| While antibiotic growth promoters bring rich benefits to the animal husbandry industry,there are also a lot of drawbacks.Nowadays,various countries have implemented the prohibition of antibiotics,so the search for safe and efficient antibiotic substitutes has become a research hotspot.In this experiment,the antibacterial activity,inhibition and killing effect of antibiotic substitutes(antibacterial peptide,acidifier and functional oligosaccharide)against Escherichia coli,Salmonella and Staphylococcus aureus were studied in vitro.Screening out products with better effects,taking white feathered broilers as the research object,the effect of combined supplementation of antimicrobial peptides,acidifiers and functional oligosaccharides to broilers’ diets instead of antibiotics on production performance,immune performance and intestinal function.In order to provide scientific basis and theoretical support for the popularization and application of green feed additives.In the first experiment,the inhibition and killing effect of antimicrobial peptides,acidifiers and functional oligosaccharides on Escherichia coli,Salmonella and Staphylococcus aureus were studied.Antibiotics(oxytetracycline calcium)were used as control.The inhibition zone was determined by oxford cup,and the minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)were determined by double dilution method.The results showed that antibacterial peptides,Acidifiers and functional oligosaccharides had antibacterial and bactericidal activities against Escherichia coli,Staphylococcus aureus and Salmonella.Antimicrobial peptide 4 and acidifier had antibacterial and bactericidal activities against Escherichia coli,Staphylococcus aureus and Salmonella.Functional oligosaccharide 1 had only inhibitory zone against the three pathogens,but no MIC and MBC.According to the results,antimicrobial peptide 4,acidifier and functional oligosaccharide 1 were selected as the next test samples for animal test.In the second experiment,the effect of combined supplementation of antimicrobial peptides(AP),Acidifiers(AC)and functional oligosaccharides(FOS)on growth performance,slaughter performance and nutrient metabolic rate of broilers were studied.A total of 720 one-day-old broilers(Arbor Acres)were randomly divided into 6 groups with 6 replicates in each group and 20 chickens in each replicate.Broilers in the control(NC)group were fed with basal diet,and the antibiotic(AN)group were fed with basal diet supplemented with 500 mg/kg oxytetracycline calcium(based on 50 mg/kg oxytetracycline active ingredient),and the others in experimental groups were fed with the basal diets supplemented with 300 mg/kg antimicrobial peptide and 200 mg/kg functional oligosaccharide(AP+FOS group),300 mg/kg antimicrobial peptide and 350 mg/kg acidifier(AP+AC group),350 mg/kg acidifier and 200 mg/kg functional oligosaccharide(AC+FOS group)and 300 mg/kg antimicrobial peptide,350 mg/kg acidifier and 200 mg/kg functional oligosaccharide(AP+AC+FOS group).The experiment lasted for 42 days.The results showed as follows:1)Compared with the NC group,the average daily gain(ADG)in AN,AP+FOS,AP+AC,AC+FOS,and AP+AC+FOS groups were significantly increased at the age of 22 to 42 days and 1 to 42 days(P<0.05),while the F/G were significantly decreased at the age of 22 to 42 days and 1 to 42 days(P<0.05),and the body weight(BW)were significantly increased at the age of 42 days(P<0.05),the feed/gain(F/G)in AP+FOS group was significantly decreased at the age of 1 to 21 days(P<0.05).Compared with AN group,there was no significant difference in ADG,ADFI and F/G among AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups in each period(P>0.05).2)Compared with NC group,the breast muscle rate of of 42-day-old broilers in AN,AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups were significantly increased(P<0.05),and the abdominal fat rate was significantly decreased(P<0.05).Compared with the AN group,there were no significant differences in chest muscle rate and abdominal fat rate of 42-day-old broilers in AP+FOS,AP+AC,AC+FOS,AP+AC+FOS groups(P>0.05).There was no significant difference in dressing percentage,half-bore rate and full bore rate of 42-day-old broilers among the experimental groups(P>0.05).3)Compared with NC group,the metabolic rate of crude protein and phosphorus of 42-day-old broilers in AP+FOS,AP+AC,AC+FOS,AP+AC+FOS groups were significantly increased(P<0.05),the metabolic rate of ether extract in AC+FOS group was significantly increased(P<0.05).Compared with AN group,the metabolic rate of crude protein,crude fat,calcium and phosphorus of 42-day-old broilers in AP+FOS,AP+AC,AC+FOS,AP+AC+FOS groups had no significant difference(P>0.05).In the third experiment,the effect of combined supplementation of antimicrobial peptides(AP),Acidifiers(AC)and functional oligosaccharides(FOS)on immune organ index,serum immune index and expression of inflammatory immune factors in intestinal mucosa of 42-day-old broilers were studied.The experimental animals and design were the same as the second experiment.The results showed as follows:1)Compared with NC group,the indexes of thymus,spleen and bursa of fabricius in AP+FOS,AP+AC,AC+FOS,AP+AC+FOS groups were increased,but the difference was not significant(P>0.05).2)Compared with NC and AN groups,the content of immunoglobulin A(IgA)in AP+FOS,AP+AC and AP+AC+FOS groups increased significantly(P<0.05),and the content of immunoglobulin G(IgG)in AP+FOS,AP+AC and AC+FOS groups increased significantly(P<0.05).Compared with NC group,the content of immunoglobulin M(IgM)in AN,AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups increased significantly(P<0.05).3)Compared with NC group,the mRNA expression levels of IL-2,TNF-α and IFN-y in jejunum and ileum of AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups were significantly decreased(P<0.05),and the mRNA expression levels of IL-4 in jejunum were significantly increased(P<0.05).In the fourth experiment,the effect of combined supplementation of antimicrobial peptides(AP),Acidifiers(AC)and functional oligosaccharides(FOS)on intestinal pH,intestinal morphology and caecum microbial flora of 42-day-old broilers were studied.The experimental animals and design were the same as the second experiment.The results showed as follows:1)Compared with NC group,the pH values of jejunum in AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups were significantly lower(P<0.05).Compared with AN group,the pH value of duodenum,ileum and cecum in AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups were not significantly different(P>0.05).2)Compared with NC group,the crypt depth of duodenum and ileum in AN,AP+FOS,AP+AC AC+FOS and AP+AC+FOS groups decreased significantly(P<0.05),the duodenum V/C in AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups increased significantly(P<0.05),and the ileum V/C in AP+FOS,AP+AC and AP+AC+FOS groups increased significantly(P<0.05).3)Compared with NC and AN groups,the Ace index,Chaol index and Shannon index of AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups increased to some extent.Compared with NC group,the relative abundance of Ruminococcaceae UCG-014 and Synergistes in AP+FOS,AP+AC,AC+FOS and AP+AC+FOS groups increased.In conclusion,combined supplementation of antimicrobial peptides,acidifiers and functional oligosaccharides can improve the growth performance and immune performance of broilers,ameliorate slaughter performance,nutrient metabolic rate,the morphology and pH of small intestine,regulate the diversity and abundance of cecal microorganisms,and the intestinal health of the broilers is promoted.The growth performance of the three combinations was not better than that of the two combinations.The combination of antimicrobial peptides with acidifiers and functional oligosaccharides has a better effect on immune performance.It is recommended that antimicrobial peptides,acidifiers and functional oligosaccharides can be supplemented in pairwise combination to achieve the effect of adding antibiotics,which has the potential to replace antibiotics. |
