Effect of alum-precipitated or oil-adjuvant Bacteroides nodosus vaccines on the resistance of sheep to experimental foot rot.

The feet of sheep which had been given two doses of oil adjuvant foot rot vaccine were completely resistant to direct challenge with a virulent homologous culture of Bacteroides nodosus four weeks after vaccination, partially resistant after eight weeks but completely susceptible after 12 weeks. Sheep given two doses of alum precipitated vaccine, or a dose of oil emulsion vaccine followed by a dose of alum precipitated vaccine, were resistant four weeks but not eight weeks later. Foot rot in affected, vaccinated sheep was more severe in those which had received the alum precipitated vaccine than in those given the oil emulsion vaccine, but vaccinated sheep were always less severely affected than controls. Where oil emulsion vaccine provided the primary stimulation, agglutinin titres were 18,000 four weeks after revaccination with either vaccine, falling to 4000 after a further four weeks. Significantly poorer titres were observed when two doses of alum precipitated vaccine only were given.