Seroprevalence of Lawsonia intracellularis in large pig production units

In 11 'farrow-to-finish' outdoor or indoor production units, blood samples from late pregnant gilts were tested by indirect immunofluorescence antibody (IFA) serum assay for Lawsonia intracellularis. The offspring of positively tested gilts were tested at 2, 7, 12, 17, 22 and 27 weeks of age for seroprevalence of Lawsonia intracellularis. All offspring of IFA positive gilts were seronegative at 2 and 7 weeks of age. At 12 weeks of age 81.0% of indoor and 51.0% of outdoor pigs were tested positive. While at 17 weeks of age 82.5% of indoor-raised pigs showed seropositivity, in outdoor units the seropositivity declined to 31.3%. At weeks 22 and 27 indoor-raised pigs still showed marked seropositivity (17.7% and 11.5%) but their outdoor-raised counterparts revealed declining values (7.4% and 0%).