 days of storage in comparison with final viability of 99.13% and 99.10%. The result of the feed experiment indicated that the diet supplemented DSP significantly increased the percent weight gain (PWG), specific growth rate (SGR) and survival rate (SR) of grass carp, and decreased the feed conversion ratio (FCR) (P < 0.05). Additionally, the digestive enzyme activity (total protease, α-amylase, lipase and trypsin) and antioxidant capacity (superoxide dismutase, malondialdehyde and catalase) were significantly improved in the DSP groups than those in the control (P < 0.05). Furthermore, in comparison with the control group, the relative abundance of Bacteroidetes and Firmicutes was significantly increased (P < 0.05), and Proteobacteria and Cyanobacteria were significantly decreased (P < 0.05). Overall, these results in the present experiment demonstrated that post-spraying technology could be a potential way for probiotics supplementation in the aquatic feedstuff process and the beneficial effects of DSP on grass carp.