| The long-term and extensive use of antibiotics in the current aquaculture has caused a series of problems.Therefore,it is an inevitable development trend to develop efficient new green feed additives for preventing diseases.In this study,the cultivation conditions of the astragalus fermented using Bacillus subtilis and lactic acid bacteria were optimized first to obtain the best culture conditions for fermentation;then different doses of fermented astragalus preparations were added to the hybrid sturgeon bait to study its application effect on the growth and survival rate of hybrid sturgeon,and the Hematology indicators of hybrid sturgeon were measured the safety of fermented astragalus preparations was checked.The main results are as follows:The optimum fermentation conditions for astragalus fermented by Bacillus subtilis and lactic acid bacteria are as follows:astragalus,soybean meal,brown sugar and wheat bran are used as fermentation medium;water content is 70%;sterilization by ultraviolet light;According to the inoculum volume of 2%,inoculate at a final concentration of 1×10~6CFU/m L;Bacillus subtilis was first fermented for 48 h and then inoculated with lactic acid bacteria;the fermentation temperature was 32°C;the loading capacity was 3000 g.Under these conditions,the number of Bacillus subtilis and lactic acid bacteria in the fermented astragalus products reached the highest levels,reaching 2.6×10~9CFU/g and 7.9×10~8CFU/g,respectively.The preparation of astragalus fermented,probiotics,astragalus and other groups had no significant effect on the growth performance of hybrid sturgeon.Each experimental group was challenged with streptococcus,and the results were as follows:the survival rate of the probiotic group,the astragalus group and the control group was not significantly different(P>0.05);the survival rate of the vaccine group was significantly higher than that of the control group(P<0.05);all fermented astragalus The survival rates of the groups were higher than those of the control group,and the differences between the 5‰and 10‰fermented astragalus groups were significantly different from those of the control group(P<0.05).It shows that both fermented astragalus and vaccine can significantly improve the survival rate of hybrid sturgeon.Feeding hybrid sturgeon with 5‰～10‰of fermented astragalus can significantly improve the ability of hybrid sturgeon to resist Streptococcus infection.The content of each index in the blood serum of hybrid sturgeon changed with the addition of fermented astragalus in the feed and the breeding time.On the 14th day,the CAT content of the 10‰fermented astragalus group was significantly higher than that of the control group(P<0.05);on the 21st day,the LZM content of the 5‰fermented astragalus group was significantly higher than that of the control group(P<0.05).The ACP content of the astragalus group was significantly higher than that of the control group(P<0.05).In addition,the content of LZM gradually increased with time,and then showed a steady downward trend;the content of ACP,AKP,Cr,and TP all increased gradually with time;the content of CAT increased steadily with time and then decreased rapidly;the content of SOD in each group showed a wave-like change with time;T-AOC content decreased steadily with time and then increased.Comprehensive comparison of the levels of LZM,ACP,AKP,CAT,SOD,T-AOC,Cr,and TP in the control group and each experimental group,combined with the results of the challenge test,adding 10‰of fermented astragalus to the feed can improve the non-specific immunity of hybrid sturgeon Features.The viable counts of Bacillus subtilis and Lactobacillus in the fermented astragalus preparations gradually decreased with time,and no adverse reactions were found when the fermented astragalus preparations were applied to hybrid sturgeon. |
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