Immune Antibody Monitoring And Immunization Program Optimization Of FMD And PPR Vaccine In Large-scale Sheep Farm

Foot-and-mouth disease(FMD)and Peste des petits ruminants(PPR)are potent animal infectious diseases that are forced to immunize in China.The outbreak of FMD and/or PPR will seriously harm biosafety and animal husbandry economy.As a large country in the sheep breeding industry,China has always taken FMD and PPR prevention and control as the focus of epidemic prevention work.The sheep in a large-scale sheep farm in the Guanzhong area of Shaanxi Province are immunized twice with FMD vaccine on spring and autumn(March,September)every year,and immunized with PPR vaccine on spring(April).In this study,the antibody level after vaccine immunization was monitored by enzyme-linked immunosorbent assay(ELISA).By comprehensive analyzing the levels of FMD and PPR specific antibody according to the original immunization protocol,the feasible immune program was optimized and developed.Which ensure the immune effect of the flock immunized with foot and mouth disease and small ruminant vaccine.The obtained results are as follows:1.In August,2018(one month before the autumn),blood samples of foot-and-mouth O-A type bivalent inactivated vaccine-immunized sheep were collected.The average positive rate of suffolk sheep FMDV-O type and FMDV-A type specific antibodies were68.33% and 66.67%,respectively,that lower than 70% positive rate of immunization requirements;The average positive rates of FMDV-O type and FMDV-A type specific antibodies in Doper sheep were 80% and 83.33%,respectively,reaching the 70% positive rate of immunization requirements.In September 2018,Suffolk flock and Doper sheep were immunized with foot-and-mouth O-A type bivalent inactivated vaccine,and serum samples were collected at 6 months after immunization(before the new immunization cycle in March of the following year)for antibodies levels detection.The average positive rates of FMDV-O type and FMDV-A type specific antibodies in Suffolk flocks were 57.14% and 55.71%,respectively.The average positive rates of FMDV-O type and FMDV-A type specific antibodies in Doper sheep were 62.86% and 64.28%,respectively,that lower than 70%positive rate for immunization requirements.In order to reduce the effect of maternal antibodies on vaccine immunization,the lambs were immunized with foot-and-mouth O-A type bivalent inactivated vaccine at 60-day-old in the original immunization program of the sheep farm.Then,we monitored the levels of maternal antibodies in lambs by ELISA assay.The results showed that the positive rates ofmaternal antibodies specific of FMDV-O type and FMDV-A type were 60% and 55%,respectively,at 21 days of age,which was lower than the 70% positive rate.We detected the antibody levels of lambs immunized with foot-and-mouth O-A type bivalent inactivated vaccine at 21-day-old.The results showed that the positive rate of FMDV-O antibody reached 100% at the 28 day after immunization,and the positive rate of FMDV-A antibody reached 100% at the 35 day after immunization.The positive rates of FMDV-O and FMDV-A antibodies were 80% and 70%,respectively,at 150 days after immunization.2.In August,2018,the serum samples of the flocks immunized with the small ruminant plague vaccine(Clone 9 strain)were collected after 4 months.The ELISA test showed that the average antibody positive rate of the adult sheep and the bred sheep of Suffolk and Doper sheep reached 100%.The average antibody positive rate of the young sheep population were50% and 40%,respectively.In view of the low positive rate of PPRV specific antibodies,we performed a second booster immunization of the PPR vaccine on the young sheep population and monitored the antibody levels.The results showed that the PPRV antibody levels were significantly increased in the experimental group(secondary immunization)at 14 day and 21 day after immunization compared with the control group(no secondary immunization).The antibody positive rate reached 100% at 21 days after immunization.In order to reduce the effect of maternal antibody on vaccine immunization,the lamb were first immunized with PPRV vaccine(Clone 9 strain)at 90-day-oldin the original immunization program of the sheep farm.Then,we monitored the kinetics of maternal antibodies in lambs by ELISA assay.The results showed that the positive rates of maternal antibodies of PPRV was 55%,respectively,at 90 days of age,which was lower than the 70%positive rate.We detected the antibody levels of lambs immunized with PPRV vaccine(Clone 9 strain)at 90-day-old.The results showed that the positive rate of PPRV antibody reached 100% at 28 days after immunization.The positive rates of PPRV antibodies was80%,respectively,at 150 days after immunization.In March 2019(before the new immunization cycle in April of the following year),we collected PPR vaccine-immunized sheep blood samples.The ELISA assay showed that the positive rate of PPRV antibody was56.67%.In summary,by monitoring and analyzing the antibody levels of the sheep immunized with the foot-and-mouth and the small ruminant vaccine according to the original immunization program of the sheep farm,it is found that the original immunization program is insufficient.It is recommended that the time(September)for foot-and-mouth O-A type bivalent inactivated vaccine immunization for Suffolk sheep should be advanced by onemonth.The lamb first immunization for foot-and-mouth OA type bivalent inactivated vaccine is advanced to 21 days of age.In addition,the youth of Suffolk and Dubo sheep should immunized again after 4 months of first immunization with the PPR vaccine.