Epidemiological Investigation And Suggestions On Prevention Control Of BVD In Two Scale Cattle Farm In Northern Xinjiang

Bovine viral diarrhea disease(BVD)has been found in China for more than 30 years and has been studied for more than 70 years worldwide.Because bovine viral diarrhea virus(BVDV)can infect pregnant cows in the second trimester of pregnancy through placenta,resulting in abortion,stillbirth or calf birth but death under age.If calves survive,it will produce "immune tolerance" to the virus,which translates into persistent infection(PI)cows,carrying and detoxifying for life,with a daily detoxification capacity of 1-10 million,so PI cattle.It is an important source of infection of the disease.Although the mortality rate caused by this disease is low,it will reduce the autoimmunity of cattle,which will make cattle more susceptible to other diseases,such as mastitis,foot-and-mouth disease,infectious bovine rhinotracheitis and so on.Therefore,it is necessary to continuously purify the PI cattle that may exist in cattle farms.In order to understand the epidemiological situation of BVD in two large-scale cattle farms in northern Xinjiang,the whole blood and serum samples of cattle in two large-scale cattle farms were collected,detected and eliminated,and the serum of PI cattle was isolated and identified.BVDV antigen detection and re-examination were carried out on 3856 cattle in immunized A farm and 454 cattle in non-immunized B farm.The results showed that the positive rates of antigen were 0.18%(7/3856)and 2.6%(12/454)in immunized A farm and 0.05%(2/3856)and 1.76%(8/454)in re-examined PI cattle in two farms after three weeks.The BVDV antigen of two PI cows in A cattle farm was further tested,and the results were negative.RT-PCR was negative for frozen semen from two cattle farms.Viruses were isolated by cell culture and identified by RT-PCR.A 294 bp 5-’UTR partial sequence and a 524 bp Nopro partial sequence were amplified.The genetic evolution tree of the isolated strain was drawn by MEGA7.0.The genotype of the isolated strain was determined.The results showed that XJ11A belonged to BVDV-lc subtype and XJ45B belonged to BVDV-1f subtype.This study showed that BVDV persistent infection existed in cattle farms in northern Xinjiang,and the epidemic subtypes were different.In view of the actual feeding and environmental conditions of the two cattle farms,the elimination and harmless treatment of PI positive cattle were adopted,and comprehensive prevention and control were carried out while eliminating PI cattle.The purpose of controlling BVD in cattle farms was achieved,which provided reference for the control and purification of BVD in other cattle farms.