Effect of vaccination against sub-clinical Porcine Circovirus type 2 infection in a high-health finishing pig herd: A randomised clinical field trial.

During the last decade, the clinical manifestation of Porcine Circovirus type 2 (PCV2) infections has mostly changed from postweaning multisystemic wasting syndrome and high mortality to sub-clinical infections manifested only through impaired production parameters. However, co-infection with other respiratory pathogens often results in a larger effect on production, sometimes with clinical signs. Little is known about the impact of a moderate level PCV2 infection without co-infections, particularly in terms of feed conversion ratio and antimicrobial consumption. The purpose of the study was to evaluate the effect of vaccination against PCV2 in a sub-clinically infected, high-health finishing herd in terms of viral load in serum, feed conversion ratio and antimicrobial treatments. The study was conducted as a randomised clinical field trial with a parallel group design. Vaccination against PCV2 significantly (p<0.001) reduced the prevalence of PCV2-positive serum pools, from 91% in the control group to 6% in the vaccinated group, as well as the viral load for positive pools from 5.79 to 3.99 log(10) copies per ml serum. Despite this, feed conversion ratio for the two groups were not significantly different with an average of 2.75 and 2.76 feeding units/kg gain for vaccinated and control pigs, respectively (p=0.598). The proportion of pigs treated by injection with an antimicrobial was lower in the vaccinated group (4.4%) compared to the non-vaccinated group (5.6%), but the difference was not significant (p=0.125). In conclusion, in this herd without respiratory co-infections and with moderate viral loads of PCV2, vaccination significantly reduced the prevalence and viral load of PCV2-positive pigs, but had no significant impact on feed conversion ratio or antimicrobial consumption.