FIG. 1.

Kinetics of PCV2 antibody in response to infection and PCV2 maternal antibody decay for each group of piglets throughout the experiment. Piglets in groups A, B, and C were exposed to PCV2 at day 0 (day postinoculation). Piglets in group D were not exposed to PCV2 at day 0 but were challenged with a homologous PCV2 at day 42, along with all piglets in the other groups. The criteria used to assign piglets to groups on the basis of maternal antibody levels prior to inoculation with PCV2 were as follows: group A, n = 6, negative maternal antibody (S/P ratio, <0.2); group B, n = 5, low level of maternal antibodies (S/P ratio, >0.2 to <0.5); groups C (n = 8) and D (n = 5), high level of maternal antibodies (S/P ratio, >0.5). Pig identification (ID) numbers are given. The broken lines show an S/P ratio of 0.2.