How is it done?

Stochastic models simulated PRRS outbreaks on a hypothetical small, medium, or large farrow-to-weaning swine farm in the Midwestern United States. Different control strategies were compared in the models: from none to 4 several combinations of immunization, herd closure, and gilt acclimatization. In addition, by combining 3 virulence status of PRRSv and 3 herd sizes, nine different models were simulated.

The goal in each simulation was to have negative PCR results on 3-week old piglets (PRRS stability).

What are the results?

Increasing PRRS virus virulence and herd size were negatively associated with the probability of achieving a stabilized status. Virulence level appeared to have a greater influence on the probability of the farm achieving a stabilized status than did herd size.

For the baseline scenario (no PRRS control strategies implemented), a stabilized status was achieved only in the model for small herd size and low PRRS virus virulence.

Repeated mass immunization with herd closure or gilt acclimatization was a better alternative than was single mass immunization for disease control within a farm.

What implications does this paper have?

For a farrow-to-weaning swine farm, with the goal to reach breeding herd stabilization the recommendation is to implement repeated mass vaccination with a PRRS MLV every 15 also, herd closure appeared to be more beneficial than only gilt acclimatization.