| Porcine Reproductive and Respiratory Syndrome(PRRS)is an important infectious disease caused by porcine reproductive and respiratory syndrome virus(PRRSV)infecting pigs.The disease has become the main reason that affects the sustainable development of large-scale pig farming worldwide.PRRSV vaccine immunization is an important means to prevent and control PRRS,which can effectively prevent PRRS outbreaks.Therefore,it is very important to design a scientific and reasonable PRRSV vaccine immunization program.At present,there are two important factors that affect the formulation of PRRSV vaccine immunization programs,the impact of PRRSV maternal antibodies and the immune interference that exists in co-immunization with PRRSV vaccine and other vaccines.The maternal antibodies(MDA)obtained by piglets from colostrum can give piglets a certain degree of immunity,but the high level of PRRSV maternal antibodies in the piglets will interfere with the immune effect of the PRRSV vaccine,and the lower levels of PRRSV maternal antibodies can not provide adequadte protection before the vaccine immunization takes effect.According to the law of the ebb and flow of maternal antibodies combined with the PRRSV vaccine antibody levels of piglets at different ages,the best age for the first immunization in the PRRSV vaccine immunization program for piglets can be determined.Porcine circovirus related diseases(PCVAD)caused by porcine circovirus type 2(PCV2)and swine fever(CSF)caused by swine fever virus(CSFV)are the key diseases to be prevented and controlled in pig breeding and vaccination It is a key means to prevent the occurrence of PCVAD and CSF.PRRSV and PCV2 vaccine or CSFV vaccine co-immunization may cause severe immune interference and immune failure.Therefore,studying the changes of PRRSV maternal antibodies and the interference of PRRSV vaccine immunization on the immune effect of PCV2 and CSFV vaccines can provide theoretical basis and data support for the development of scientific and reasonable immunization procedures for large-scale pig farms.(1)Study on the law of antibody growth and decline of PRRSV live attenuated vaccine and the best age of piglets for first immunization.In this experiment,5 healthy sows were randomly selected from a large-scale breeding farm in Shandong Province and immunized with a classic PRRSV live attenuated vaccine 35 days before delivery.Thirty piglets were randomly selected from the 5 sows delivered,and the anterior vena cava blood of each piglet was collected at the age of 0,4,7,10,16,21,28,and 35 days to separate serum.The level of PRRSV antibody and the positive rate of antibody were determined to explore the growth and decline of PRRSV antibody in piglets.Then selected 175 healthy piglets and randomly divided them into 7 groups.The PRRSV live attenuated vaccine was immunized at 0,4,7,14,21,28,and 35 days of age,and serum was collected at 0,7,14,21,28,and 35 days after immunization to determine the PRRSV antibody level and antibody positive rate.Explore the best age for the first immunization of piglets vaccinated with classic PRRSV vaccine.The results of the study showed that piglets gradually obtained high levels of maternal antibodies after sucking colostrum,reaching a peak on the 4th day and the positive rate was as high as 100%;on the 7th and 10th day,the PRRSV antibodies in the piglets were still near the peak.And the positive rate was 96%;after that,the PRRSV antibody and positive rate gradually decreased,approaching negative on the 28th day,and completely turned negative on the 35th day.In addition,among the piglets of different ages for the first vaccination,the 0-day-old group can produce high levels of PRRSV antibodies on the 7th day after immunization,and the positive rate reaches 75%;after that,the PRRSV antibodies gradually increase,and the positive rate gradually increases.To 100%.In the 4-day-old group,except for the critical value(S/P=3.9)on the 7th day after immunization,PRRSV antibodies were positive at other time points,with a positive rate of70%-83%.The 7-day-old immunization group was similar to the 4-day-old immunization group,except for 7 days after immunization,which was at a lower value(S/P=0.26),and PRRSV antibodies were positive at all other time points.The 14-day,21-day-old,28-day-old and 35-day-old immunized piglets were all negative for PRRSV antibodies before 14 days after immunization,and seroconversion occurred after 14 days or 21 days.(2)The interference effect of classic PRRSV live attenuated vaccine immunization on PCV2 vaccine or CSFV vaccine immunization.This experiment first took 100 piglets as the research object and randomly divided them into 4 groups A,B,C,and D.Among them,piglets in group A were immunized with classic PRRSV live attenuated vaccine 7 days later and immunized with PCV2 vaccine;piglets in group B were injected with classic PRRSV live attenuated vaccine and PCV2 vaccine at the same time;piglets in group C were only immunized with PCV2 vaccine;piglets in group D were immunized only with classic PRRSV reduced Live virus vaccine.In addition,another100 piglets were screened and randomly divided into 4 groups E,F,G,and H.Piglets in group E were immunized with CSFV vaccine 12 days after being immunized with classic PRRSV live attenuated vaccine;piglets in group F were injected with classic PRRSV live attenuated vaccine and CSFV vaccine at the same time;piglets in group G were immunized only with CSFV vaccine;piglets in group H were immunized only with classic PRRSV reduced Live virus vaccine.After 4 weeks of immunization,the level of related antibodies in the piglet's serum was determined.At the same time,weigh the piglets of each group before and after immunization,and calculate the average daily gain of piglets with different immunization programs.The results of the study showed that in the A-D group,the piglets of group A and group B produced higher levels of PRRSV and PCV2 antibodies after 4 weeks of immunization,and the antibody level of group A was slightly higher than that of group B.Piglets in group C only produced antibodies to PCV2,and piglets in group D produced higher levels of antibodies to PRRSV.In the E-H 4 group,the piglets of the E group and the F group produced higher levels of PRRSV and CSFV antibodies.Piglets of G group only produced high levels of CSFV antibodies,and piglets of H group only produced high levels of PRRSV antibodies.The average daily gain of piglets in group B was the highest among the 4 groups of A,B,C and D;while the average daily gain of piglets in group E in the 4groups of E,F,G and H was significantly higher than that of the other 3 groups.Classical PRRSV live attenuated vaccine and PCV2 vaccine or CSFV vaccine at the same time split immunization,immunization with classic PRRSV live attenuated vaccine for a period of time and then immunization with PCV2 or CSFV vaccine can induce piglets to produce high levels of antibodies,none of which shows obvious immunity interference.To sum up,(1)The law of the PRRSV live attenuated vaccine antibody growth and decline and the best piglet's first vaccination age test results show that the piglets are given the first classic PRRSV live attenuated vaccine on the day of delivery(before colostrum sucking)or 4 to 7 days after delivery(VR2332)Immunization can make piglets quickly produce high levels of positive antibodies,and has a longer duration of immunity and PRRSV antibody positive rate,which is a more reasonable immunization program.(2)The interference effect of PRRSV live attenuated vaccine immunization on PCV2 vaccine or CSFV vaccine test results show that the immunization of classic PRRSV live attenuated vaccine and PCV2 vaccine at the same time at 28 days of age in piglets,the immunization program of immunization with CSFV vaccine after 12 days can not only Inducing piglets to produce high levels of antibodies can also make piglets have a higher average daily gain.The development of this research will provide important data support and experience reference for the development of scientific and reasonable classical PRRSV live attenuated vaccine procedures for large-scale pig farms. |
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