What is a major effect of PRRS on pigs?

The major effect of Porcine Reproductive and Respiratory Syndrome (PRRS) on pigs is pneumonia and potential death. PRRS is a viral disease that primarily affects the respiratory and reproductive systems of pigs. It is well known for causing significant respiratory issues in infected animals, which can lead to severe pneumonia. The virus compromises the pig's immune system, making them more susceptible to secondary infections and complications, increasing the risk of morbidity and mortality within herds.

In contrast, other choices describe conditions that do not align with the effects of PRRS. For instance, PRRS is associated with decreased reproductive performance rather than increased reproduction rates. Additionally, it generally leads to poorer weight gain due to the stress and illness caused by the virus, which contradicts the idea of improved weight gain. Lastly, it increases the susceptibility to other diseases rather than decreasing it, as the compromised immune response makes pigs more vulnerable to other pathogens.