The secret to consistently producing PCV2-negative pigs is PCV2-negative sows. Vaccination can help maintaining protective immunity in the sow herd that will not only positively affect the sows but also their piglets.

Even if elimination of PCV2 is not possible, farms can achieve an extremely low level of PCV2 prevalence. Without actual elimination, maintaining such status requires on-going control measures. Absolute absence of PCV2 in weaned piglets cannot be guaranteed, but consistent production of (almost) PCV2-negative batches seems to be possible. If piglets are then actively immunized to protect from future challenge, there should be no opportunity for PCV2 to have a negative impact on production, allowing producers to achieve a higher level of control.

Negative sows are the key

As noted, the main requirement to produce PCV2-negative piglets from a sow farm is negative sows. However, that is not an easy task. Maintaining a low-prevalence sow herd requires limiting virus introduction then limiting virus spread if it is introduced to the herd. While there may be other routes of infection, the highest risk for new virus to enter the herd is likely to be replacement gilts. The major influence on spread will be immunity, which in a largely negative herd, will reflect vaccination.

In principle, replacement gilts should be free of PCV2 and have high immunity. Thus, they represent neither a source of virus nor a pool of vulnerable animals that could multiply virus already present. Guaranteeing PCV2-negative gilts may be difficult, but the chances should be high if the gilts come from a low-prevalence source and are vaccinated before they become infected.

Maintaining protective immunity in the sow herd is potentially more complicated. Sow vaccination will not only affect the sow but also the piglets, perhaps requiring changes to the vaccination protocol for piglets.

Benefits of sow vaccination

Protection of sows from PCV2-related reproductive disease (PCV2-RD). PCV2 infection in sows has been linked to abortion and stillbirths, with presence of lesions and PCV2 in fetal tissues. A high level of vaccine-induced immunity is expected to prevent or at least reduce these types of reproductive losses. However, no vaccine has a licensed claim relating to PCV2 reproductive disease.

Protection of piglets through provision of maternal immunity. Not surprisingly, sow vaccination will increase maternally derived antibodies (MDA), which should extend the duration of passive protection in piglets and reduce the variability of the MDA protection provided.

Protection of piglets through reduction in exposure to virus from the sow herd. Piglets may become infected before they ingest colostrum, and these infections are not typically cleared by subsequent colostrum intake or active immunization. Although much less common than it was, a high level of vertical transmission may still be found in specific herds, and even a low level may be significant as a source of virus in batches of weaned pigs.