Abstract/Summary

Antibiotic regimens (intramammary antibiotic, penicillin-based parenteral treatment) and intramuscular oxytocin were tested for effectiveness against experimental infection by Streptococcus uberis with the following results from 54 animals: a) no treatment led to deterioration of infected quarters, requiring intervention within 48 h for cow health; b) aggressive intramammary antibiotic at every milking achieved 70% clinical cure in 3 d and 100% cure within 6 d; overall bacteriological cure was 80%; c) parenteral treatment alone used about 14 times as much antibiotic with 18% clinical cure in 3 d and 91% within 6 d; overall bacteriological cure was 80%; d) combination of aggressive intramammary and parenteral treatments achieved 61% clinical cure in 3 d and 100% within 6 d; overall bacteriological cure was 72%; e) intramammary antibiotic at labeled rates (1x for 3 d) achieved 27% clinical cure in 3 d but 91% within 6 d of treatment; overall bacteriological cure was 64%; f) use of oxytocin alone for 3 d failed to achieve clinical improvement with an increase in the severity of mastitis; g) combining oxytocin with labeled use of intramammary antibiotic (1x for 3 d) was unsuccessful: 0% clinical cures in 3 d, 10% in 6 d; significantly poorer than intramammary antibiotic alone. Extended treatment periods with parenteral or intramammary antibiotics resulted in positive inhibitory tests for milk from individual quarters up to 8 d after treatment. Aggressive intramammary antibiotic was the most effective treatment for fastest cure clinically and bacteriologically using least antibiotic.