Vaccinated piglets exhibited significant levels of serum IgG against Salmonella at the time of challenge. Sera from the control and vaccinated group were pooled into four samples per day. A Sera were analyzed by Western blot against a hot saline antigenic extract of Salmonella ΔXIII strain. In this case, an equal volume of each pool and group was mixed and the resulting samples were used for analysis. C: control, V: vaccinated. B Pooled sera were analyzed by an LPS based IDEXX test. An S/P ratio of ≥ 0.25 is considered positive. Statistical analysis was carried out using a two-way analysis of variance combined with the Bonferroni test. **P < 0.01.