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Translator's words: Pig breeding and respiratory syndrome (PRRS) has always been one of the difficulties that plague the pig farming industry. Due to the complexity of PRRS, there is no agreement on the control of PRRS immune procedures in China. However, for PRRS-positive pig farms, immune monitoring is very important, especially for newly introduced reserve pigs. In this study, the authors conducted pathogens and antibodies monitoring on reserve pigs introduced by 69 PRRS-positive pig farms, and found that some reserve sows had negative antibody test results after receiving live vaccines. This result suggests that monitoring of PRRSV antibody levels in reserve pig herds should be strengthened in production to avoid later production losses caused by immunization failure.
This study analyzed PRRSV live vaccine immunization and isolation facilities in 69 PRRS-positive sow farms to monitor the PRRSV infection status of introduced reserve sows at the first artificial insemination.
Introduction
Pig Reproductive and Respiratory Syndrome Virus (PRRSV) is an important disease pathogen that threatens the global pig farming industry, including Denmark. After the pig herd is infected with PRRSV or vaccinated with live PRRSV vaccine, blood sample testing will cause viremia for a period of time, so the virus is easily transmitted to PRRSV-negative pigs. In Denmark, for PRRS-positive sow farms, it is recommended to perform 12 weeks of isolation and domestication after introduction of reserve sows.
The purpose of this study was to compare the immunization and isolation facilities of PRRSV live vaccines performed in 69 PRRS-positive sow farms to monitor the PRRSV infection status of introduced reserve sows at the first artificial insemination. In addition, the antibody level will be evaluated in this study.
Materials and methods
This study subject was 69 PRRS-positive sow farms in Denmark. During the first artificial insemination of each pig farm, five blood samples were taken for RT-qPCR, ELISA and IPMA laboratory tests. These pig farms were also questionnaires on the introduction strategies and immunization procedures of reserve sows, and data were collected for later analysis.
backup sow status analysis data are whether to isolate, quarantine time and reserve sow introduction plan (outbound purchase or cultivation in this farm). The antibody level analysis was ELISA and IPMA detection (analysed based on the time of vaccine immunization and the age of immunized pigs).
Figure 1 Introduction strategy for reserve sows in 69 pig farms
Figure 2 Isolation status of reserve sows in 69 pig farms
Table 1. Isolation facilities status (46 isolated pig farms)
Note: *, there is a pig farm data error, exclude
Results
69 pig farms, 40 (58%) were external introduction, 22 (32%) were cultivated in this farm, and the remaining 7 had two strategies. 70% of the reserve sows introduced externally were isolated, and only 50% of the reserve pig breeds cultivated in this farm took isolation measures. In addition, only 10 pig farms have standards-compliant isolation facilities, with an isolation period of 8-16 weeks.
laboratory tests show that 63 pig farms are PRRS stable pig herds, and 6 are unstable. Stable pig herds mean that RT-qPCR test is negative (viremia negative) and ELISA test is positive (antibody positive). All pig farms had negative RT-qPCR tests, but 6 pig farms had negative PRRSV antibody tests, so these 6 pig farms were defined as PRRS unstable pig farms.
Statistical results show that factors such as isolation, isolation time, and reserve sow introduction strategies do not differ significantly between stable pig farms and unstable pig farms, but the use of isolation facilities will make the pig herd more stable. The difference in antibody levels in the pig herd at the first artificial insemination was not significant.
Discussion
Theoretically, the reserve pig herd without isolation measures should be positive for viremia during laboratory testing. However, the duration of viremia after live vaccination is about 4 weeks, while the average sample collection time is about 18 weeks (at the first artificial insemination). Therefore, all the test results of the samples were negative for PRRS virus. The negative antibody test in 6 pig farms indicates that the reserve sows had not received immunization or the antibody level had dropped at the time of the first artificial insemination. These six pig farms were all immune to live vaccines before breeding, and the theoretical level of antibody should last for about 18 weeks, so this result shows that the antibody level of these six pig farms is declining. Negative reserve sows are susceptible to viral infection during pregnancy and can easily lead to the spread of the virus in the delivery room.
Conclusion
The results of this study show that among the 69 PRREV-positive pig farms in Denmark, although the isolation conditions and measures are largely different, they are all negative in the laboratory test results. However, the continuous introduction of negative reserve sows and inadequate monitoring of immune effects may lead to the production of PRRSV-susceptible pigs and lead to clinical PRRS outbreaks. Therefore, needs to strictly monitor the immune effect of the PRRSV vaccine in the reserve sows in the pig farm.
◤ The reserve sows in this field also need to be isolated ◢
Original author: Bonnie Edahl Hoelstad, Denmark
Translator: Xie Xiaoyu
Article source: https://www.pig333.com/
Xie Xiaoyu
Intermediate veterinary
Intermediate veterinary
committed to the clinical application of pig farm vaccines, antibody detection and molecular epidemiological investigation, and have a high theoretical background and rich practical experience in epidemic monitoring.
