| This experiment was designed to investigate the effect of Bacillus subtilis on the weight gain,intestinal morphology,immune organ index and immune response of Cherry Valley Ducks as well as the resistance to Escherichia coli and novel duck reovirus.Two hundred and forty one-day-old Cherry Valley Ducks with similar body weights and healthy weights were randomly divided into 2 groups.Each group had 3 replicates and 40 ducks were repeated.Group I was the control group and was fed basal diet.Group II was the experimental group and Bacillus subtilis was added to the basal diet at 1×10~6 CFU/g in a 35-days period.The effects of Bacillus subtilis on the weight gain and immune function of Cherry Valley Ducks were studied by measuring the bod y weight,intestinal morphology,immune organ index and the survival rate after E.coli and new duck reovirus in Cherry Valley Ducks.The q RT-PCR technique was used to detect the expression of immune-related genes in thymus and spleen,and the molecular mechanism of Bacillus subtilis enhancing immune function in Cherry Valley Ducks was further studied.The results are as follows:1.Weight gain:1-14 days after feeding,the difference of average total gain and average daily gain of the Cherry Valley Ducks fed with the Bacillus subtilis compared with the control group was not significant(P>0.05).14-28 days after feeding,the average total gain and average daily gain of ducks fed with the Bacillus subtilis was significantly higher than the control group,increased by 41.7%and 42.0%,respectively(P<0.05).During the 28 days,the average total gain and average daily gain of ducks fed with the Bacillus subtilis was significantly higher than the control group,increased by 21.9%and 21.7%,respectively(P<0.05).2.Intestinal morphology:The villus height of the duodenum and jejunum of the Cherry Valley Ducks fed with the Bacillus subtilis was significantly higher the control group,increased by 4.7%and 15.9%respectively(P<0.05),but there was no significant difference in the villus height of the ileum compared with the control group(P>0.05).The crypts depth of duodenal in the ducks fed with Bacillus subtilis was significantly lower than the control group(P<0.05),but there was no significant differe nce in crypt depth of jejunum and ileum compared with the control group(P>0.05).The ratio of villus height and crypt depth in the duodenum and jejunum fed with Bacillus subtilis was significantly higher than the control group,increased by 25.9%and 30.7%respectively(P<0.05),and the ratio of villus height to crypt depth in the ileum was not significantly different from the control group(P>0.05).It showed that Bacillus subtilis can improve the intestinal morphology and promote the digestion and absorption of nutrients by animals.3.Immune organ index:O n the 14th day after feeding,the thymus index,bursa index and spleen index of the Cherry Valley Ducks fed with Bacillus subtilis were significantly higher than the control group,increased by 52.4%,122.8%and 50%respectively(P<0.05).On the 28th day after feeding,only the bursa index of the Cherry Valley Ducks fed with Bacillus subtilis was significantly higher than the control group,whereas the spleen index and thymus index were not significantly different from the control group(P>0.05).It showed that Bacillus subtilis can promote the development of immune organs to some extent.4.The expression of Immune-related gene(1)Immune-related gene expression in thymus:On the 14th day,only RIG-I was significantly up-regulated in the group fed with Bacillus subtilis,but there was no significant defference in MDA5,TLR3 and TLR7 compared with the control group.On the 28th day,the expression of MDA5,RIG-I and TLR3 in Bacillus subtilis group was significantly up-regulated compared with the control group.The expression of MDA5 and TLR3 was up-regulated by 100-fold(P<0.01)and 97.64-fold(P<0.01)respectively.RIG-I expression has only been increased by 10 times.On the 14th day,the expression of IFN-αwas significantly up-regulated in Bacillus subtilis group compared with the control group,which was up-regulated by 3.73 times(P<0.01),while there was no significant difference in the expression of IFN-γand IFN-β.In addition,on the 28th day,the expression of IFN-αand IFN-γwere up-regulated by 4.56-fold and 14.69-fold(P<0.01)respectively,while the expression of IFN-βwas down-regulated by 0.24-fold(P<0.01).On the 14th day,compared with the control group,there were no significantly d ifference in IL-6,IL-8,IL-1βand IL-10of the group fed with Bacillus subtilis,but IL-6,IL-8,IL-1βand IL-10 were significantly up-regulated at 28 days,especially IL-6 expression was up-regulated 66.78-fold(P<0.01).On the 14th day,there was no significant difference in the expression of PKR,OAS and MX in the group fed with Bacillus subtilis compared with the control group.However,on the 28th day,the expression levels of PK R and MX were up-regulated by 12.33-fold and 104.99-fold(P<0.01)respectively.There was still no significant difference in the expression of OAS.(2)Immune-related gene expression in spleen:O n the 14th day,MDA5,RIG-I,TLR3and TLR7 were up-regulated in the Cherry Valley Ducks fed the Bacillus subtilis compared with the control group.Expression of MDA5,RIG-I and TLR3 was significantly increased at28 days(especially TLR3 expression was up-regulated by 920.29-fold,P<0.01),but there was no significant difference in the expression of TLR7.On the 14th day,compared with the control group,the Cherry Valley Ducks fed with Bacillus subtilis showed up-regulation of type I and type II interferon.Among them,the IFN-αwas up-regulated by 2.94-fold,the IFN-βwas up-regulated by 2.28 times and the IFN-γwas up-regulated by 2.54-fold(P<0.01).On the 28th day,IFN-γwas up-regulated by 6.63-fold(P<0.01)in the Bacillus subtilis group,but there was no significant difference in IFN-βexpression.On the 14th day,only IL-6 was up-regulated by 2.29-fold in the Bacillus subtilis group,while there was no significant difference in IL-1βand IL-8.At 28 days,the expression of IL-10 was significantly up-regulated,while there was no significant difference in IL-1β,IL-6 and IL-8.At 14 days.PKR and MX were up-regulated,while there were no significant difference in OAS expression.O n the 28th day,only antiviral protein MX was significantly up-regulated.It is indicated that Bacillus subtilis could activate pattern recognition receptors,induce the expression of cytokines and antiviral proteins,and enhance the innate immune response of Cherry Valley Duckss.5.Disease resistance:After infection with Escherichia coli and novel duck reovirus,the survival rate of ducks fed with Bacillus subtilis was significantly higher than the control group.After infection with E.coli,the survival rate of the duck fed with the Bacillus subtilis was 43.3%and the control group was 20%.After infection with the novel duck reovirus,the survival rate of the duck fed with the Bacillus subtilis was 100%,and the control group was83.3%.This is consistent with the above conclusions.Bacillus subtilis can improve the body weight of Cherry Valley Ducks,improve intestinal morphology,promote the development of immune organs,enhance innate immune responses,and improve the body’s resistance to disease.In summary,the addition of Bacillus subtilis to diets can improve the weight gain,intestinal morphology,the immune organ index and innate immune response and increase the resistance to E.coli and novel duck reovirus of Cherry Valley Ducks. |
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