RECOVERY OF STAPHYLOCOCCUS-AUREUS FROM CENTRIFUGED QUARTER MILK SAMPLES

The identification of cows that are positive for mastitis caused by St aphylococcus aureus is difficult under field conditions. The frequency of isolation of S. aureus from quarter milk samples was compared with the frequency of recovery of S. aureus from sediment after centrifuga tion of those same samples. Overall, 776 quarter milk samples from 194 cows were studied. Cultures that were positive for S. aureus were obt ained from 82 samples; 153 sediments from quarter milk samples were al so positive for S. aureus. The results of this investigation showed th at cultures of the sediment of quarter milk samples increased the numb er of positive outcomes up to 145.5%, depending on the herd. Using a d ifferent group of samples, including samples taken 1 to 5 d or 7 to 10 d after calving and samples taken after intramammary therapy, a 94% i ncrease in cultures that were positive for S. aureus after centrifugat ion was found compared with cultures of the same quarter milk samples that were not centrifuged. Sedimented cultures may be useful in S. aur eus control programs that require the segregation, selective treatment , or culling of cows that are positive for S. aureus.