A University of Nebraska study has confirmed that weight gains and levels of viremia (infection in the bloodstream) are not linked, but together the two variables provide a good sign of response to the porcine reproductive and respiratory syndrome (PRRS) virus.

The research bears out the commonly held notion that there is variation in pigs’ immune response to the PRRS virus.

The hypothesis pursued in this project is that some of the variation in immune response is due to the pig’s genetic makeup, and that selection for genes that inhibit viral replication may reduce the incidence and severity of the disease.

In this study, 220, 34-day-old pigs free of PRRS virus were transported from their farm of origin to the wean-to-finish barn at the Haskell Agricultural Laboratory at Concord, NE. The pigs were randomly allotted to one of 16 pens and housed 12-14 pigs/pen.

Following a 19-day adjustment period, pigs were injected with the PRRS virus, blood was drawn and weights taken at several time periods.
Correlation among weights and levels of viremia were relatively low. Weight gain from 0 to 4, 4 to 7, 7 to 14 and 14 to 35 days post-inoculation were negatively correlated with viremia at 4, 7 and 14 days post-inoculation.

The data in this study is consistent with previous studies in that weight gains and viremia are not highly correlated, but together they represent a good index of response to PRRS virus.

Moreover, the distribution of pigs with various levels of viremia at 4, 7 and 14 days post-inoculation suggest that some pigs have low replication rates, while others have very high replication rates. This finding suggests underlying variation in the pig’s immune response to virus.

Funding for this research project was provided by the National Pork Board.

Researcher: Donald Levis, University of Nebraska. For more information, contact Levis by phone (402) 370-4000 or e-mail dlevis@unlnotes.unl.edu.