Evaluation of Protein A and a Commercial Bacterin as Vaccines Against Staphylococcus aureus Mastitis by Experimental Challenge

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Abstract
Protein A and a commercial staphylococcal bacterin were evaluated by experimental challenge with S. aureus (ATCC 29740). Thirty cows in 1st lactation were in 3 treatment groups, protein A, bacterin and nonvaccinated controls. Studies were through 3 lactations and included bacteriological and cytological analyses of quarter milk samples. Rate of intramammary infection with S. aureus was similar for vaccinated and unvaccinated cows. Rates of spontaneous cure within each lactation were significantly higher for vaccinated cows. For all 3 lactations, spontaneous cure rates were 83, 73 and 47% for protein A, bacterin and control cows. Somatic cell counts were significantly lower for vaccinated cows for quarters infected with S. aureus, but no differences were demonstrated for milk production by lactation. Incidence of clinical mastitis was higher in unvaccinated cows, but too few developed for a valid comparison.