| At present,the"extended layer breeding"plan has been proposed in many countries,which extends the elimination time of laying hens from the traditional 72 weeks of age to80-100 weeks of age,making the economic benefits of laying hens in the late laying period after the peak of laying become more and more important in the breeding industry.Some intensive farms in countries such as the United States,Brazil,Germany and the Netherlands have already achieved the goal“500 eggs in 100 weeks of age”laying hens.However,in the process of intensive culture,laying hens are prone to metabolic disorders in the late laying period,which may lead to liver injury,after continuous high-load metabolism in the peak laying period.In particular,the liver as the main synthetic organ,is responsible for the de novo synthesis of 84%of yolk precursors and more than 90%of fats,as well as the synthesis of 85%-90%of circulating proteins,so it is more vulnerable to injury.Seriously affect the body health level and production performances.Therefore,the prevention of liver injury in the late laying period is directly related to the health level and production performances level of laying hens,and is a very important link to ensure the economic benefits of laying hens in the late laying period.After the Chinese government forbidden antibiotics in feed,which affected the body health,performance and feed conversion efficiency of livestock and poultry in large-scale farms.Taurine as a nutritional fortification agent has physiological functions such as regulating energy metabolism,lipid metabolism,antioxidant and anti-inflammatory,etc.It has been widely used in food and medicine fields,and its role in large-scale livestock and poultry breeding after feed resistance ban has attracted more and more scholars’attention.The application of taurine in improving the performance of laying hens and piglets has been reported,but there is a lack of recommended dosages and standard specifications.The prevention effects and mechanisms of liver injury in laying hens during late laying period are rarely reported.Our previous studies have shown that taurine has a good effect on the prevention of non-alcoholic fatty liver disease in laying hens,but the recommended dosage is still unclear and the specific mechanism of action needs to be further explored.102 Lohmann pink-shell laying hens aged 44 weeks in late laying period were randomly divided into 6 groups with17 replicates per group and fed in a single cage.The control group was fed a basal diet at 45to 46 weeks of age in the preliminary test and 47 to 62 weeks of age in the formal test.The3 treatment groups were fed the basal diet supplemented with 0.01%,0.02%,0.05%,0.10%and 0.20%taurine.The liver histopathology and serum liver function indexes were analyzed to study the intervention effect of taurine on liver injury of laying hens in late laying period.Determination of liver transcriptome and metabolome revealed the mechanism of taurine on liver injury of laying hens in late laying period.The main results are as follows:（1）Liver structure injury:The liver histopathological analysis showed that the liver surface of laying hens at 62 weeks of age in late laying period was significantly yellow compared with that of laying hens at 46 weeks of age in peak laying period,and there were obvious fat vacuoles,inflammatory cell infiltration and orange fat droplet deposition,which was judged to be liver structure injury.The liver surface of 62 weeks of age laying hens fed 0.05%,0.10%and 0.20%taurine showed normal bright red,without significant fat vacuoles,inflammatory cell infiltration and orange fat droplets deposition.Taurine remission liver structure injury.（2）Liver function injury:The analysis of serum liver function indexes showed that the levels of alanine aminotransferase and aspartate aminotransferase,total bilirubin and direct bilirubin,triglyceride and total cholesterol in serum of laying hens aged 62 weeks in late laying period were significantly increased compared with those of laying hens aged 46weeks in peak laying period（P<0.05）,and the levels of total protein and albumin were significantly decreased（P<0.05）.It was judged to be liver function injury.The levels of alanine transaminase and aspartate transaminase,total bilirubin and direct bilirubin,triglyceride and total cholesterol in serum of 62 weeks of age laying hens fed 0.05%,0.10%and 0.20%taurine were significantly decreased（P<0.05）,and the levels of total protein and albumin in serum were significantly increased（P<0.05）.Taurine remission liver function injury.（3）Remission liver injury mechanisms:In the late laying hens diet adding 0.10%taurine compared with control group,the transcriptomes analysis of selected 535differentially expressed genes,according to the differences in fold change|log2FC|biggest selected 30 core differentially expressed genes,The up-regulated genes were ST6GALNAC3,SLC30A2,MHCIA2,RAB3C,KIAA1324,new Gene-2148,NEXN,new Gene-5753,KCTD16,GALNT9,KCNJ16,LSAMP,new Gene-5794 and S GIP1;Down-regulated genes were IL411,EXFABP,AVD,CSF3,SLC6A14,new Gene-714,PI3,HPS5,LOC101750892,PTGER3,FGF19,PLA2G3,OTOP2,LOC417056,PCK1 and new Gene-3377.It mainly disturbs MAPK signaling pathway.Metabolomic analysis of metabolites,27 kinds of differences according to the different variable projection importance and fold change|log2FC|biggest 10 core of core differences metabolites,which improve theβ-indole-3-acetic acid,Putrescine,2’-O-methylguanosine,Dihydrothymine and Biopterin level,it reduces the levels of Quinoline 2-carboxylic acid,5α-Pregnane-3,20-dione,3β-Cholic Acid,3-Chloro-L-Tyrosine and Octadecanedioate（C18）,mainly perturbs the steroid hormone biosynthesis.In the transcriptomes and metabolomes interaction mechanism,taurine mainly regulates core differentially expressed genes NEXN,gallus-new Gene-2148,LSAMP,gallus-new Gene-5794,LOC417056,ST6GALNAC3,KCNJ16 and PCK1 were associated with the core differential metabolites Quinoline 2-carboxylic acid,β-ndole-3-acetic acid,5α-Pregnane-3,20-dione,Putrescine,Dihydrothymine,3-Chloro-L-Tyrosine and Biopterin in order to remission liver injury of laying hen in late laying period.In summary,the main conclusions of this study are:Taurine can effectively remission liver structure injury and liver function injury of laying hens in late laying period.The MAPK signaling pathway was mainly disrupted by up-regulating the expression of key genes such as NEXN,gallus-new Gene-2148 and gallus-new Gene-5794 in liver and down-regulating the expression of key genes such as IL411,EXFABP and AVD in liver.In addition,increasingβ-ndole-3-acetic acid and decreasing Quinoline 2-carboxylic acid level disturbed the steroid hormone biosynthesis and played a role in remission liver injury.The effects and mechanisms of taurine in remission liver injury of laying hens in late laying period will provide a new nutritional regulation strategy for improving the health and performance of laying hens in late laying period. |
