| Objective: Immune function of chicken is the basis of resisting pathogen invasion,maintaining digestive tract health and improving productivity.In practice,feed acidifiers are often used to improve the performance of laying hens or broilers.In present study,metaanalysis was hired to figure out the potential and application value of short-chain fatty acid acidifiers for enhancing avian immune function with various immune indicators.Subsequently,specific animal experiments,both in laying hens and in broilers,were carried out to reveal the regulatory function on chicken immune system.Methods:(1)Literature databases of CNKI,Wan Fang,Web of Science and Pub Med were explored to collect the related studies of short-chain fatty acids and their derivatives on animal immune function.Review Manager 5.3 and Addis 1.16.8 software were used to evaluate the effects of short-chain fatty acids on various immune indexes with direct metaanalysis and network meta-analysis.(2)HY-Line Brown laying hens aged 270 days were randomly divided into two groups with 144 animals in each group according to body weight.Animals in the control group were fed with basal diet,and animals in experimental group were fed with basal diet supplemented with 1 g/kg glycerol butyrate compound product daily for 60 days.At the end of the trial,twelve laying hens were randomly selected from each group,body weight and immune organ weight were recorded to calculate the immune organ index.After sampling blood,serum and plasma were separated to detect the antibody titers of Newcastle disease and biochemical indexes in blood.Immune organs were collected to determine the expression of immune-related genes.(3)One-day-old Partridge Shank broilers were randomly divided into two groups,with 60 broilers in each group.The control group was fed with basal diet,and the experimental group was fed with basal diet containing 1 g/kg tributyrin.Samples were taken after 21 and 45 days of feeding.Body weight and immune organs weight were recorded to calculate the immune organ index.Blood and immune organs were sampled and determined in the same way described in above layers experiment.Here,antibody titers of avian influenza H5 and H7N9 were additionally detected.Results:(1)Direct meta-analysis results showed that short-chain fatty acids could improve Ig M content,lymphocyte count and antibody titer in peripheral circulation.Short-chain fatty acid salt could increase the contents of Ig G,Ig M,Ig A,globulin,lymphocyte number and complement activity,and reduce the content of pro-inflammatory cytokines.Significant effects on enhancing Ig G content and lysozyme activity were observed about short-chain fatty acid glycerides in current analysis model.Furthermore,short-chain fatty acids were better to improve lysozyme activity than short-chain fatty acids salts when investigated with network meta-analysis.In terms of other immune indexes,there were no significant differences among short-chain fatty acids,short-chain fatty acids salts and short-chain fatty acids glycerides,but all better than basal diet.(2)Compared with the control group,the contents of glutamic-pyruvic transaminase,glutamic-oxalacetic transaminase and alkaline phosphatase in plasma of laying hens with treatment were significantly increased(P < 0.01),meanwhile the contents of triglyceride and HDL-c were significantly decreased(P < 0.05).Serum antibody titer of Newcastle disease was significantly higher in treatment group(P <0.01).The m RNA abundance of My D88 in liver was significantly increased(P < 0.05),but significantly decreased(P < 0.05)in spleen associated with TNF-α expression significantly decreased(P < 0.05).Interestingly,AVBD9,one of the most important avian defensins,was found significantly increased in thymus of treatment animals(P < 0.05).(3)Studies on oneday-old broilers showed that the plasma albumin content of 21-day-old broilers in treatment group was significantly lower than control group(P < 0.05).The antibody titer of Newcastle disease of 21-day-old broilers and avian influenza H5 of 45-day-old broilers were significantly higher with tributyrate treatment(P < 0.05).The gene expression results showed that tributyrate significantly up-regulated the gene expression of AVBD9 in the spleen of broilers at 21 days of age(P < 0.05).The m RNA abundance of TLR-2,TLR-4,NF-κB and pro-inflammatory cytokines IL-8(P < 0.05),IL-1β(P < 0.05)and IFN-β(P < 0.01)of broilers at 21 days of age were significantly decreased.Spleen TLR-2 was down-regulated in of 45-day-old broilers,associated with antimicrobial peptide Cath-B1 up-regulated(P < 0.05).In thymus,more inflammatory or immune-related genes,including TLR-2,TRAF-6,TRIF,NF-κB,TNF-α and TGF-β1(P < 0.01),expression of TLR-4 is also down-regulated(P < 0.05),My D88 were significantly down-regulated(P < 0.01)in tributyrate broilers,associated with the up-regulation of IL-8(P < 0.05)and AVBD9(P < 0.01).The m RNA expressions of TLR-2(P < 0.01),TLR-4(P < 0.05),IFN-β(P < 0.01),My D88(P < 0.05),and AVBD9(P < 0.01)in bursal of fabricius at 45 days of age were significantly down-regulated,and the gene expressions of TRIF(P < 0.05),NF-κB(P < 0.01),TGF-β1(P < 0.01)and IL1β(P < 0.05)were up-regulated by tributyrin treatment.Conclusion:(1)Short-chain fatty acids,short-chain fatty acid salts and short-chain fatty acid glycerides could improve immune function in whole to different degrees with no significant difference between each other,but they were considered to be better on immune regulation than basal diet.(2)Dietary supplementation of butyric acid glyceride with 1 g/kg could increase the level of body-specific antibodies,up-regulate the gene expression of antimicrobial peptides and down-regulate the gene expression of pro-inflammatory cytokines in immune organs,which revealed the extremely application value of butyric acid glyceride,especially tributyrin,in improving the avian immune function. |
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