One hundred and fifty-nine cases of clinical Staphylococcus aureus mastitis were analyzed to detect factors associated with bacteriological cure after therapy. On 100 Dutch dairy farms, data were collected from four clinical trials with five intramammary treatment regimes designed to treat beta-lactamase-positive pathogens. Infected quarters were treated three times, with a 12-h interval between treatments. Treatment was extended for 2 d if results of the trial treatment were, according to the owner, not satisfactory. The overall bacteriological cure rate was 52%. The bacteriological cure rate of clinical beta-lactamase-negative S. aureus mastitis was significantly higher than that of clinical beta-lactamase-positive S. aureus mastitis. Bacteriological cure was also significantly higher if somatic cell count of the cow was low at the milk recording prior to the onset of the clinical mastitis. The bacteriological cure rate of clinical beta-lactamase-negative S. aureus mastitis was also significantly higher after an extended treatment compared with no extended treatment. The seriousness of the various clinical symptoms and the bacteriological cure rate of clinical S. aureus mastitis were not associated.

The objective of this study was to determine the factors that were associated with the cure of subclinical mastitis caused by Staphylococcus aureus treated during lactation. One hundred forty-three quarters that were infected with S. aureus were available from a number of treatment trials. Analysis of these data showed that the most important factors associated with cure were age of the cow, somatic cell count at the time of treatment, presence of the infection in the front quarters, and stage of lactation. Other factors, such as number of infected quarters per cow and sensitivity or resistance of the strain to penicillin, were not significant. Because of the relatively low probability of cure, it is important to know risk factors for cure and, hence, to choose cows for treatment with great care. Using these data, a prediction equation was developed to determine the cure rate of subclinical mastitis caused by S. aureus when treated during lactation.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Page 1 making it the most frequently isolated group of pathogens. Fourteen species of CNS were 7 identified; the most frequently isolated species was Staphylococcus chromogenes (30.3%) 8 followed by Staphylococcus epidermidis (12.9%) and Staphylococcus capitis (11.0%). 9Prevalence of CNS IMI was higher in heifers compared to older cows. Geometric mean 10 quarter SCC of CNS-positive quarters was 109,000 cells/ml, which was approximately twice 11 as high as culture-negative quarters. Quarters infected with S. chromogenes, S. capitis and 12Staphylococcus xylosus had a higher SCC (P<0.05) than culture-negative quarters, while 13 quarters that were culture-positive for S. epidermidis and Staphylococcus hyicus tended to 14 have a higher SCC than culture-negative quarters. An increased prevalence of CNS IMI was 15 associated with the herd level variables source of drinking water not being tap water, housing 16 of dry cows in one group instead of multiple groups, measurement of cow SCC every month, 17 udder health monitoring by the veterinarian, pasturing during outdoor season, percentage of 18 stalls contaminated with milk, and BMSCC >250,000 cells/ml. Although a causal relation 19 between these factors and prevalence of CNS is not proven and for some factors not even 20 likely, knowledge of the associations found may by helpful when approaching CNS problems 21 on dairy farms. 22 23

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