A team of scientists working together with the Agricultural Research Service (USDA) in the US have discovered a vital clue to counteract porcine reproductive and respiratory syndrome virus (PRRSV).
The virus costs US swine producers around US$560m yearly. It causes pneumonia and reproductive losses in pigs and infected sows to give birth to weak piglets. Pigs require weeks or months to recover from the virus, which is not very responsive to medications or vaccines.
Scientists evaluated two lines of swine for their genetic resistance to PRRSV. They chose the Hampshire by Duroc cross (H.D.) for its high growth rates and the Nebraska Index Line (I) for its improved reproductive traits.
After exposure to PRRSV, all pigs became infected. However, the I line pigs generally recovered more quickly.
Samples of blood, lung and bronchial lymph node tissue indicated that the virus cleared up more quickly in I and H.D. pigs, who were resistant to PRRSV.
A study of the tissue expression of 11 genes and one ‘housekeeping’ gene in the immune response to PRRSV was carried out. The results showed that both swine lines had significant activity in 11 of the 12 genes, but the type differed greatly between the two.
The above findings are highly significant as they support existing research that maintains that animal breeds with high growth rates devote less energy to immune and disease traits.