To control an unstable PRRS situation, a farm did more than 4 times a PRRS mass vaccination with 2 different commercial NA type MLV (one commercial vaccine in one week, and the second vaccine the following week, by turns). After 8 weeks from first mass vaccination, they found high fever and stillborn (confirmed PRRSv positive by PCR). This kind of excessive PRRS vaccination to sows in less than 8 weeks before farrowing, could it be the main cause of stillborn and high fever?
Symptoms of fever and stillborn with PCR positive to PRRSv are a strong evidence of probable PRRSV viremia, in late gestation.
If there were 4 PRRS vaccinations with 2 different live PRRSv vaccines, in 4 consecutive weeks, this is a massive immune challenge to the pregnant sow and for the unborn piglets.
The viremia after one PRRS vaccination with a live vaccine in late gestation is not enough to cause abortions or significant stillborn.
But such a huge viral load after 4 weeks of repeated PRRS vaccinations, in my understanding, can cause these symptoms.
I do not see the benefits of such a PRRS vaccination scheme because there is not enough time to allow the immune system to process so much antigen in a proper way.nd very difficult to control in endemic regions.
For more information about this subject, visit chapter 4 “Immunisation of gilts and sows” of this site.
Universidade Lusófona de Humanidades e Tecnologias – Portugal