COMPUTER-SIMULATION OF DIFFERENT VACCINATION MANAGEMENTS FOR ERADICATION OF PSEUDORABIES IN PIG BREEDING STOCKS

In this study the influence of vaccination frequency on its efficacy was investigated using a computer model. Previous investigations in sow breeding stocks revealed a number of animals with low or without antibody titers despite the offical recurrent vaccination procedure. The simulation study aimed at proving the assumption that the gaps in immuno protection were caused by the exclusion of certain stages of pregnancy from vaccination, as required on the product label. The non-vaccination of sows in early or late stages of pregnancy or of suckling sows results in gaps of protection which take long periods to diminish. Additionally, the introduction of unvaccinated gilts or boars and re-breeding sows delay this process, resulting in the constant presence of some unprotected single animals in the population. The study shows that a management procedure with five vaccinations per year is able to close the gaps even with the required exclusion of animals in certain reproduction stages. The only alternative would be to vaccinate all individuals of the stock in one cycle regardless to their stage of pregnancy or lactation. This however seems to be unpracticable in the field. The model clearly indicates one of the reasons why the eradication of pseudorabies has not yet succeeded.