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* Department of Production Animal Clinical Sciences, Norwegian School of Veterinary Science, Oslo, Norway
Department of Norwegian Cattle Health Services, TINE Norwegian Dairies Association, Ås, Norway
Departments of Biostatistics and Statistics, University of Kentucky, Lexington, 40536
1 Corresponding author: Olav.Reksen{at}veths.no
In quarter milk samples from 2,492 randomly sampled cows that were selected without regard to their current or previous udder health status, the relationships between the following outcome variables were studied: treatment of clinical mastitis; the joint event of either treatment or culling for mastitis; culling for all reasons; culling specifically for mastitis; and the covariates of positive milk culture for Staphylococcus aureus, Streptococcus spp., and coagulase-negative Staphylococcus spp., or other pathogens, or of negative culture for mastitis pathogens. Microbiological diagnoses were assigned at the cow level, and altogether 3,075 diagnoses were related to the outcome variables. The relation between the absence of pathogens and rich (>1,500 cfu/mL of milk) or sparse (
1,500 cfu/mL of milk) growth of Staph. aureus were also assessed separately for each outcome variable. The hazard of treatment of clinical mastitis was greater for cows diagnosed with Staph. aureus compared with cows with no pathogens in all analyses. Cows with sparse growth of Staph. aureus upon microbiological analysis were more likely to be treated for clinical mastitis, and cows with rich growth of the bacteria experienced a higher overall risk of culling when the models adjusted for cow composite milk somatic cell count. No difference between rich and sparse growth of Staph. aureus was found when mastitis was defined as the joint event of either culling for mastitis or treatment of clinical mastitis, and when the relationship with culling specifically for mastitis was assessed. The combined outcome of treatment and culling for mastitis was related to a positive diagnosis of Strep. spp. after cow composite milk somatic cell count was omitted from the model. Presence of Streptococcus spp. was also related to culling specifically for mastitis, whereas culling for all reasons and treatment of clinical mastitis was not related to a positive culture of Strep. spp. Presence of coagulase-negative Staph. spp. or other pathogens was not associated with either of the outcome variables.
Key Words: cow • culling • mastitis • Staphylococcus aureus
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  O. Reksen, L. Solverod, and O. Osteras Relationships Between Milk Culture Results and Composite Milk Somatic Cell Counts in Norwegian Dairy Cattle J Dairy Sci, August 1, 2008; 91(8): 3102 - 3113. [Abstract] [Full Text] [PDF]
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R. G. M. Olde Riekerink, H. W. Barkema, D. F. Kelton, and D. T. Scholl Incidence Rate of Clinical Mastitis on Canadian Dairy Farms J Dairy Sci, April 1, 2008; 91(4): 1366 - 1377. [Abstract] [Full Text] [PDF]
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O. Reksen, L. Solverod, and O. Osteras Relationships Between Milk Culture Results and Milk Yield in Norwegian Dairy Cattle J Dairy Sci, October 1, 2007; 90(10): 4670 - 4678. [Abstract] [Full Text] [PDF]
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