Lawsonia intracellularis: humoral immune response and fecal shedding in weanling foals following intra-rectal administration of frozen-thawed or lyophilized avirulent live vaccine.

The humoral immune response and fecal shedding of Lawsonia intracellularis was investigated in 20 weanling foals following intra-rectal administration of frozen-thawed or lyophilized avirulent live L. intracellularis vaccine. Foals received either 30 mL frozen-thawed or lyophilized vaccine intra-rectally, given twice, 4 weeks apart. Serum samples from each foal were collected every 4 weeks for 16 weeks following the first vaccination and tested for anti-L. intracellularis specific IgG by immunoperoxidase monolayer assay. Rectal swabs were collected every other day following the first vaccination for 4 weeks for detection of L. intracellularis by real-time PCR. Both vaccine formulations administered intra-rectally in weanling foals were safe and led to similar onset and duration of fecal shedding and measurable serum IgG response against L. intracellularis.