Vaccination against experimental staphylococcal mastitis in ewes

Experiments were carried out in ewes using a new vaccine developed for the prevention of mastitis caused by Staphylococcus aureus. The vaccine comprised three major components: (i) killed S aureus cells which had been cultured to induce synthesis of pseudocapsule; (ii) toxoided staphylococcal beta haemolysin and (iii) the adjuvant dextran sulphate. Ewes systemically vaccinated twice during pregnancy developed significantly elevated circulating levels of IgG1 and IgG2 anti-pseudocapsule antibody, as well as increased serum titres of anti-beta haemolysin. Five different strains of S aureus were used to challenge both vaccinated and control ewes by the intramammary route during the ensuing lactation. The incidence of acute gangrenous mastitis and nonacute, clinical mastitis was significantly lower in vaccinated than in control groups after challenge with each strain. Vaccinated ewes produced significantly more milk than control ewes after challenge with four of the five strains of S aureus.