Incidence of clinical mastitis was studied in 274 herds grouped in three categories by bulk milk somatic cell count (SCC). Mean incidence rate of clinical mastitis was 0.278, 0.257, and 0.252 cases per 365 cow-days at risk in herds with low (< or = 150,000), medium (150,000 to 250,000), and high (250,000 to 400,000 cells/ml) bulk milk SCC, respectively. The incidence rate of clinical mastitis was not different among the three categories. Variance in the incidence of clinical mastitis among herds increased as bulk milk SCC decreased. Clinical mastitis caused by Gram-negative pathogens, such as Escherichia coli, Klebsiella spp., or Pseudomonas spp., occurred more often in herds with a low bulk milk SCC. Clinical mastitis caused by Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus agalactiae occurred more often in herds with a high bulk milk SCC. Systemic signs of illness caused by clinical mastitis occurred more often in herds with a low bulk milk SCC. Both overall culling rate and culling rate for clinical mastitis were not different among groups catergorized by bulk milk SCC. In herds with a high bulk milk SCC, however, more cows that produced milk with a high SCC were culled. In herds with a low bulk milk SCC, more cows were culled for teat lesions, milkability, udder shape, fertility, and character than were cows in herds with a high bulk milk SCC. In herds with a low bulk milk SCC, cows were also culled more for export and production reasons.
The objective of this study was to determine the factors affecting somatic cell count (SCC), to estimate variance components of these factors, and to calculate and evaluate the thresholds for intramammary infection based on SCC. The infection status from 22,467 quarter milk samples from 544 cows in seven herds was determined. Infections status was the most important factor affecting SCC. The increase in SCC was more pronounced for major pathogens than for minor pathogens. Even after adjustment for infection status, the interaction between stage of lactation and parity was significant. For culture-negative samples within a lactation, the shape of the SCC curve was inversely related to the shape of the milk production curve. The shape of the SCC curve was flat for first lactation cows compared with the shape of the SCC curve for cows in subsequent lactations. The effect of clinical mastitis on SCC was significant. The use of SCC thresholds for specific parities and stages of lactation to detect intramammary infection improved quality parameters only slightly over a fixed threshold of 200,000 cells/ml.
Management practices associated with bulk milk somatic cell counts (SCC) were studied for 201 dairy herds grouped into three categories according to bulk milk SCC. The cumulative production of fat-corrected milk over 305 d of lactation and category for bulk milk SCC were highly correlated; herds within the low category had the highest milk production. Differences in bulk milk SCC among the categories were well explained by the management practices studied. This correlation was not only true for the difference between the high (250,000 to 400,000) and low (< or = 150,000) categories for bulk milk SCC but also for the difference between the medium (150,000 to 250,000) and low categories and the high and medium categories. Management practices that are known to be important for herds in the high category for bulk milk SCC, such as dry cow treatment, milking technique, postmilking teat disinfection, and antibiotic treatment of clinical mastitis, were also found to be important in the explanation of the difference between herds in the medium and low categories for bulk milk SCC. More attention was paid to hygiene for herds in the low category than for herds in the medium or high category. Supplementation of the diet with minerals occurred more frequently for cows in the low category for bulk milk SCC than for cows in the medium and high categories.
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.
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