Serological prevalence of PCV2 in the different age categories of pigs. The pig populations were categorized into 4 groups, including nursery pig (2-10 weeks), fattening pig (10-26 weeks), gilt (>26 weeks, non-serviced) and sow (>26 weeks, serviced). The immune response levels are presented in three categoris, negative (S/P ratio of 0.49 or less or the titer of ≤1,070), low positive (S/P ratio of 0.5-2.3 or the titer of 1,071-5,766) and high positive (S/P ratio of 2.31 or greater or the titer of ≥5,767).