Effect of vaccination against porcine circovirus type 2 (PCV2) on ejaculate characteristics and the shedding of virus in boar semen

Research has demonstrated that porcine circovirus type 2 (PCV2) can be shed into boar semen, raising the possibility that artificial insemination may be an important route by which disease associated with PCV2 is transmitted. The objective of this experiment was to determine the effect of vaccination against PCV2 on ejaculate characteristics and PCV2-specific antibody titers in serum of PCV2-positive boars viremia and viral shedding in semen. Semen and blood samples were collected weekly from week 0 to week 8. After collections at week 0, boars were vaccinated with a commercial vaccine against PCV2 (n = 5) (Suvaxyn PCV2 One dose; Fort Dodge Animal Health, Fort Dodge, IA) or served as controls and received 2 ml 0.9% saline (n = 5). Sperm concentrations and characteristics of sperm motility were assessed using a computer-assisted sperm analysis system (Hamilton Thorne Research, Beverly, MA) and sperm morphology was evaluated after staining using light microscopy. The PCV2 antibody titers were determined in serum using an ELISA (Iowa State Veterinary Diagnostic Laboratory; Ames, IA). The genomic copy number of PCV2 DNA in serum and semen was determined by PCR (Iowa State Veterinary Diagnostic Laboratory; Ames, IA). There were no effects of treatment or treatment by week on semen characteristics (P > 0.05). An effect of treatment by week was detected for serum antibody titers (P < 0.01). Compared with controls, antibody titers in vaccinated boars tended to be greater at week 0 (1.13 ± 0.05 titer/ml vs 1.01 ± 0.05 titer/ml; P = 0.09) and were greater at week 2 (1.15 ± 0.05 titer/ml vs 1.01 ± 0.05 titer/ml; P < 0.05) but lesser at week 7 (1.01 ± 0.05 titer/ml vs 1.23 ± 0.05 titer/ml; P < 0.01) and tended to be lesser at week 8 (1.05 ± 0.05 titer/ml vs 1.17 ± 0.05 titer/ml; P = 0.07). There were no effects of treatment, week, or treatment by week for serum genomic copy number of PCV2 DNA (P > 0.1). An effect of week was detected for semen genomic copy number of PCV2 DNA (P < 0.04). During week 3, PCV2 genomic copy number was at its greatest numerical value, however, semen PCV2 genomic copy number was at its lowest point. This was followed by an increase in semen PCV2 genomic copy number during week 7. This increase could be related to the increase in viral shedding in the serum. In summary, vaccination against PCV2 can lower antibody titers when given post-infection and has no effect on indicators of semen fertility. Vaccination also can decrease the length of reoccurring infection by decreasing the length of viral shedding in serum.