| Litopenaeus vannamei were supplied with 0%,1%,3% and 5% poly-β-hydroxybutyrate(PHB)in artificial compound feed for 35 days,and their growth performance,body composition,intestine short-chain fatty acids(SCFA)content,immune and digestive function and composition of intestine microbiota were compared in order to explore the improvement effect of PHB on growth performance and intestine health of L.vannamei.The results are as follows: 1 Effects of PHB on growth performance and body composition of L.vannameiThe effect of PHB on growth performance and body composition of L.vannamei were studied.The results showed that,comparing with the control group,the weight gain and specific growth rate of the shrimp in three PHB treatment groups was significantly better than that of the control(P<0.05).The FCR in 3%PHB treatment group was significantly lower than the control(P<0.05).No significant difference was observed in the survival rate of shrimp of the four groups,and they were all above 96%(P>0.05).The results of body composition study showed that no significant difference was observed in the moisture and ash content between three PHB treatments and the control group(P>0.05).The content of crude protein in 3% and 5%PHB treatment group were both significantly higher than the control(P<0.05),and the content of crude lipid in 5%PHB treatment group increased significantly and higher than other three groups(P<0.05),but there were no significant difference in the control,1%PHB and 3%PHB treatment group(P > 0.05).These results indicate that diet supplementation of PHB dose could improve the growth performance and crude protein.Under this condition,the 3%PHB reflects the best results.2 Effects of PHB on intestine immune and digestive function of L.vannameiThe Intestine tissue structure,intestine SCFA content,immune and digestive enzyme activities and immune genes expression level in intestine of L.vannamei after PHB treatment was compared.After the intestine tissue of L.vannamei stained with HE dye,compared with the control group,the tissue of the three PHB group showed intestine epithelium connection closely and height increased,nuclei numbers increased significantly,and no sign of necrotic enterocytes or cell damage observed.The content of acetic acid in three PHB treatment groups were all significantly higher than the control,and with the increase in PHB concent increased(P<0.05).Compared with the control group,the content of propionic acid in 1% and 3%PHB treatment group was significantly higher,while butyric acid content of the 3%PHB treatment group was the highest(P<0.05).Compared with the control group,amylase,lipase and trypsin activities in the three PHB treatment groups were all significantly higher than that of the control(P<0.05).Amylase activity in 1%PHB group was the highest,but lipase activity of three PHB treatment groups were statistically the same with each other(P>0.05).Trypsin and pepsin activity in 3%PHB group was significantly higher than 1%PHB and 5%PHB group(P<0.05).LSZ activity was significantly induced in 5%PHB group(P<0.05),but there were no significant changes in 1%PHB and 3%PHB group(P > 0.05).T-AOC and iNOS activity of 3%PHB group were significantly higher than 1%PHB and 5%PHB group(P<0.05).NO content in the three PHB treatment groups were all significantly higher than that of the control(P<0.05).The relative expression level of HSP70 gene was induced significantly in the three PHB treatment groups,and the highest level was in 3%PHB group(P<0.05).The relative expression level of Toll gene increased gradually after PHB treatment(P<0.05).The relative expression level of Imd gene was induced significantly in the 1%PHB group(P<0.05),but no significant change was observed in the 3%PHB and 5%PHB group(P>0.05).These results indicate that diet supplementation of PHB could improve the intestine SCFA content as well as the hight of intestine epithelium,and enhance the digestion and non-specific immunity of L.vannamei.3 Effects of PHB on composition of intestine microbiota of L.vannameiThe results of the intestine microbiota composition showed that there are 467,497 original sequences were obtained after sequencing through Illumina HiSeq platform,and 463732 effective tags after selected.There were total 1442 OTUs and 458 common OTUs in three PHB groups and control group,and the OTU numbers decreased with the PHB concentration increased.Compared with the control group,the Chao1、ACE and Shannon index of 1%PHB was higher but the difference was not significant(P<0.05).The diversity of L.vannamei intestine microbiota was decreased while the PHB concentration increased and 5%PHB significantly lower than the control.Proteobacteria and Tenericutes was dominant in four groups,and the intestine dominant classes in four groups were Mollicutes,Alphaproteobacteria and Gammaproteobacteria.In addition,high doses of dietary PHB supplementation decreased the intestine microbiota diversity and increased the abundance of probiotics,such as Bacillus,Lactobacillus,Lactococcus,Bdellovibrio,and Clostridium. |
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