Protective Effect Of Antimicrobial Peptides On Broilers Infected With Salmonella Typhimurium

Salmonella typhimurium is a gram-negative facultative anaerobic bacterium,which can cause diarrhea and death of young birds,adult birds can also carry bacteria for a long time,causing serious economic damage to farms and a serious threat to public health safety.Since January 1,2020,China banned the addition of antibiotics to feed,the incidence rate of bacteria in poultry production has also increased.Especially Salmonella is one of the main pathogens of poultry,and its incidence rate has increased.Therefore,the use of new antibiotic substitutes to control Salmonella infection is the development trend in the future.Antimicrobial peptide is a kind of polypeptide widely existing in microorganisms,animals,plants and human body.It has become a good substitute for antibiotics because of its green,healthy and drug-free characteristics.The antibacterial peptide used in this experiment comes from hyalophora cecropia,and its main component is cecropins.It has good ability to resist Gram-negative pathogens.Previous in vitro experiments show that the antibacterial peptide in this experiment can effectively inhibit the activity of Salmonella and Escherichia coli,but the protective effect of cecropin on Salmonella typhimurium infection in broilers is lack of systematic research.The purpose of this experiment was to study the effects of antimicrobial peptides on the growth performance,pathological changes,serum and intestinal related immunoglobulins and related inflammatory factors of broilers infected with Salmonella typhimurium.In this experiment,240 1-day-old Hongyu 380 broilers were randomly divided into 4 groups（3replicates in each group and 20 chickens in each replicate）.The specific groups were as follows:Group x was the control group（basic diet + Salmonella typhimurium challenge）,group 1 was the low-dose antimicrobial peptide group（basic diet + 500 g / T antimicrobial peptide preparation + Salmonella typhimurium challenge）,and group 2 was the medium-dose antimicrobial peptide group（basic diet + 1000 g / T antimicrobial peptide preparation +Salmonella typhimurium challenge）,The three groups were high-dose antimicrobial peptide group（basic diet + 1500 g / T antimicrobial peptide preparation + Salmonella typhimurium challenge）;The trial period was 28 days,and routine immunization was carried out in the whole process.The results are as follows:1.Growth performance: at 14,21 and 28 days of age,the body weight of group 2 and 3was significantly higher than that of group x（P < 0.01）,the body weight of group 1 was significantly higher than that of group x at 14 days of age（P < 0.01）,and there was no significant difference between group 1 and group x after 14 days of age（P > 0.05）;2.The average daily gain of group 3 was significantly higher than that of group x（P < 0.01）,the material weight ratio of group 2 and 3 was significantly lower than that of group x（P < 0.01）,and the average daily gain and material weight ratio of group 1 were not significantly different from that of group x（P > 0.05）.The results showed that the medium and high dose groups could significantly improve the growth performance of infected broilers.2.Pathological changes: through autopsy,it was found that the intestinal lesions in group x were mainly diffuse hemorrhage and necrosis,there were a large number of necrotic spots in the liver and a large number of necrotic granulomas in the heart in the later stage,and the intestinal lesions in antibacterial peptide group were mainly a small number of bleeding spots and bleeding spots;Necrosis and necrotic granuloma appeared in a small amount of chicken liver and heart in groups 1 and 2,while the liver and heart lesions in group 3 were not very obvious.Through the lesion score,it can be found that the score of the antibacterial peptide group is significantly lower than that of the control group,and the score of the high-dose group is the lowest.3.Detection of serum associated immunoglobulin: the contents of Ig M and Ig A in serum of antimicrobial peptide group from 14 to 28 days old were significantly higher than those in group x（P < 0.01）;After 21 days of age,the content of serum Ig G in groups 2 and 3 was significantly higher than that in group x（P < 0.01）,and there was no significant difference between group 1 and group x（P > 0.05）.It shows that the medium and high dose groups can significantly increase the antibody level in the serum of infected broilers.4.Detection of relevant inflammatory factors in serum: There was no significant difference in serum IL-6 before 21 days of age（P > 0.05）.After 21 days of age,the content of serum IL-6 in groups 2 and 3 was significantly higher than that in group x（P < 0.01）;There was no significant difference in serum IL-10 before 28 days of age（P > 0.05）.After 28 days of age,the content of serum IL-10 in group 2 was significantly higher than that in group x（P < 0.05）,and the content of serum IL-10 in group 3 was significantly higher than that in group x（P < 0.01）.It shows that the medium and high dose groups could significantly increase the contents of IL-6 and IL-10 in serum of infected broilers.5.Detection of intestinal associated immunoglobulin and barrier function: the content of intestinal s Ig A in antibacterial peptide group after 14 days was significantly higher than that in group x（P < 0.01）,and the content of intestinal ZO-1 in antibacterial peptide group after 14 days was significantly higher than that in group x（P < 0.01）.It shows that the medium and high dose groups can significantly improve the intestinal immune ability of infected broilers.In conclusion,the addition of 1000 g / T or 1500 g / T antimicrobial peptides in the feed can significantly improve the production performance of broilers infected with Salmonella typhimurium,reduce the degree of pathological changes of broilers infected with Salmonella typhimurium,improve the immune ability of broilers infected with Salmonella typhimurium,and play a good role in the prevention and treatment of broilers infected with Salmonella typhimurium.