Study On Effect Of Dietary Supplementation With Bacillus Subtilis ATCC19659 On Growth Performance, Immune Function, And Intestinal Health Of Broilers

Broiler production is one of the important components of agricultural production,characterized by short growth cycles,low production costs,and clear economic benefits.Chicken has the characteristics of low-fat content,delicious taste,and rich nutrition.Eating chicken can help reduce the nutritional gap in the world.In poultry production,feed accounts for approximately 70%of the total cost of intensification.Feed additives have important significance in the health care systems.Using antibiotics in broiler diets can resist poultry pathogens and improve growth performance,but excessive use of antibiotics can cause problems such as drug residues and drug resistance.Bacillus subtilis can form spores,has strong resistance,and can promote the growth and health of broilers.It is one of the common probiotics used as feed additives.Bacillus Subtilis ATCC19659（BST-ATCC19659）is a newly introduced probiotic.Due to its unclear probiotic effects on broilers,this paper conducted two broiler feeding experiments with Arbor Acres（AA）broilers to investigate the effects of dietary supplementation of BST-ATCC19659 on growth performance,immune function,and intestinal health of broilers,and further explore the optimal dosage and probiotic mechanism.Experiment 1 investigated the effects of dietary supplementation with BST-ATCC19659 on growth performance,organ index,liver function,and kidney function in broilers to evaluate the feasibility of using BST-ATCC19659 in broilers.In the experiment,600 1-day-old AA broilers were randomly divided into 5 treatments:（1）the control group was fed with a basic diet（CONT）;（2）Adding 500 mg/kg zinc bacitracin to the basic diet（Znb T）;（3）Basal diet Addition 1×10⁸ CFU/g BS-ATCC 19659 diet（BST-1）;（4）Basal diet Addition 3×10⁸CFU/g BST-ATCC 19659（BST-3）;（5）Basal diet Addition 5×10⁸ CFU/g BST-ATCC19659（BST-5）.Each treatment had 6replicates/cages,and 20 chickens per cage.The trial period was 42 days.The results showed that there was no significant difference in the growth performance and relative organ wight of broilers among the 5 groups fed on day 42（P>0.05）,and there was no abnormality in the organs of each experimental group during the entire feeding period.The bursa of Fabricius broilers fed on day 21,BST-3 group was heavier than that of the CONT group（P<0.05）.There was no significant difference in the bursa of Fabricius broilers among BST-1,BST-5,and CONT groups,while there was no significant difference in the other organ indexes of among 5 groups（P>0.05）.At day 42,the jejunal content p H of broilers fed with Znb T,BST-1,BST-3,and BST-5 was higher than that of CONT,while there were no significantly difference in the jejunal content p H of broilers fed with Znb T,BST-1,BST-3,and BST-5.After feeding for 21^st and 42^nddays,the total protein（TP）,albumin（ALB）,and high-density lipoprotein（HDL）of broilers in the BST-5 and Znb T groups were higher than those in the CONT,BST-1,and BST-3 groups（P<0.05）.After 21 days of feeding,the levels of low-density lipoprotein（LDL）,very low-density lipoprotein（VLDL）,and triglycerides（TG）in the BST-1,BST-3,BST-5,and Znb T groups were lower than those in the CONT group（P<0.05）.After 42 days of feeding,the LDL,VLDL,TG,and total cholesterol of broilers in the BST-1,BST-3,BST-5 and Znb T groups were lower than those in the CONT group（P<0.05）.After feeding for 21 and 42 days,there were no abnormalities in liver and kidney functions in each experimental group during the entire feeding period.After 21 days of feeding,the levels of creatine and uric acid in the BST-1,BST-3,BST-5,and Znb T groups were lower than those in the CONT group.After 42 days of feeding,the creatine and uric acid levels in the BST-5 and Znb T groups were lower than those in the CONT and BST-1 groups.Experiment 2 investigated the effects of dietary supplementation with BST-ATCC19659 on growth performance,antioxidant function,intestinal morphology,immune function,and microbial flora in broilers to explore the optimal dosage and probiotic mechanism of BST-ATCC19659.In the experiment,600 1-day-old AA broilers were randomly divided into 5 treatments:（1）the control group was fed with a basic diet（CONT）;（2）Adding 500 mg/kg zinc bacitracin to the basic diet（Znb T）;（3）base diet addition 1×10⁸CFU/g BST-ATCC19659 into diets（BST-1）;（4）basal diet addition 3×10⁸CFU/g BST-ATCC19659 into diets（BST-3）;（5）basal diet addition 5×10⁸ CFU/g BST-ATCC19659 into diets（BST-5）.Each treatment had 6 replicates/cages,and 20 chickens per cage.The trial period was 42 days.The results showed that the bodyweight and average daily weight gain of the BST-5 group on day 21 were higher than those of the CONT and Znb T groups（P<0.05）.The end weight of the BST-3 and BST-5 groups on day 42 was higher than those of the CONT and Znb T groups,but there was an upward trend compared to the CONT and Znb T groups,but there was no significant difference in the rest of indictors（P<0.05）.After 21 and 42 days of feeding,the serum levels of glutathione peroxidase（GSH）,total antioxidant capacity（T-AOC）,catalase（CAT）,and superoxide dismutase（SOD）in the BST-5,BST-3,and Znb T groups were higher than those in the CONT group（P<0.05）;The content of serum malondialdehyde（MDA）in the BST-5 group and the Znb T group were lower than those in the CONT,BST-1,and BST-3 groups（P<0.05）.After 21 and 42 days of feeding,serum concentrations of immunoglobulins（Ig G,Ig E,Ig M,Ig A）,secretory immunoglobulins（SIg A）,and complement components（C3,C4）in the Znb T,BST-1,BST-3,and BST-5 groups were higher than those in the CONT group（P<0.05）.Serum anti-inflammatory cytokine TGF-βand IL-10 of broilers in Znb T,BST-3,BST-5,and on day 21 and 42 were higher in the CONT group（P<0.05）.Broilers fed day 21 and day42,serum proinflammatory cytokine TNF-α,L-6 and IL-4 concentrations in Znb T,BST-3,and BST-5 groups were lower than in the CONT group（P<0.05）.The liver tissue GHR,CAT,IGF-1,SOD,IFN-γ,TGF-βm RNA levels of broilers fed with day42,BST-3,and BST-5 groups were higher in the CONT and Znb T groups（P<0.05）.The ileal villus height in the BST-3 and Znb T groups was higher than that in the CONT group（P<0.05）;The ileal villus height/crypt depth ratio in the Znb T,BST-5,and BST-3 groups were higher than that in the CONT group（P<0.05）.The abundance of Cyanobacteria phylum in the cecal community was significantly decreased in the BST-1and Znb T groups when compared to the CONT group（P<0.05）.At the family level,the proportions of Peptococcaceae and Clostridiaceae families were significantly a higher in the Znb T and BST-5（P<0.05）.The abundance of Enterobacteriaceae family was significantly lower in the BST-3 group than in the CONT group（P<0.05）.The abundance of Rhodospirillales＿unclassified family was increased significantly in the BST-1 group（P<0.05）.At the genus level,the proportions of Papillibacter and GCA-900066575（Lachnospiraceae）genus（Firmicutes phylum）in the cecal community were significantly increased in the Znb T and the BST-ATCC19659 groups when compared to the CONT group（P<0.05）.The abundance of Escherichia-Shigella genus was significantly decreased in the BST-3 group（P<0.05）.Compared to the CONT group,the abundance of Clostridia＿unclassified genus was significantly decreased in the Znb T and BST-5 groups in the cecal microbiota of broilers（P<0.05）.Based on the above research results,adding BST-ATCC19659 to the diet has no adverse effects on broilers.It can improve the growth performance and intestinal health of broilers by improving their immune and antioxidant functions,improving their intestinal microflora.Combining all test indicators,dietary supplementation 5×10⁸CFU/g BST-ATCC 19659 is the best,and BST-ATCC19659 can be used as an antibiotic substitute in meat and poultry feed.