INFLUENCE OF PARITY AND STAGE OF LACTATION ON THE SOMATIC-CELL COUNT IN BACTERIOLOGICALLY NEGATIVE DAIRY-COWS

This study examines the influence of parity, stage of lactation, and s ingle isolations (i.e., the isolation of a microorganism that could no t be reisolated in the same quarter in the next sampling) of staphyloc occi other than Staphylococcus aureus (coagulase-negative staphylococc i), Corynebacterium bovis, or esculin-positive cocci other than Strept ococcus uberis (referred to as esculin-positive cocci throughout) on t he monthly log(e)-transformed somatic cell count (SCC) for 180 first, second, and third parity cows that were observed over a whole lactatio n. Repeated measures ANOVA was used to analyze the data. No significan t effect was found for the infection variable. However, the results in dicated that even single isolations of coagulase-negative staphylocci, C. bovis, or esculin-positive cocci resulted in a numerical or statis tically significant increase in SCC. Least squares mean SCC (log(e)-tr ansformed) for bacteriologically negative cows and cows with single is olations of coagulase-negative staphylococci, C. bovis, or esculin-pos itive cocci were 3.90, 3.97, 4.08, and 4.17, respectively. Significant effects of parity, stage of lactation, and the interaction of parity and stage of lactation could not be found when only bacteriologically negative cows were considered. Least squares mean SCC for first, secon d, and third parity cows were 3.80, 3.93, and 3.97, respectively. Howe ver, the effects of parity, stage of lactation, and the interaction of parity and stage of lactation were significant when all 180 cows were included. Therefore, these effects must be due to factors that were p resent in the infected groups.