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Summary

Recovery of cows (n = 61) with mastitis caused by gram-negative bacteria and treated systemically with an antibiotic (gentamicin) to which the bacteria were susceptible in vitro, was compared with recovery of cows (n = 13) with similar infections treated with a systemically administered antibiotic (erythromycin) to which the bacteria were resistant in vitro or with recovery of cows (n = 12) not given an antibiotic systemically. In the first part of the study, cows were selected for treatment groups by use of a diagnostic scheme designed to predict whether the mastitis was caused by gram-negative or gram-positive bacteria. In the second part of the study, all cows were treated without systemic administration of an antibiotic.

Significant difference was not observed in the outcome of the disease between cows given gentamicin and cows of the other 2 treatment groups at 24 hours or at 4 weeks after treatment. At 24 hours after initial treatment, 71.9% of cows treated with gentamicin, 92.3% of those treated with erythromycin, and 45.5% not treated systemically had improved appetite. At 4 weeks after initial treatment, of the cows treated with gentamicin, 11.5% died; in 32.8%, lactation ceased in the affected mammary gland; in 21.3%, lactation was decreased in the affected gland; and 34.4% returned to normal lactation and health. Of cows treated with erythromycin, none died; in 23%, lactation ceased in the affected mammary gland; in 23%, lactation decreased in the affected gland; and 54% returned to normal lactation and health. Of cows not treated systemically, 8% died; in 50%, lactation ceased in the affected mammary gland; in 8%, lactation decreased in the affected gland; and 33% returned to normal lactation and health. Differences between cows treated with gentamicin and the other 2 groups of cows were not statistically significant.

Free access
in Journal of the American Veterinary Medical Association

Summary

The accuracy of a scheme for predicting the gram-staining reaction of organisms causing bovine mastitis in cows with systemic signs of disease (anorexia) was evaluated over 1 year. Criteria for making the predictions included: season of year, stage of lactation, appearance of milk, detection and duration of teat injuries, and milk odor. It was possible to determine the cause by microbiologic culture of specimens from 136 of the 147 cows of the study. Of 78 infections caused by gram-negative (mostly coliform) organisms, 62 (79%) were predicted accurately to be caused by gram-negative organisms. Of 57 infections caused by gram-positive organisms, 45 (79%) were predicted correctly to be caused by gram-positive organisms. Correctly predicted as gram-positive organisms causing infection were: Actinomyces pyogenes in 20 of 21 (95%) cows; Staphylococcus sp in 14 of 22 (64%) cows; Streptococcus sp in 10 of 13 (77%) cows and Bacillus sp in 1 cow. Overall accuracy, in those instances when bacteria were isolated (136 cows), was 78%.

Free access
in Journal of the American Veterinary Medical Association