| This experiment was conducted to investigate the effects of Bacillus subtilis on growth performance,immune function and intestinal health of broiler chickens challenged with coccidia and Clostridium perfringens.A total of 450 1-day-old AA male broilers were randomly divided into five groups: A control group(basal diet),B challenge group(basal diet + challenge),C antibiotic group(basal diet + 12 mg/kg Enramycin + challenge),D low-dose probiotic group(basal diet + 300 mg/kg Bacillus subtilis + challenge)and E high-dose probiotic group(basal diet + 500 mg/kg Bacillus subtilis + challenge).Each group consisted of 6 replicates with 15 birds per pen.Broilers in groups B,C,D and E were challenged with coccidia at 14 days of age and Clostridium perfringens at 19 to 21 days of age,respectively.Broilers were kept in cage and both diets and water supplied ad libitum.The experiment lasted for 28 d.The results are as follows:1)Compared with group A,the feed to gain of broilers in group B was significantly increased during days 22～42 and 1～42(P<0.05).However,compared to group B,the feed to gain of broilers in groups C and D was significantly reduced during days 22～42 and 1～42(P<0.05).Besides,the average daily gain of broilers in group D was significantly than that in group B(P<0.05).Compared with group C,the average daily food intake of broilers in group D was remarkably increased(P<0.05),while the average daily gain and final body weight of broilers in group E were decreased(P<0.05)and the feed to gain was increased(P<0.05).Compared with group E,the average daily gain from days 1～42,the average daily food intake from days 1～21and the final body weight at days 21 and 42 of broilers in group D were higher(P<0.05)and the feed to gain from days 22～42 and 1～42 was lower(P<0.05).2)Compared with group A,the intestinal lesion scores of duodenum,jejunum and ileum of broilers at 28 and 35 days in group B were significantly increased(P<0.05).Compared with group B,intestinal lesion scores of broilers in groups C,D and E were significantly lower(P<0.05),and there was no significant difference compared with group A at 35 days(P< 0.05).3)Compared with group A,the contents of IgA,IgG and IgM in blood of broilers at 28 and 35 days in group B were not significantly different(P<0.05).At day 35,compared with group C,serum IgG and IgM contents of broilers in group D and IgM content of broilers in group E were increased(P<0.05).At day 35,compared with group E,IgG content in blood of broilers in group D was increased(P<0.05),but the serum IgM level was decreased(P<0.05).4)Compared with group A,thymus index of broilers at day 35 in group B was increased(P<0.05).Compared with other groups,the spleen index of broilers at day 28 in group D was significantly increased(P<0.05).5)At day 35,compared with group A,diamine oxidase activity in blood of broilers in group B was higher(P<0.05).Compared with group B,diamine oxidase activity in blood of broilers in group C was significantly decreased(P<0.05).6)At day 28,compared with group A,the jejunal ratio of villus heights to crypt depths,ileal villus height and villus heights to crypt depths ratio of boilers in group B were decreased(P<0.05),but jejunal and ileal crypt depth values were increased(P<0.05).Compared with group B,crypt depths of ileum of broilers in groups C,D,and E was decreased(P<0.05),villus heights and the villus heights to crypt depths ratio of ileum in group D were higher(P<0.05).Compared with group C,villus heights of duodenum of broilers in group D was increased(P<0.05).At day 35,compared with group A,jejunal villus heights and the villus heights to crypt depths ratio and the ileal villus heights to crypt depths ratio of broilers in group B were reduced(P<0.05),but crypt depths of jejunum and ileum was higher(P<0.05).Compared with group B,the ileal villus heights to crypt depths ratio of broilers in group E was higher(P<0.05)and ileal crypt depths was decreased(P<0.05).In addition,compared with group B,villus heights of duodenum and the villus heights to crypt depths ratio of jejunum and ileum of broilers in group D were increased(P<0.05),and crypt depths of jejunum and ileum was decreased(P<0.05).7)Compared with group A,the group B increased jejunal TNF-α,IFN-γ,NF-κB and IL-6 m RNA expression on days 28 and 35(P<0.05).Compared with group B,the m RNA abundance of TNF-α,NF-κB and IL-6 on days 28 and 35 and the m RNA abundance of IFN-γ on day 35 of jejunum in group C,D and E were downregulated(P<0.05).Compared with C group,the jejunal NF-κB m RNA expression on day 28 in groups D and E was decreased(P<0.05),and jejunal IL-6 m RNA expression on day 35 was increased(P<0.05).Compared with group E,the group D upregulated IL-6 expression in jejunum on day 35(P<0.05).8)On days 28 and 35,there were no significant differences in the cecal microbiota alpha diversity among the five groups(P>0.05).At the phylum level(top 7 in relative abundance ranking),compared with group A,the group B decreased the relative abundance of cecal Actinobacteria on day 28.At the genus level(top 7 in relative abundance),there were no significant differences in the relative abundance of bacteria between group A and B(P >0.05),and compared with group B,the relative abundance of Ruminococcus on days 28 and35 in group C and D was significantly increased.(P < 0.05).+In conclusion,Bacillus subtilis can replace enramycin to alleviate the negative effects of coccidiosis and Clostridium perfringens challenge on broilers,and improve the production performance,immune function and intestinal health to a certain extent,and the dosage of 300 mg/kg is better. |
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