Derivation of porcine circovirus type 2-negative pigs from positive breeding herds

Objective: To summarize procedures utilized to derive piglets negative both for porcine circovirus type 2 (PCV2) and for antibody to PCV2, from PCV2-positive breeding herds. Methods: Sow herds were screened for antibodies to PCV2 by ELISA, with sample-to-positive (S:P) ratios >= 0.2 considered positive. Piglets were obtained by segregated early weaning (SEW) at 10 to 12 days of age. Maternal anti-PCV2 antibody was determined by testing weekly blood samples by ELISA and indirect immunofluorescence assay. Absence of PCV2 was determined by polymerase chain reaction (PCR) on weekly serum samples and by PCR and immunohistochemistry assays on lymphoid tissues collected at necropsy (8 to 15 weeks of age). Results: Piglets negative for PCV2 by PCR and for anti-PCV2 antibody were derived from PCV2-positive breeding herds. Mean PCV2-antibody half-life in weanlings was estimated to be 19.0 days (95% confidence intervals, 17.6 and 20.3 days). Passively acquired PCV2-antibody present at 10 to 12 days of age declined to S:P ratios < 0.2 by 4.9 +/- 1.2 weeks of age in piglets with S:P ratios >= 0.2 and < 0.6; by 8.1 +/- 1.9 weeks in piglets with S:P ratios >= 0.6 and <= 1.0; and by 11.1 +/- 2.5 weeks in piglets with S:P ratios >= 1.0. Pigs kept in isolation remained PCV2-negative by PCR and ELISA through 8 to 15 weeks of age. Implications: SEW may be an effective technique to derive PCV2-negative piglets from positive breeding herds.