Epidemiological Investigation And Molecular Biological Analysis Of BVDV In Scale Dairy Farms In Parts Of Henan Province

Bovine viral diarrhea/Mucosal disease(BVD)is an infectious disease with multiple clinical symptoms caused by Bovine viral diarrhea Virus(BVDV).The disease not only has a complex pathogenic mechanism,but also lacks effective treatments.Bovine viral diarrhea has a direct impact on reproductive performance,milk production and has a significant economic impact on infected cattle herds.The significant economic impact of bovine viral diarrhea virus has prompted many countries around the world to implement regional or national eradication BVD program.In China,the rapid increase of BVDV infection also means that more cattle may be infected in the future,and the increase of virus genotypes means that prevention and control are more difficult.In this study,the epidemiological investigation and analysis of bovine viral diarrhea virus was conducted on dairy farms in Henan Province.The main findings are as follows:1.By sampling large-scale dairy farms in some areas of Henan Province,5486 serum samples collected were tested for BVDV antigen using the enzyme-linked immunosorbent assay method,and the regional location,scale,geographical location,age of dairy cows of different dairy farms were analyzed.analysis.The results showed that the average antigen positive rate was 1.77%(97/5486),and the field positive rate was 87.5%(35/40).Among them,the highest positive rate of BVDV in A10 dairy farms was 7.8%(11/141),and in A11 and A17 dairy farms,the lowest positive rate of BVDV was 0.66%(1/151).In different age groups,the highest positive rate of BVDV in heifers was 2.31%(21/910),and the lowest positive rate in calves was 1.12%(6/537).In different regional groups,in Zhumadian area,the highest BVDV antigen positive rate was 6.18%(18/291);in Hebi area,the lowest BVDV antigen positive rate was 0%(0/102).In the grouping of dairy farms of different scales,the positive rate of BVDV antigen was 2.78%(41/1472)in the pastures with a breeding scale of ≥1000 heads,and 1.39%(56/4014)in the pastures with a breeding scale of <1000 heads.In different geographical groups,the highest BVDV positive rate of dairy farms in southern Henan was 3.49%(27/774),and the lowest BVDV positive rate of dairy farms in eastern Henan was 1.16%(10/865).2.According to the BVDV antigen detection results,construct 5’-UTR and Npro gene primers from 96 antigen-positive samples for molecular biological analysis.The results showed that the primer amplification based on the 5’-UTR sequence could amplify a specific band of about 200 bp;the homology similarity between the 10 representative sequenced strains was 76.0%-100%,and the reference strains The homologous similarity between them was 69.0%-100%,and the 10 representative sequenced strains had four genotypes: BVDV-1d,1o,1m,and 1q.Primer amplification based on the Npro gene can amplify a specific band with a size of 429 bp;the homology similarity between the five representative sequenced strains is 65.4%~100%,and the homology similarity between the reference strains 61.9%~90.2%.The five representative sequenced strains have three genotypes: BVDV-1o,1m,and 1q.3.The protein rate,milk fat rate,somatic cell number,and daily milk yield of milk samples from 40 dairy farms were measured and counted to analyze the impact of BVDV infection on the production performance of dairy cows and the effects of BVDV in different parities,daily milk yield,Differences among milk fat percentage,protein percentage,and somatic cell count.The results showed that the daily milk yield of the 1st parity BVDV-positive cows increased significantly in the 5-25 kg stage,the 2nd parity BVDV-positive cows decreased significantly in the 25-40 kg stage,and the 3rd parity BVDV-positive cows were in the 5-25 kg stage.The daily milk yield was significantly reduced in the 25 kg stage;the protein rate of the 2-parity BVDV-positive cows was significantly increased in the ≥3% phase,and the protein rate of the 4-parity BVDV-positive cows was significantly decreased in the 2-3% phase.There were significant differences in BVDV seropositivity among different parities(P<0.05).