Effects Of Dietary Folic Acid And Vitamin B₁₂ On Performance And Intestinal Barrier Function Of Laying Hens

The aim of this study was to investigate the effects of dietary different levels of folic acid and vitamin B₁₂(VB₁₂)on performence,egg quality,serum parameters,intestinal tissue morphology,intestinal barrier related gene expression and the caecal microflora structure of Jinghong laying hens at peak production.A total of 972 Jinghong laying hens at 28 weeks of age were randomly divided into 9 groups with 6 replicats per group and 18 hens per replicate.A two factors and three levels experimental design was use,the experimental diets were supplemented with folic acid and VB₁₂ at different doses in the basal diet,the folic acid was set at three supplemental levels of 0,2 and 5 mg/kg,and VB₁₂ was set at three supplemental levels of 0,25 and 75 μg/kg,respectively.The adjustment period lasted for 2 weeks,and the experimental period lasted for 8 weeks.The results showed as follows: 1)dietary folic acid and VB₁₂ and their interaction had no significant effects on performance of Jinghong laying hens（P>0.05）;Dietary 2 mg/kg folic acid significantly increased the egg shape index,egg shell thickness,yolk color and haugh unit（P<0.05）,25μg/kg VB₁₂ significantly increased the egg shell thickness,yolk color and haugh unit（P<0.05）,and their interaction significantly increased the haugh unit（P<0.05）.2)Dietary folic acid and VB₁₂ significantly increased the levels of serum immunoglobulin G（Ig G）and serum immunoglobulin M（Ig M）antibody synthesis in serum（P<0.05）,significantly decreased the serum endotoxin（ET）content（P<0.05）.Adding 2mg/kg folic acid and 25 μg/kg VB₁₂ significantly increased the levels of serum immunoglobulin A（Ig A）,serum immunoglobulin G（Ig G）and serum immunoglobulin M（Ig M）antibody synthesis in serum（P<0.05）,and significantly decreased the serum ET content and diamine oxidase（DAO）activity（P<0.05）.3)Dietary2 mg/kg folic acid significantly increased the villi height and villi height/crypt depth of jejunum and ileum（P<0.05）,25 μg/kg VB₁₂ significantly increased the villi height and villi height/crypt depth of duodenum（P<0.05）.The interaction of folic acid and VB₁₂ had a significant effect on villi height and villi height/crypt depth of duodenum and jejunum（P<0.05）,and adding 2 mg/kg folic acid and 25 μg/kg VB₁₂ significantly improved villi height and villi height/crypt depth of duodenum and jejunum than untreated group（P<0.05）.4)Dietary folic acid and VB₁₂ and their interaction had significant effects on Occludin and MUC2 mRNA expression levels of duodenum and jejunum（P<0.05）,and adding 2 mg/kg folic acid and 25 μg/kg VB₁₂ were significantly higher than untreated group（P<0.05）;Dietary 2 mg/kg folic acid significantly decreased the TLR4,NF-κB,TNF-a and IL-1β m RNA expression levels（P<0.05）,significantly increased IL-13 and SIg A m RNA expression levels（P<0.05）,25 μg/kg VB₁₂ significantly decreased the TLR4 and TNF-a m RNA expression levels（P<0.05）,significantly increased the SIg A and IL-10 m RNA expression levels of duodenum,jejunum and ileum（P<0.05）.The interaction of folic acid and VB₁₂ had a significant effect on TLR4,NF-κB,TNF-a,IL-1β IL-10 and SIg A m RNA expression levels of duodenum and jejunum（P<0.05）,and adding 2 mg/kg folic acid and 25 μg/kg VB₁₂ were significantly decreased the TLR4,NF-κB,TNF-a and IL-1β m RNA expression levels（P<0.05）,increased SIg A and IL-10 m RNA expression levels than untreated group（P<0.05）.5)The interaction of folic acid and VB₁₂ had a significant effect on species abundance and diversity of intestinal microflora（P<0.05）.In species level,and the Bacteroidetes,Firmicutes and Proteobacteria changed obviously.In genus level,the abundance of Bacteroides,Rikenellaceae_RC9_gut_group,Ruminococcaceae_UCG-014 and Barnesiella had significantly enrichment（P<0.05）,Desulfovibrio and Lachnoclostridium significantly decreased（P<0.05）.In conclusion,appropriate dietary with folic acid and VB₁₂ can improve the egg haugh unit,serum immune parameters,intestinal tissue morphology,and comprehensively improve the intestinal physical,chemical,immune and microbial barrier functions and promotes the healthy development of the intestinal tract.It is better to add 2mg/kg folic acid and 25 μg/kg VB₁₂ to the diet(containing 1.35 mg/kg folic acid and 25 μg/kg VB₁₂).