Beschreibung:
<jats:p>The objective of the study was to determine etiologic agent(s) of intramammary infections (IMI) in high somatic cell count (SCC) dairies in Tennessee. This was a prospective study utilizing 2,444 dairy cows from 20 high SCC dairy herds. Composite milk samples were aseptically collected from lactating cows in 20 dairy herds with a rolling herd average SCC >400,000 cells/mL. Milk samples were cultured and mastitis pathogens identified following procedures recommended by the National Mastitis Council. The average herd percentage (average of the 20 herd averages) of culture-negative cows was 49%. The average herd percentages of positive-culture cows were 28% for coagulase-negative staphylococci (CNS), 15% for Staphylococcus aureus, 10% for environmental streptococci (ES), and ?2% for gram-negative organisms. Among cows with individual SCC >1 million cells/mL, 30% of cultures yielded Staph. aureus, 23% CNS, 26% no growth, 26% ES, and 5% gram-negative organisms. Among cows with individual SCC >400,000 cells/mL, cultures yielded 26% CNS, 30% no growth, 28% Staph. aureus, 21% ES, and 4% gram-negative organisms. Staph. aureus was the most common major pathogen, or equally common major pathogen, in 75% of high SCC herds. Environmental streptococci were the most common major pathogen, or equally common major pathogen, in 45% of high SCC herds. Staph. aureus is the major pathogen, followed by ES, among Tennessee dairy herds with high SCC. Coagulase-negative staphylococci are common, but their significance needs to be determined. Gram-negative organisms do not appear to be significant pathogens of Tennessee dairy herds with persistently high SCC.</jats:p>