Epidemiological Investigation On The Causes Of Mortality Of White Feather Broiler Chicks In Shandong And Surrounding Areas During The Brooding Period

In recent years,with the continuous expansion of white-finned broiler breeding,the incidence of many infectious diseases has become higher and higher,and the phenomenon of high mortality of chicks exists in many commercial broiler farms.As the immune organs of chicks are not yet fully developed and the immune function is not yet perfect,they are very easy to be infected with various epidemics,resulting in increased morbidity and mortality of commercial broilers in the pre-feeding process,which has a greater impact on the economic benefits of broiler rearing.To understand the causes of white feather broiler chick mortality during the brooding period in Shandong Province and surrounding areas,411 samples of clinically dead chicks were collected from 14 large-scale commercial broiler farms in Shandong Province and surrounding areas between June 2021 and June 2022 in this study.Epidemiological investigations were conducted on the common pathogens of H9-Avian Influenza virus,Avian leukemia virus subtype J,Avian reovirus infection,Chicken infectious anemia virus,Fowl adenovirus,Mycoplasma,Escherichia coli,Salmonella and Staphylococcus during the brooding period.To provide epidemiological information to ensure the healthy and stable development of white feather broiler farming in Shandong Province and surrounding areas.In this study,seven pairs of specific detection primers were designed and synthesized according to the base sequences of HA gene of H9-AIV,gp85 gene of ALV-J,σC gene of ARV,VP1 gene of CIAV,hexon gene of FAd V,and some genes of Mycoplasma Galliscepticum and Mycoplasma Synoviae in Gen Bank.The collected samples were tested for nucleic acids,with H9-AIV,ARV,ALV-J,MG and MS detected by RNA extraction for RT-PCR assay;FAd V and CIAV were detected by DNA extraction for PCR.The test results showed that the positive rates of H9-AIV,ARV,FAd V,ALV-J,and CIAV were 19.71%(81/411),13.38%(55/411),11.19%(46/411),4.62%(19/411),and 3.89%(16/411),respectively;the positive rates of MG and MS were 3.41%(14/411)and 5.11%(21/411),respectively.The above results indicated that H9-AIV infection rate was the highest,followed by ARV and FAd V,and ALV-J,CIAV and Mycoplasma were less prevalent.The statistical results of viral diseases in different seasons showed that dead chicks had the highest viral positivity in winter and spring,followed by autumn and the lowest in summer.A total of 14 strains of H9-AIV,12 strains of ARV,10 strains of FAd V and 4 strains of ALV-J were isolated and cultured from the typical disease material identified as positive by PCR.The genetic evolutionary analysis of viral gene sequences was performed by PCR/RTPCR tests for identification and sequencing,and by comparison with standard strains by Megalign and MEGA6 software,and the results showed that H9-AIV,ARV,FAd V and ALVJ all had some variation.All 14 H9-AIV strains belonged to the h9.4.2.5 branch;the proportion of genotype 1,2,4 and 5 among the 12 ARV strains was 50%(6/12),8.33%(1/12),8.33%(1/12)and 33.3%(4/12),respectively,indicating that genotype 1 and 5 were the predominant prevalent strains;The percentages of serotypes 1,4,8a and 8b among the 10 FAd V strains were10%(1/10),40%(4/10),10%(1/10)and 40%(4/10),respectively,indicating that serotypes 4and 8b were the predominant prevalent strains.Isolation and identification,biochemical characterization and drug resistance testing of Escherichia coli,Salmonella and Staphylococcus were performed on the diseased and dead chicks with suspected bacterial infection in the collected samples.The results showed that the positive rates of E.coli,Salmonella and Staphylococcus were 12.65%(52/411),4.86%(20/411)and 0.97%(4/411),respectively.The biochemical test results showed that the isolated strains were consistent with the biochemical characteristics of the corresponding E.coli,Salmonella and Staphylococcus.Drug susceptibility results showed that the isolated E.coli had higher susceptibility to bindamycin,ofloxacin,minocycline and polymyxin B,and higher resistance to erythromycin,lincomycin,penicillin and amoxicillin;High susceptibility of isolated Salmonella to gentamicin,enrofloxacin,butamycin,florfenicol,ciprofloxacin and high resistance to erythromycin,amoxicillin,penicillin,streptomycin and lincomycin;The isolated staphylococci were more susceptible to ciprofloxacin,minocycline,cefotaxime,and cefradine,and more resistant to erythromycin,florfenicol,streptomycin,penicillin,and lincomycin.Bacterial disease statistics for different seasons showed that dead chicks had the highest bacterial positivity in summer,followed by viral positivity in winter and autumn,and the lowest in spring.In summary,the highest positive rates of H9-AIV,ARV,FAd V and E.coli were detected in white feather broiler chicks during the brooding period in Shandong and surrounding areas,which are the main causes of early mortality in white feather broilers.Therefore,it is important to strengthen the prevention and control of related viral and bacterial infectious diseases for the development of white-finned broiler farming.