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Objective

To measure relative sensitivity and relative specificity for use of composite milk samples, compared with that of individual gland milk samples, for diagnosis of Staphylococcus aureus mastitis.

Animals

505 cows suspected of having subclinical mastitis. Of these cows, 172 were considered infected with Sta aureus, based on the results from individual gland samples.

Procedure

Composite and individual gland milk samples were collected from cows suspected of having subclinical mastitis, and results of bacteriologic culturing of samples from the same cow were compared. Results were interpreted at the cow level. Relative sensitivity and relative specificity for composite samples were computed from 2 × 2 tables, using results from individual gland samples as references.

Results

Relative sensitivity for use of composite milk samples in diagnosing Sta aureus mastitis was 0.63. The relative specificity was 0.98. Factors influencing the relative sensitivity for composite samples were the number of infected glands per cow, the amount of Sta aureus shedding from infected glands, and the proportion of the composite milk obtained from each gland.

Clinical Implications

Collecting composite instead of individual gland milk samples increases the number of false-negative results in diagnosing Sta aureus mastitis. By collecting consecutive samples from the same cow or by increasing the inoculum volume at culturing, this problem can be diminished. (J Am Med Assoc 1996; 208:1705-1708)

Free access
in Journal of the American Veterinary Medical Association

Summary:

In a set of data on farmer-observed clinical mastitis in cattle, all milk samples were scored with regard to milk color and milk texture (presence of flakes and viscosity). During a 1-year period, 1,106 milk samples were collected from 125 farms with a bulk milk somatic cell count < 150,000 cells/ml. The overall variation, the between-herd variation, and the within-herd variation of the scores were evaluated and compared with each other.

Differences between farmers were found for the scores on the visual characteristics per sample. However, these differences were not related to the reported number of cases of clinical mastitis per year. It was concluded that the diagnostic capability of farmers whose herds had low somatic cell counts did not have a negative influence on the validity of farmer-observed clinical mastitis incidence. However, care should be taken in herds with a low frequency of cases.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To evaluate the effect of natural udder infection with minor pathogens on subsequent natural infection with major pathogens.

Sample population

7 dairy herds with low bulk milk somatic cell count.

Procedure

During a 20-month prospective study, milk samples were collected from dairy cows at regular intervals and from quarters with clinical signs of mastitis. Incidence of intramammary infection was calculated in uninfected quarters and in quarters infected with minor pathogens. A within-cow, matched case-control analysis was used to evaluate the effect of minor pathogens on subsequent infection with major pathogens.

Results

Quarters infected with minor pathogens had higher somatic cell count than did uninfected quarters. In quarters infected with Corynebacterium bovis, the rate of infection with major pathogens was lower, whereas in quarters infected with coagulase-negative Micrococcaceae, the rate of infection with major pathogens was higher than that in uninfected quarters. From the within-cow comparison, it appeared that, in quarters infected with minor pathogens, infection with major pathogens was significantly lower than that in comparable control quarters not infected with minor pathogens.

Conclusions

Minor pathogens have a protective effect against infection with major pathogens. The protective effect of C bovis against subsequent infection with major pathogens appears to be greater than the effect of coagulase-negative Micrococcaceae. (Am J Vet Res 1997;58:17–22)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To study the epidemiology of clinical mastitis caused by Escherichia coli and Staphylococcus aureus by differentiating isolates with DNA fingerprinting techniques, using polymerase chain reaction.

Design

Milk samples were collected from cases of clinical mastitis in dairy cows. Escherichia coli and S aureus isolates from these cases were compared within and between cows and herds.

Sample Population

Seven dairy herds with an average bulk milk somatic cell count < 150,000/ml, and incidence of cows with clinical mastitis of > 25%/y.

Procedure

Chromosomal DNA was isolated from E coli and S aureus strains isolated from cases of clinical mastitis, and amplified by polymerase chain reaction, using enterobacterial repetitive intergenic consensus primers for E coli and a random amplified polymorphic DNA primer for S aureus. Escherichia coli and S aureus strains were identified and differentiated, using their DNA polymorphism pattern.

Results

Multiple E coli genotypes were found in each of the herds. Persistent infections with E coli were sporadic. Only a limited number of different S aureus genotypes was found in each of the herds studied. Recurrent cases of S aureus mastitis were found in 25% of quarters with clinical S aureus mastitis. Comparing S aureus isolates from different herds indicated that 1 S aureus genotype was most prevalent.

Conclusions

Because different quarters were infected with different genotypes, it was concluded that E coli is an environmental pathogen, and does not generally spread from quarter to quarter. The hypothesis that S aureus mastitis is a contagious disease, spreading from infected to uninfected quarters, could not be rejected. (Am J Vet Res 1996;57:39-42)

Free access
in American Journal of Veterinary Research