Research On The Development Of Substitute Antibiotics For Bullfrog(Rana Catesbiana) Based On Acacia Mangium Tannin

Acacia mangium tannin(AM),a kind of plant tannin that are easy to extract,can be used as a green additive to replace antibiotics,which has potential application value in aquaculture industry.However,the mechanism of the AM in bullfrog is not clear.In order to deal with high prevalence of bullfrog in high density culture,the bullfrog was selected as the research topic.Firstly,According to the bacteriostatic effect of plant tannins and acidifiers,the best acacia tannins and formic acid were selected as preliminary additives to replace antibiotics.A 40-day breeding experiment was conducted to determine the qualitative and quantitative additives of Acacia mangium tannin.The survival growth,histological structure,digestive enzyme activities,immune response,antioxidant indices and intestinal microflora of experimental groups were compared to explore a new type of feed additive based on Acacia mangium tannin as an alternative for the antibiotics.The effects of AM addition on non-specific immunity and aeromonas hydrophila ability of bullfrog were further studied according to the aeromonas hydrophila infection test.The main results and conclusions are as follows:1.Screening for bacteriostatic effects of plant tannins and acidifiersAt 0.4g/L AM level and 0.25g/L FA level,the growth inhibition rates of microbial colonies in the bullfrog breeding pond were 40.68% and 49.13%,respectively,which were significantly higher than other supplemental levels(19%～30%)(P < 0.05).Therefore,the inhibitory effect of aeromonas hydrophila on the growth of single pathogenic bacteria was basically the same as that of the water microbial colony of bullfrog breeding pond.2.Effects of Acacia mangium tannin(AM)and formic acid(FA)on growth performance,immune capacity,antioxidant capacity and intestinal microflora of bullfrog1)Dietary AM,AM and FA addition can improve the weight gain rate and the survival rate of bullfrog under harsh breeding conditions,while acacia mangium tannin alone exhibits better effect.2)Dietary AM,AM and FA can improve the activities of alkaline phosphatase,immunoglobulin and lysozyme,while inhibits the activities of trough alanine aminotransferase and aspartate aminotransferase in serum of bullfrog.At the same time,the activities of antioxidant enzymes(SOD,T-AOC,GSH,CAT)in bullfrog liver were enhanced,thus the liver health was protected,while acacia mangium tannin alone exhibits better effect.3)The expressions of pro-inflammatory factors(tnf-α,il-1β)in liver and spleen of bullfrog were significantly decreased by dietary AM,AM and FA.4)Dietary AM,AM and FA greatly can change the composition of intestinal microflora,reduce the abundance of potential pathogenic bacteria,and protect the normal intestinal function.3.Effects of Different levels of Acacia mangium tannin(AM)on growth performance,immune capacity and antioxidant capacity of bullfrog1)The weight gain rate and survival rate of bullfrog under normal culture condition were improved by adding low and medium concentration of AM,which will be better at an AM level of 8g/kg.2)The activities of serum immunoglobulin G and immunoglobulin M were increased by adding low and medium concentration of Acacia macanum in the diet,while the activities of down-trough pyruvic transaminase and aspartate oxalacetic transaminase in bullfrog were decreased.At the same time,the activities of antioxidant enzymes(SOD,T-AOC,GSH,CAT)in bullfrog liver were enhanced,and the liver health was protected,especially better at 8g/L.3)The expression of pro-inflammatory factors(tnf-α,il-1β)in liver and spleen of bullfrog were significantly decreased by adding low and medium concentration of AM in the diet.(P < 0.05)4.Effects of Acacia mangium tannin(AM)on resistance to pathogen infection of bullfrog1)After 7 days of aeromonas hydrophila infection,the bullfrogs in each group died,especially the common diet group,which showed the highest cumulative mortality.However,the cumulative mortality decreased significantly after adding antibiotics and 8g/kg AM in the diet.2)After 7 days of aeromonas hydrophila infection,the supplementation of antibiotics and 8g/kg AM could significantly regulate the expression levels of pro-inflammatory factors(il-1β,il-17,tnf-α)in liver and spleen,promote the health of immune tissue and improve the immune capacity of bullfrog.In conclusion,the results of this study indicate that a green and environmentally friendly bullfrog feed additive based on Acacia mangium tannin has been developed.The growth performance,antioxidant and disease resistance of bullfrog were significantly improved by adding appropriate amount of Acacia mangium tannin in the diet.To reduce the incidence of disease of bullfrog in harsh breeding environment,and preliminarily elucidate the antibacterial mechanism of Acacia macanum tannin.It provides an important basis for solving the problem of overuse of antibiotics and promoting the healthy and sustainable development of aquaculture industry.The innovation of this study lies in that it is the first time to study the antibacterial mechanism of plant tannins in cultured bullfrogs,and it is the first time to reveal that plant tannins can enhance non-specific immunity of bullfrogs.