| Four experiments were conducted to explore the effects of Lactobacillus acidophilus on intestinal development and health,and the omics mechanism of differential gut development of broilers.Exp.l was conducted to investigate the effects of Lactobacillus acidophilus on intestinal development and intestinal microflora.This trial was designed as a single-factor experiment,300 Cobb broiler chickens aged 1 day were randomly divided into 3 treatments(control group,group supplemented with aureomycin and group supplemented with Lactobacillus acidophilus)with 10 replicates per treatment and 10 chickens each replicate.The results showed addition of aureomycin increased the body weight of broilers on day 28,and the ADG(average daily gain)of broilers during the 28-day experimental period,increased the total weight of small intestines,decreased the weight percentage of duodenum to the small intestine,and increased the percentage of the weight of jejunum to the total weight of the small intestine,significantly decreased the concentration of endotoxin in the plasma.The body weight on day 28,and the ADFI(average daily feed intake)and ADG during the 28-day experimental period were significantly increased by adding Lactobacillus acidophilus to the diet.The addition of Lactobacillus acidophilus also significantly increased the weight of the small intestine,the length of duodenum,significantly decreased the weight percent of duodenum/total small intestine,and significantly increased the villus height,villus height/crypt depth ratio,mucosal thickness and intestinal wall thickness in the ileum,and significantly decreased the concentration of endotoxin in the plasma.In conclusion,Lactobacillus acidophilus promoted intestinal development,and improved growth performance of broilers.Exp.2 was conducted to examine the effects of Lactobacillus acidophilus(L.acidophilus)on the growth performance and intestinal health of broiler chickens challenged with Clostridium perfringens(C.perfringens)over a 21-day period using a 2 × 2 factorial arrangement of treatments.During infection(d 14-21),C.perfringens challenge decreased the average daily gain,and increased feed conversion ratio and the mortality rate.However,dietary supplementation with L.acidophilus increased the body weight of C.perfringens-infected broilers on d 21,and tended to decrease the mortality.Clostridium perfringens infection decreased the villus height,the ratio of villus height to crypt depth and OCLN(occludin)mRNA expression,and increased the pro-inflammatory cytokine expression in the spleen and jejunum,and the serum content of endotoxin,regardless of L.acidophilus supplementation.In contrast,dietary L.acidophilus reduced the intestinal lesion score of infected broilers,the mRNA expression of pro-inflammatory cytokines,and serum endotoxin content.The infection decreased the observed species,chaol and ACE of ileal microbiota and increased the chaol of cecal microbiota of broilers,and L.acidophilus supplementation decreased the Shannon index of ileal microbiota.The Shannon index and simpson of ileal microbiota were lower than that of cecal microbiota.In the ileal microbiota,the relative abundance of Lachnospiraceae and Ruminococcaceae was higher in the control group in comparison with other groups,however,the relative abundance of Gammaproteobacteria was significantly higher in the challenge group(CLG)compared with other groups.Clostridium perfringens infection tended to increase the lactate concentration,and decreased the concentrations of formate,acetate and propionate in the ileum,and decreased the isobutyrate concentration and tended to decrease the i-velerate concentration in the cecum.And L.acidophilus addition in the diets increased the concentration of lactate and butyrate,and decreased the concentrations of formate and propionate in the ileum,and increased the concentration of lactate and velerate in the cecum.In conclusion,dietary addition of L.acidophilus could improve the intestinal health and reduce the mortality of broilers suffering from necrotic enteritis.Exp.3 was conducted to compared the differences in the ileal microbiota,metagenomes of the microbiota and ileal transcriptomes of two types of small intestines—intestines with thick walls(TK group)or thin walls(TN group)by 16S rRNA gene sequencing within the V3-V4 region,metagenomic analysis and RNA-sequencing in order to determine the molecular basis for the developmental differences of the small intestine.The differences in microbial communities among the ilea with different wall thicknesses were quite significant;i.e.,the relative abundance of the Firmicutes plylum was significantly higher in the ileal microbiota of the TK group than in that of the TN group,while the relative abundance of the Bacteroidetes phylum was significantly lower in the TK group than in the TN group.The relative abundance of the Lactobacillus genus was significantly higher,while the relative abundance of the Alistipes genus and Bacteroides genus of the Bacteroidetes phylum were lower in the ilea of the TK group than in those of the TN group.The ileal wall thickness was positively correlated with the relative abundance of the ileal Lactobacillus genus,whereas negatively correlated with relative abundance of the Bacteroides and Alistipes genera in the ilea of broiler chickens.Whole microbial genome sequencing analysis indicated that most of the microbial functions associated with cysteine and methionine metabolism,lysine biosynthesis,tryptophan metabolism,carbon metabolism,starch and sucrose metabolism,galactose metabolism,pyruvate metabolism,glycolysis/gluconeogenesis,oxidative phosphorylation,the pentose phosphate pathway,propanoate metabolism,and the citrate cycle(TCA cycle)were significantly enhanced in the ilea of the TK group compared with the ilea of the TN group.Transcriptomic analysis suggested that cell proliferation,energy metabolism,and polypeptide and lipid synthesis are more active in the ilea of the TK group than in the ilea of the TN group.The results of serum metabolome showed that the pathway of ketone bodies was activated in the broilers with thin ileal wall,and its basal metabolism required more fat,glycogen,and protein;broilers with thick ileal wall had more converted glutamate through pathways such as alanine,aspartate and glutamate matabolism,and could promote intestinal development.In conclusion,the structure and function of microflora of broilers with different ileal wall thickness were significantly different,and the intestinal transcriptome and serum metabolome also changed significantly.The intestine with thicker was more mature.Intestinal Lactobacillus and other probiotics were positively related to the normal development and function of the intestinal tract.Exp.4 was conducted to compare the difference of liver transcriptome of broilers with thick ileal wall or thin wall under normal rearing condition.The results showed that the thickness of ileal wall was positively correlated with body weight,but negatively correlated with liver index.Compared with the broiler chickens with thin ileal wall,there were 694 upregulated genes and 664 downregulated genes in the liver of broiler chickens with thick wall.The livers of broiler chickens with thick ileal wall were more mature than the broiler chickens with thin ileal wall.And the biosynthesis of carbohydrate,lipid and amino acid and the transport of amino acid and protein were more active in the livers of broiler chickens with thick ileal wall compared with the broiler chickens with thin ileal wall.In conclusion,the processes of biosynthesis and transport were more active in the livers of broiler chickens with thick ileal wall compared with the broiler chickens with thin ileal wall.In conclusion,Lactobacillus acidophilus could promote the intestinal development,improve intestinal health and enhance disease resistance ability of broilers;there were significant difference in the composition and function of intestinal microbiot of broilers with thick or thin ileal wall,the Lactobacillus genus in the small intestine was positively correlated with the normal development and function of the gut,and the intestine with thick ileal wall was more mature,and had enhanced absorptive capacity and metabolic capacity;in addition,the processes of biosynthesis and transport were more active in the livers of broiler chickens with thick ileal wall compared with the broiler chickens with thin ileal wall. |
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