| Disease of avian embryo is a synthetical disease which is transmitted by eggs and is fatal to economy.This disease appeared on three parental generation branch farms of one large-scale AA broiler breeder farm(0.3million AA broiler breeder,6 branch farms),with the clinical manifestation of embryo death, increase of weak chicken ,decrease of incubation rate and inspritory symptoms in chicken, since March, 2005. The infection rate of E.coli and NDV increased, and the growth was stunted in 30day chicken, and this phenomenon didn't appear in other branch farms. So it was concluded that this disease was related to broiler breeder. To further study the cause of disease of avian embryo in this large-scale AA broiler breeder farm, epidemiological investigation,pathogenic studies and PCR to main pathogens were conducted, so suit measures could be taken for the prevention of disease of avian embryo in large-scale AA broiler breeder farm.The research including three parts:Part One: Pathogenic studies on the diseases of avian embryo in AA broiler breederA kind of disease appeared in one large-scale AA broiler breeder farm in Shandong province with the symptom of embryo death, increase of weakchicken, ineffective immunity, stunted growth of 30 days chicken since March 2005. Antibody in serum was tested to the broiler breeder, dead embryo ,1d chicken and the commercial chicken, it was showed that the average positive rate of ALV-J,CIAVwere 24.33 % and 5.00 %, respectively. The average positive rate of salmonella, mycoplasma, E.coli,bordetellaavium were 13.59%, 12.69%, 5.97%,19.62%and 6.72%, respectively. E.coli(36.00%),salmonella (24.73%), mycoplasma (19.52%), Bordetella avium(12.33%),ALV and CIAV were separatedfrom the organs of the death embryo, weak chicken and the commercial chicken by pathogenic study. It was showed that the co-infection of bordetella avium,salmonella, E.coli, mycoplasma, ALVand CIAV was the major cause of the disease. These pathogens spread vertically from the eggs to the embryos.Part Two:The molecular biological detection of the main pathogens of the immunosuppression-causing virusOnce the flocks are infected by the viruses, they will be susceptible to other viruses or pathogenic microorganism and the clinical symptoms caused by bacterial aren't typical. In addition, the immunosuppression-causing virus can make the antibody to the vaccines lower even cause immunization failure.With the result of part one,it was showed that ALVand CIAV were transmitted on this farm. In this part,the DNA and RNA were extracted from the organs of the death embryos, weak chickens and the commercial chickens .In order to find out whether the co-infection of immunosuppression-causing virus appeared or not, multiple PCR was conducted to CIAV, MDV,REV,ALV and the RT-PCR was conducted to IBDV and VAV. The positive rate of ALV-J and CIAV were 9.50% and 6.50%, it showed that the ALV and CIAV infections were the primary reason for the immunodepression of the flock.Part Three: Cloning and sequence analyses of capsid protein P27 gene of avian leukosis virus Subgroup JAvian leukosis virus Subgroup J(ALV-J)is a retrovirus that infects AA parental generation broiler breeders. ALV-J was first reported as a new subgroup of ALV by Payne in 1991.It can cause avian myelcytomatosis (ML)in broiler. ALV-J vas isolated and identified in 1999 from two broiler breeder farms with suspected lesions and 2 of 25 commercial broiler flocks by Prof. Cui Zhizhong's laboratory in China. Subsequently,more strains of ALV-J were identified in different lines of broiler.It was showed that the infection of bordetella avium(separated rate was24.33%)was the main cause of the disease of avian embryo in this large-scale AA broiler breeder farm by the pathogenic study. RNA was extracted from CEF cell infected with ALV-J(NXO101)and the gag-p27 gene was amplified by RT-PCR. Then the gene was cloned into plasmid pMD 18-T and sequenced. p27 Gene is 720 bp in length. Sequence comparison indicated thatthe nucleotide homolonv between the p27 gene and the reported sequence of NXO101 is 97.3 %. These results indicate the isolation from these broiler breeder flocks were ALV-J.
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