Objectives. The first objective was evaluation of the effectiveness of three porcine circovirus type 2 (PCV2) vaccines available commercially. Criteria used for satisfying this objective included measurement of pig growth from the nursery to finisher phase of growth, determination of antibody responses to vaccination and determination of the prevalence of circovirus in the serum of pigs in the study. The second objective was to evaluate whether vaccination against PCV2 had an impact on porcine reproductive and respiratory syndrome (PRRS) virus circulation and development of clinical disease. Criteria used for satisfying this objective included determination of antibody responses indicating virus exposure and determination of the prevalence of PRRS virus in the serum of pigs in the study.
Experimental plan. The study was completed in a wean-to-finish facility that was supplied by a sow farm that satisfied the case definition for porcine circovirus associated disease (PCVAD) and where PRRS virus had been previously recovered from a pig co-infected with PCV2. Approximately 1023 weaned pigs were assigned to four experimental treatments, which consisted of the three commercial vaccines and a non-vaccinated Control (
Ingelvac Circoflex®, CircumventTMPCV and Suvaxyn® PCV2). Pigs were weighed four times (21, 63, 103 and 144 days of age) during the study to calculate average daily gain and blood was collected from ten pigs in each pen a total of four times (21, 42, 63 and 144 days of age) during the study for analysis of antibody production and to determine the presence of live virus by polymerase chain reaction (PCR).
Results. With the exception of bodyweights obtained at 63 days of age, pig growth data was unremarkable. At 63 days of age, pigs assigned the CircumventTMPCV treatment had lower bodyweights than pigs assigned the Control and Ingelvac Circoflex® treatments. Bodyweights obtained at 21, 103 and 144 days of age were not different. Analysis of the blood for PCV2 indicated that vaccinated pigs had significant increases in the amount of PCV2 antibody in the serum at 42 days of age compared to the non-vaccinated Control pigs. Antibodies were decreased at 63 and 144 days of age for pigs vaccinated with the Ingelvac Circoflex® and Suvaxyn® PCV2 vaccines. Pigs vaccinated with the CircumventTMPCV vaccine, the only two-dose preparation, maintained consistently high antibody levels from 42 days of age to 63 days of age, after which the amount of antibody was reduced at 144 days of age. Viable PCV2 virus was detected among pigs assigned to all experimental treatments. The CircumventTMPCV vaccinated pigs had the greatest percentage of PCV2 virus positive pigs at 21 days of age.  By 42 days of age the non-vaccinated Control group had the greatest percentage of PCV2 virus positive pigs and the percentage of PCV2 virus positive pigs at 63 and 144 days of age was similar for all treatments. Analysis of the blood for PRRS virus yielded highly variable results. The presence of serum antibodies indicated that 35 pigs at 21 days of age, 21 pigs at 42 days of age, 16 pigs at 63 days of age and 234 pigs at 144 days of age had been exposed to PRRS virus. Although antibodies were detected at all sampling time points, attempts to detect viable PRRS virus in the serum of the pigs was unsuccessful.
Discussion/Conclusion. Based on the results of the study, the three commercial vaccines did not have a stimulatory effect on average daily gain because the growth of the vaccinated pigs was similar to the growth of the non-vaccinated Control pigs. The vaccines did stimulate satisfactory antibody production against PCV2 in the vaccinated pigs and although virus was detected in the serum of vaccinated pigs, clinical disease indicative of PCVAD did not develop. The level of PCV2 virus in the environment was perceived to be insufficient to provide a challenge to the non-vaccinated pigs because none showed clinical signs indicative of PCVAD. The level of PRRS virus in the environment was sufficient to stimulate an antibody response that could be measured but live virus could not be detected and clinical signs indicative of active PRRS infection were not observed.