Effects of porcine reproductive and respiratory syndrome virus infection on the performance of pregnant gilts and growing pigs.

This study examined the effects of porcine reproductive and respiratory syndrome virus (PRRSV) infection on (1) pregnant and (2) growing Landrace and crossbred (Large White x Pietrain) pigs. First, recently pregnant gilts were spilt into a control and a challenged group, which was inoculated with the PRRSV, and phenotypic effects were recorded. In the Landrace breed, infected gilts had a significantly reduced number of fetuses (8.9 versus 11.8), but there were insufficient data to make the same comparison in crossbred gilts. The Landrace had a smaller suppression of weight gain during pregnancy than the crossbred line [56% (0.66 to 0.29 kg/day) versus85%(0.45 to 0.07 kg/day) reduction], suggesting greater tolerance of the PRRSV infection. Second, impacts on growing pigs were examined with the same deliberate challenge methodology. Some pigs appeared not to become infected from the initial inoculation, but were possibly subsequently infected by cohorts. However, there were indications of Landrace line resistance in terms of an increased time to seroconvert, with weight gain patterns also suggesting Landrace tolerance. In summary, this study demonstrated that breeds differ consistently in phenotypic impacts of PRRSV infection.