Effect Of Phage Cocktail On Growth Performance Of Broilers

Avian pathogenic Escherichia coli and avian Salmonella are common pathogens in poultry breeding,causing huge losses to my country’s animal husbandry.At present,antibiotics are often used to treat these two diseases,but the irregular application of antibiotics has led to the increase of drug-resistant bacteria,environmental pollution,and threats to human health.With the implementation of the policy of reducing antibiotic resistance and limiting antibiotic resistance,the aquaculture industry has an increasingly urgent demand for antibiotic alternatives.Bacteriophage has the advantages of efficient sterilization,safety,and no pollution,and is an ideal drug and feed additive for the prevention and treatment of bacterial diseases.In this study,5 strains of avian Salmonella phages and 7 strains of avian coliform bacteriophages isolated in the laboratory were recovered,their biological characteristics were determined,and a phage cocktail was prepared.In this study,the effects of drinking water phage cocktail on broiler chicken growth performance and intestinal health were verified in large chicken farms,and compared with the effect of normal feeding antibiotics.It provides a new idea for clinical prevention and treatment of poultry colibacillosis and poultry salmonosis,and provides theoretical support for its use as a new type of feed additive.The specific results are as follows:1.Phage recovery,purification and determination of biological properties7 strains of Escherichia coli phage,5 strains of Salmonella phage and their host bacteria were recovered,and purified after proliferation.The best multiplicity of infection of 12 strains of phage was determined.The results of thermostability assay showed that the titers of 12 phages remained unchanged at 40℃and 50℃;when the temperature increased to 70℃,the phage survival rate dropped sharply.The results showed that the 12 strains of phage could maintain a high survival rate at room temperature,but were not resistant to high temperature.The results of pH stability assay showed that the 12 phages could maintain high activity at pH 4-11,but the phage activity decreased sharply when pH<3 or pH>11.The results showed that the 12 phages could maintain stable activity at pH 4-11,but were not resistant to strong acid and alkali.2.Phage Cocktail Preparation and Lysis ProfilingThe phage cocktail was prepared,and the total titer of the phage cocktail was 5×10~8PFU/m L.Determination of lysis profile:The total lysis rate of phage cocktail to 256 avian Salmonella strains from Hubei reached 96.09%(246/256);the total lysis rate to 743 avian pathogenic Escherichia coli strains from Hubei reached 97.98%(728/743).3.Research on the Application of Phage Cocktails42,400 28-day-old broilers were randomly divided into 2 groups(phage group and antibiotic group).The results are as follows:The effect of phage cocktail on growth performance:Compared with the antibiotic group,the average daily weight gain of the phage group was 1.1%higher than that of the antibiotic group(P>0.05);the average daily feed intake was reduced by 5.75 g(6.3%),and the feed-to-weight ratio was significantly lower 9.7%(P<0.05).The results showed that the phage cocktail could significantly reduce the feed to meat ratio in broilers compared to antibiotics.The effect of phage cocktail on intestinal structure and intestinal barrier:Compared with the antibiotic group,the villus height in the phage group was significantly increased by 9.1%(P<0.01),and the VH/CD value was significantly increased by 6.5%(P<0.01).Crypt depth had no significant effect(P>0.05);the expression levels of ZO-1 and Claudin-1 in jejunum of broiler chickens were significantly increased(P<0.05);the expression levels of Occludin had no significant difference(P>0.05);jejunal mucin MUC-The expression level of 2 was significantly increased(P<0.05).The results showed that compared with antibiotics,the phage cocktail could significantly improve the intestinal tissue morphology of broiler chickens,and significantly improve the intestinal physical barrier and intestinal chemical barrier of broiler chickens.The effect of phage cocktail on intestinal inflammatory factors:Compared with the antibiotic group,the phage cocktail had no effect on the expressions of IL-1β,IL-6 and TNF-αin the intestine(P>0.05).The effect of phage cocktail on intestinal flora:Compared with the antibiotic group,the amount of Escherichia coli and Salmonella in the phage group was not significantly different(P>0.05),and the abundance of Lactobacillus was significantly increased(P<0.05).It shows that the phage cocktail can increase the abundance of Lactobacillus in the intestine compared with antibiotics,and at the same time has the same effect of killing pathogenic bacteria as antibiotics.In summary:Compared with antibiotics,the phage cocktail can improve the intestinal mucosal structure,enhance the physical and chemical barriers of the broiler intestine,reduce the intestinal pathogenic bacteria,increase the content of beneficial bacteria such as Lactobacillus in the intestine,and promote the intestinal flora.Balance and other effects can increase the average daily weight gain of broilers,reduce the feed-to-meat ratio,and improve the growth performance of broilers.Studies have shown that phage cocktails are one of the effective options to replace antibiotic products.