Effects And Mechanism Of Feeding Bacillus Coagulans On Intestinal Function Of Digestion And Absorption Of Broiler Chickens In Heat Stress

In this study,a strain of B.coagulans was isolated and purified,and the probiotics of B.coagulans were studied in vitro firstly.ELISA was used to detect content of total amylase and total protease in the bacterial solution of this strain of B.coagulans;after“adjustment pH”and high temperature treatment（90℃/10 min）,the inhibition effects of B.coagulans solutions with different treatment methods on Escherichia coli K88 and Salmonella pullorum were studied by Oxford cup method,and the antimicrobial substances of B.coagulans were initially judged.The content of total amylase and total protease in the culture solution of B.coagulans were determined by ELISA in vitro.The B.coagulans culture solution was treated with pH adjustment and high temperature（90℃,10min）.In animal experiments,320 28 day old AA broilers were divided into 5 groups with 8 replicates in each group（N=8）.The five treatment groups were as follows:（1）TC group:broilers were fed a basal diet at22±1℃;（2）HS group:broilers were fed a basal diet at heat stress with 34±1℃whole-day.（3）HS-BC_0.2group:whole-day heat stress at 34±1℃,the basal diet supplemented with 0.2×10⁷ CFU/g B.coagulans（complete compound feed）;（4）HS-BC_1.0 group:whole-day heat stress at 34±1℃,fed with basal diet supplemented1.0×10⁷ CFU/g B.coagulans;（5）HS-BC_5.0 group:whole-day heat stress at 34±1℃,5.0×10⁷ CFU/g B.coagulans.The experiment lasted from 28 to 42 days of age.The results showed as follows:1.B.coagulans culture for 24 h,the total amylase activity of the centrifuged supernatant solution was 3.55 U/m L and the total protease activity was 90.04 U/L.2.The inhibitory effects of B.coagulans culture solution（pH=4.7）on E.coli K88 and Salmonella pullorum were classified as“highly sensitive”and“sensitive”.The lactic acid solution at pH 4.7 showed“insensitivity”to E.coli K88 and Salmonella pullorum.When pH of B.coagulans culture solution was adjusted to 7.0,the inhibition effect of B.coagulans culture solution on Salmonella pullorum was“sensitive”,and there was no significant difference from the culture solution（P>0.05）.The bacteria culture solution was treated at high temperature（90℃/10 min）,and it had no inhibition effect on E.coli K88 and Salmonella pullorum,and the difference was significant（P<0.05）.In vitro bacteriostatic experiment showed:B.coagulans had good bacteriostatic performance,and when the pH of B.coagulans culture solution was adjusted to 7.0,there was no significant difference in the inhibition effect of B.coagulans culture solution on Salmonella pullorum（P<0.05）;when the culture solution was treated at90℃for 10 min,it was“insensitive”to Escherichia coli K88 and Salmonella pullorum,which was significantly different from the B.coagulans culture solution（P<0.05）.3.Compared with TC group,the ADG,ADFI,feed dry matter and crude protein apparent digestibility,total amylase and total protease activity of jejunum chyme,number of Lactobacillus in jejunum and cecum digesta and lactobacillus/E.coli value,jejunal villus height and VH/CD,jejunal tissue nutrient transporter mRNA expression of SGLT1,r-BAT,y+LAT1 in HS group were significantly decreased（P<0.05）,while F/G in HS group was significantly increased（P<0.05）.At the same time,the F/G,RT_42d,ΔT_28-42d and the number of E.coli in jejunum,ileum and cecum intestinal digesta were significantly increased（P<0.05）.4.Compared with HS group,the ADG,feed crude protein apparent digestibility,lactobacillus/E.coli values in jejunum and cecum chyme,jejunal tissue nutrient transporter mRNA expression of SGLT1,r-BAT,and y+LAT1 in both HS-BC_1.0 and HS-BC_5.0 groups were significantly increased（P<0.05）.Compared with the HS group,the height of jejunal villi and the VH/CD value of jejunal in HS-BC_1.0 group was significantly increased（P<0.05）,while the total protease and total amylase activity of jejunum chyme and the VH/CD value of jejunum in HS-BC_5.0 group was significantly increased（P<0.05）.In conclusion,this strain of B.coagulans has good enzyme producing and bacteriostatic characteristics.B.coagulans can improve the digestion and absorption ability of feed nutrients of broilers under heat stress by increasing the activity of intestinal digestive enzymes,regulating intestinal flora,maintaining intestinal morphology and promoting the expression of nutrient transporter protein in intestinal epithelial cells,thus improving the growth performance of broilers under heat stress.In addition,the dosage of 1.0～5.0×10⁷ CFU/g（full price feed）had significant effect.