The Epidemiological Investigation And Immune Prevention And Control Technology Promotion Of Porcine Reproductive And Respiratory Syndrome Of Large-scale Pig Farms In Guiyang

Porcine reproductive and respiratory syndrome(PRRS)is caused by porcinereproductive and respiratory syndrome virus(PRRSV)and can lead to serious reproductive barriers in sows and respiratory symptoms in weaned pigs.At present,PRRS is one of the most severe viral diseases that cause great economic losses to the pig industry,which has spread all over the world.According to incomplete statistics,the direct and indirect economic losses caused by PRRS have reached more than 40 billion and 100 billion,respectively.In recent years,the implement of animal immunization and risk ability evaluation is the most important methods to prevent and control the animal infectious diseases.There are many measures,such as the immune effect analysis,epidemic disease diagnostic techniques,risk prevention and control,the integration of qualitative and quantitative analysis and so on,are continually proceeded to make the evaluation results more scientific and feasible.Although lots of works have been made to promote the immune effect,the otherness in territory and the variation in viruses give rise to the failure of immunization.More reasonable evaluation methods should be formulated to use in large-scale farms.Therefore,five aspects of research works were carried out to solve the frequent occurrence of PRRS in Guiyang region in this study.1.The epidemiological investigation of PRRS of large-scale pig farms in Guiyang region.Large-scale pig farms in Guiyang including Huaxi district,Kaiyang county,Wudang district were investigated to understand the epidemiologic feature of PRRS from 2012 to 2014.In addition,the morbidity and prevalence state of PRRS in sows were especially collected and analyzed.The results showed that the epidemiologic feature of PRRS in Guiyang showed seasonal epidemic,mainly in June to August.The highest morbidity was in Yorkshire swine,and the lowest was in black pigs,which mainly distributed in Huaxi district,Kaiyang county and Wudang district.2.The evaluation of immune level of PRRS in large-scale pig farm in Guiyang.2880 serum samples from different PRRS vaccines and immune procedures were collected from 40 different large-scale pig farms in Guiyang from 2012 to 2014.The ELISA assay was used to detect the immune level of PRRS.The results showed that the antibody positive rate of PRRSV increased year by year in recent three years.The antibody level of secondary immune was much higher than the first immune.The average positive rate of antibody level inoculated with PRRS live vaccine was superior to PRRS inactivated vaccine.3.The immune effect detection of PRRS vaccine in experimental pig farms.Four pig farms were chose to investigate the production status,epidemiological history of PRRS,immune effect of PRRS vaccine and so on.On the other hand,the antibody levels of 982 serum samples from sows,sucking pigs and child pigs were detected by ELISA.The results showed that the PRRSV antibody level of sows in the four pigs farms was higher than that of sucking pigs and child pigs,but the antibody positive rate was different among the four pig farms.Meanwhile,two of them were found to be suspected infection with PRRSV.Through this investigation,we found that these pig farms existed in some problems such as the unreasonable immune procedure and immune method,the insecurity of breeding environment,the lack of favorable feeding and management styles.4.Isolation and characterization of PRRSV from large-scale pig farms.A pair of specific primers used to amplify PRRSV GP5 gene were designed according to the GP5 gene sequences of LV,VR-2332 and CH-1a strains.Tissue samples collected from clinical suspected PRRSV infection were disposed and then inoculated to Marc-145 cells.The complete RNA genomes of the isolated viruses were extracted using Trizol method,and the GP5 genes were amplified by RT-PCR and then sequenced by direct sequencing.Sequence analysis showed that two isolates belonged to North American genotype PRRSV and had the same branch as CH-1a strain,which provided fundamental work for researching and controlling the PRRS in large-scale pig farm.5.PRRS immune adjustment and application of PRRS prevention and control technology in large-scale pig farms.A set of measures were planned for the prevention and control of PRRS in Guiyang region,according to the research results of one to four chapter.The application of this measure in five experimental pig farms showed that the antibody positive rate of five pig farms all reached 90 percent,and the morbidity and mortality were obviously decreased,indicating that the early warning evaluation index of PRRS antibody level and immune assessment model were successfully created.The successful application of this measure to large-scale pig farms will provide a good theoretical basis for the prevention and control of PRRS in Guiyang region.