Epidemiological Investigation Of Major Bovine Respiratory Infectious Disease In Part Areas Of Ningxia Region

Bovine respiratory disease complex(BRDC)is a kind of bovine respiratory disease caused by the synergistic action of organism,pathogen and environment.It is one of the most serious diseases in cattle industry all over the world.BRD can cause fever,shortness of breath and cough in varying degrees,resulting in growth retardation of calves,decrease of milk yield of Iactating cows,abortion of pregnant cows and decline of sperm quality of bulls.It is generally believed that viruses are the primary pathogens of respiratory diseases,followed by or secondary infections of bacteria and other pathogens.In this study,ELISA and PCR or RT-PCR methods were used to detect the common pathogenic infections of bovine respiratory diseases from samples sent from four regions in Ningxia,and the related genes of the local epidemic strains were sequenced and analyzed by genetic evolution.The specific research results are as follows:1.Indirect ELISA was used to detect BRSV,BPIV-3 and M.bovis antibodies in 151 clinical bovine serum with respiratory symptoms.The results showed that the antibody-positive rates of the three pathogens were 75.5%,82.8%,and 70.2%,respectively.Among them,BRSV and M.bovis had the highest positive rate in Wuzhong area,83.3%and 80.3%,respectively;BPIV-3 had the highest positive rate in Zhongwei area,100%.The positive rates of BRSV and M.bovis were higher in winter;BPIV-3 was highest in autumn.The overall mixed positive rate of the three pathogenic antibodies was 84.1%,the double mixed positive rate was 35.1%,and the triple mixed positive rate was 49.0%.2.PCR or RT-PCR was used to detect BRSV,BVDV,BPIV-3 and M.bovis nucleic acid in 191 deep nasal swabs of clinically affected cattle.The results showed that the overall positive rates of the four pathogens were 61.8%,32.5%,46.6%and 24.6%.BRSV has the highest infection rate in Shizuishan area,69.0%;BVDV has the highest infection rate in Wuzhong area,35.0%;BPIV-3 and M.bovis have the highest infection rates in Zhongwei area,respectively 58.1%and 48.4%.BRSV,BVDV,and M.bovis are more common in winter,while BPIV-3 is more common in autumn.The overall mixed infection rate of the four pathogens was 52.8%,the double mixed infection rate was 34.0%,the triple mixed infection rate was 15.7%,and the quadruple mixed infection rate was 3.1%.3.Shown by gene sequencing and genetic evolution analysis,the N genes of the six BRSV sample strains were all closest to the A51908 strain in the United States.The 5’-UTR genes of the eight BVDV sample strains are all closest to the BVDV-1 type reference strain,belong to the BVDV-1 type.According to the genotyping method of BPIV-3,all six BPIV-3 sample strains belong to the BPIV-3a subtype.The oppD/F genes of 7 M.bovis samples were clustered with local isolates in China and the same small branch,and the genetic relationship was close,but the genetic relationship with the reference strains PG2 and 5632 of Mycoplasma lactis was far.In summary,the results of this study revealed the distribution and infection of the four pathogens BRSV,BPIV-3,BVDV and M.bovis in cattle in parts of Ningxia.It also clarifies the relationship and variation between its endemic strains and reference strains at home and abroad.It provides reference for Ningxia comprehensive prevention and control of bovine respiratory diseases,and also provides data support for further development of more effective vaccines.