Detection And Analysis Of Antibodies Against Porcine Reproductive And Respiratory Syndrome Virus In A Large Scale Pig Farm Of

Porcine reproductive and respiratory syndrome(PRRS) is a great danger to swine industry. In July 2014, the clinical symptoms, such as sow abortion, stillbirth and increasednursery pig mortality, rapid breath, increased body temperature, decreased appetite, hemorrhage, congestion and purple color in ears of individual pigs were found in a large scale pig farm of Western Henan. Then, PRRS in the farm were investigated. The attenuated PRRSV vaccine was used to immunize the swine herds. The seral antibodies against PRRSV were detected and analyzed. The best immunization program was searched in order to provide the technical support to PRRSV infection control in the farm.Before vaccination, a total of 140 sows and boars were randomly selected for antibody detection, and the antibody positive rate reached 22.14%. Thirty five pregnant sows without detectable antibodies were selected, and immunized 7 d, 30 d, 5 d, 7 d and 90 d, respectively, afterpregnancy. The detection of PRRSV antibodies was conducted 7 d, 21 d, 28 d, 56 d, 84 d and 110 d, respectively, after immunization. The results showed that high antibodylevels remained at 21 d to 84 d after immunization, and the protective effect of antibody was still maintained 110 d after immunization.The sows without detectable antibodies were selected and divided into 8 groups for immunization after atdifferent time. 3 sows were chosen in each group. After delivery, six piglets were randomly selected for detection of PRRSV maternal antibodiesin 14 days of age. The results showed that when sows were immunized duringthe pregnancyof 36 d-110 d, piglets at 14 d had higherantibody levels.However,when the sows were immunized 50 d ago or 80 d after pregnancy had abortions. Therefore, the immunization of sows 50 d-80 d after pregnancy was determined.Seven sows during 50 dto 80 d pregnancy were selected for immunization with PRRSV attenuated vaccine. After delivery, 6 piglets were selected for maternal PRRSVantibody detection at 7 d, 14 d, 21 d, 28 d, 35 d, 45 d and 55 d, respectively. The results showed that the piglets maintained high maternal PRRSVantibody levelsduring the postpartum to 21 d. The maternal antibody levels decreased to the critical value(S/P≥0.4 antibody positive) in 35 d. Therefore, the first immunization time was determined in 35 d piglets.