The evaluation of protection efficacy of the various trial vaccines and reference vaccines for swine coiibacillosis control was carried out on mice by intraperitoneal immunization test. The results indicated that the vaccines prepared with different serotypic strains had cross immunization with each other in spite of the differences of their somatic andor surface antigen structures. The potency was up to 90-100%. 11 the bacterial suspension used for challenge was 10 times condensed, even in homologous strains, the survival rates were down to S0°o or less. For bacterial cell free or surface antigen free vaccine, the protection efficacy in mice was usually lower.
Therefore, in the evaluation on protection efficacy of swine Escherichia coli vaccine, it is recognized to be with portection value either the survival rate was US0% in experimental group and mortality wasU80°o in control group or the protective index (LDSO) was equal to or more than l0’O.5.