Effects Of Anti-inflammatory Egg Yolk Antibody On The Growth Performance And Intestinal Health Of The Large-scale Loach Paramisgurnus Dabryanus

Objective:Intestinal inflammation is one of the main diseases of farmed fish in aquaculture.The use of antibiotics in aquaculture may bring great risk to food safety.The application of modern biotechnology products for the prevention of fish diseases has become an important research field in fish pathology.In this study,we performed experiments to examine the effects of supplementing feed with anti-inflammatory egg yolk antibody on growth performance and intestinal health of the large-scale loach Paramisgurnus dabryanus.Methods:The large-scale loach with initial weight of 9.8±0.5 g was used as the experimental objects.The fish meal and fish oil were included in the basal diet（35.42%crude protein）as main protein and fat sources,respectively.The egg powder containing anti-inflammatory antibody was added into the basal diet at 1.0,2.0,4.0,and 6.0 g/kg,respectively.As control,the egg powder without anti-inflammatory antibody was added at 6.0 g/kg.Three replicates were set for each treatment.The fish were reared in plastic tanks（30×30×100 cm³）with aerated tap water（25±2?C）.One-third of the water was replaced every two days.The fish were fed twice daily at 8:30 and 16:30 in the amount of 1.0².5%of their body weight.The feeding amount was timely adjusted based on feed intake situations.Eight weeks after feeding trial,the growth performance parameters were determined,the biochemical and immunological indexes were measured,the morphological characteristics of the fish intestines was examined,and the intestinal microbiota were analyzed.Results:1.The effects of anti-inflammatory antibody on the growth performance and digestive enzymes of the large-scale loachThe weight gain rate and specific growth rate in treatment groups were17.1³4.5%,0.28⁰.53%d^-1,respectively.Compared with the control group,the weight gain rate and specific growth rate gradually increased with the dose of anti-inflammatory antibody supplemented into the basal diet.Significant differences were observed when anti-inflammatory antibody-contained egg powder was added at2.0 g/kg and even more（p<0.05）.In treatment group with addition at 4.0 g/kg,the weight gain rate and specific growth rate increased by 101.8%and 89.3%d^-1 more than that of the control group.The coefficients of feed were 1.23¹.05 in all groups,all being significantly lower than those of control（p<0.05）.The addition levels at 2.0⁴.0 g/kg resulted in the lowest feed coefficient,and decreased by 17.14%than that of the control group.The highest intestinal amylase activity was detected when the egg powder containing anti-inflammatory antibody was added at a level of 1.0 g/kg,which increased by 31.25%more than that of the control group（p<0.05）.The activities of lipase,trypsin,and cellulose in the large-scale loach were increased by 79.12%,236.62%,and 28.13%more than those of the control group（p<0.05）when the addition level was as high as2.0 g/kg.The protease activities of liver from treatment groups with addition level higher than 2.0 g/kg significantly or extremely significantly increased by 14.4⁵6.4%（p<0.05）.2.The effects of anti-inflammatory antibody on the anti-oxidative capacity and anti-infection ability of the large-scale loachThe anti-inflammatory egg yolk antibody was found to enhance the liver anti-oxidative capacity and anti-infection ability of the large-scale loach.The liver index of the large-scale loach increased when the anti-inflammatory egg yolk antibody was supplemented with egg powder into the basal diet at an addition level higher than 2.0g/kg.When addition level achieved 4.0 g/kg,the liver index increased by 68.3%,significantly higher than that of control（p<0.05）.In the treatment groups with addition amount between 2.0 g/kg⁴.0 g/kg,the contents of glutamic and intestinal SOD significantly higher than those in the control liver（p<0.05）,while both of the MDA contents and the myeloperoxidase（MPO）activities were significantly lower（p<0.05）.The lowest MDA content in the loach intestine was measured when the addition level was 2.0 g/kg,and decreased by 83.3%than that of the control group.There was a significant difference in the cumulative mortality rate of the fish between control and treatment groups（p<0.05）at 7 d following challenge with Aeromonas hydrophila.The cumulative mortality rate reached 100%in control group,while the values in treatment groups were 53.3⁶6.7%.The lowest cumulative mortality rate（53.3%）was obtained in the treatment group with addition level at 2.0 g/kg.3.The effects of anti-inflammatory antibody on the morphological characteristics of the large-scale loach intestinesApplication of anti-inflammatory antibody caused the changes in morphological characteristics of the large-scale loach intestines,including the increments in intestine length,kerckring height and width of midgut,and thickness of the muscular layer.When the addition level achieved 2.0⁴.0 g/kg,all these parameters were superior to the control group（p<0.05）.The morphology and ultrastructure of intestinal endothelial cell surface were observed.The results showed that the long,uniform,and closely arranged microvilli,and smooth inner surface were found in the endothelial cell surface from treatment groups with addition level at 2.0⁴.0 g/kg,while in the control group,the microvilli with distinct length were arranged sparsely.Therefore,the intestinal structures of fish from treatment groups were superior to the control group,which will strengthen the intestinal barrier function.4.The effects of anti-inflammatory antibody on the intestinal microbiota of the large-scale loachThe sequence analysis of 16S rRNA of intestinal bacteria showed that the bacterial richness indexes,Ace and Chao,increased after the anti-inflammatory antibody was applied.The indexes Ace and Chao increased by 20.6³9.3%,25.9⁴6.1%,respectively,than those of the control group.Shannon diversity index in each treatment group was significantly higher than that in control group except that in the group with addition at 1.0 g/kg,the index was lower than that of control.The amount of the probiotic Lactobacillus in intestines from treatment groups was 8²13 times higher than the control group.Conclusions:The anti-inflammatory egg yolk antibody effectively improved the growth performance of the large-scale loach,enhanced the digestive enzyme activities and the liver anti-oxidative capacity and anti-infection ability of the large-scale loach.The antibody was also proved to increase the richness index of the intestinal microbiota,particularly that of probiotic Lactobacillus.In addition,after use of anti-inflammatory egg yolk antibody,the intestines elongated,the kerckring height and width,and the muscular layer thickness were elevated,and the microvilli were elongated and arranged densely.Therefore,the intestinal barrier function was improved by application of the antibody.All these results taken into consideration,the appropriate supplemental amounts of the anti-inflammatory egg yolk antibody were 2.0⁴.0 g/kg.