Effects Of Bacillus Subtilis On Immunity,antioxidation And Intestinal Morphology And Microbial Diversity Of Broilers

In the past half century,due to the extensive use of antibiotics,the problems such as the increase of bacterial resistance,animal residues and environmental pollution have become increasingly prominent.At present,the search about antibiotic substitutes has become a research hotspot.Many studies have shown that probiotics can improve the production performance of livestock and poultry.Bacillus subtilis is a kind of probiotics,and its substitution effect has become the main research object,but it mainly focuses on the growth performance of animals,and the growth regulation mechanism is not clear.The purpose of this experiment is to study the effect of Bacillus subtilis on the growth performance,slaughter performance,meat quality,immune status,antioxidation,intestinal morphology and cecal microbiota diversity of broilers,and evaluate the effect of Bacillus subtilis replacing bacitracin zinc and its possible growth promoting mechanism from multiple perspectives.Two hundred and seventy male broilers of 1-day-old were randomly divided into 3 groups with 6 replicates in each group,15 chickens in each replicate.The negative control group(NC)was fed with basal diet and the positive control group(PC)was fed with 250 mg/kg bacitracin zinc added to the basal diet,while the test group(BS)was fed with 750 mg/kg Bacillus subtilis added to the basal diet.The trial period was 42 days,which was divided into two phases: 1-21 days and 22-42 days.At the beginning and end of each stage of the experiment,the weight of broilers and the weight of surplus feed were weighed repeatedly by replicates to determine the growth performance of broilers.At the end of the experiment,one chicken was selected per replicate.After collecting blood from pterygoid vein,the bird was euthanized by severing the jugular vein and dissected,then slaughter performance was determined.Serum,liver,intestinal segment and chyme samples were collected and measured.The results are showed as follow:(1)Compared with NC group,Bacillus subtilis increased the average body weight(P < 0.05)of broilers at 42 days and the average daily weight gain(P < 0.01)during 22-42 days of broilers,and decreased the ratio of feed consumption to weight gain(P < 0.05),increased the average daily weight gain(P < 0.05)and the European benefit index(P < 0.05)of broilers at 1-42 days.Compared with NC group,bacitracin zinc significantly increased the average weight(P < 0.01)42 days,the average daily gain(P < 0.01)during 22-42 days and European benefit index(P < 0.05),and reduced the 1-42 days feed consumption to gain ratio(P< 0.05).Compared with PC group,Bacillus subtilis significantly reduced the 21 days average weight(P <0.01)and 1-21 days average daily gain(P < 0.01),and increased the 22-42 days average daily gain(P < 0.05).Compared with NC group,Bacillus subtilis and bacitracin zinc had no significant effect on dressed percentage、percentage of half-eviscerated yield、percentage of eviscerated yield、percentage of breast muscle、percentage of leg muscle、percentage of wings and percentage of abdominal fat(P > 0.05).Compared with NC group,Bacillus subtilis increased the b* value of meat color(P < 0.05),but had no significant effect on water holding capacity,L* and a* value of fleshcolor,tenderness and p H value(P >0.05).Bacitracin zinc had no significant effect on broiler meat quality(P > 0.05).There was no significant difference between bacitracin zinc and Bacillus subtilis on the meat quality of broilers(P > 0.05).(2)Compared with NC group,the supplementation of Bacillus subtilis and bacitracin zinc did not affect the content of Ig A,Ig G and Ig M in serum of broilers at d 42(P > 0.05).There was no significant difference in serum antioxidant status among Bacillus subtilis group,bacitracin zinc group and NC group(P > 0.05).Bacitracin zinc significantly reduced the activity of glutamine synthetase(GS)in liver(P <0.01).There was no significant difference in other liver antioxidant indexes among the three groups(P > 0.05).(3)Compared with NC group,Bacillus subtilis significantly reduced the depth of ileal crypt(P < 0.05),significantly increased the height of villi/depth of crypt ratio(VCR)(P < 0.05),but had no significant effect on the height of ileal villi(P > 0.05).There was no significant difference in villus height,crypt depth and villus height/crypt depth ratio(VCR)between three groups(P > 0.05).There was no significant difference between Bacillus subtilis group and bacitracin zinc group(P > 0.05).The results of 16 S r DNA showed that Bacillus subtilis increased the abundance of the bacteria related to the growth promoting performance,such as Flavonifractor,Blautia and Faecalibacterium in cecum.There was no significant difference in diversity ofα and β in cecum among the three groups(P > 0.05).PCo A cluster analysis showed that the species composition of bacitracin zinc group and Bacillus subtilis group were more similar.The correlation analysis of environmental factors showed that the abundance of Flavonifractor,Erysipelatocyclostridium,Hydrogenoanaearobacterium,Tyzzerella and Rikenella were related to body weight,average daily gain,European benefit index and villus height/crypt depth.In conclusion,Bacillus subtilis can improve the growth performance and meat color of broilers,but it has no effect on the slaughter performance and immune status;it has no effect on the antioxidant status of liver;it can improve villus height/crypt depth ratio,and the abundance of bacteria related to the growth performance,such as Flavifractor,Blautia and Faecalibacterium,was increased.