THE PROPHYLACTIC EFFECT OF A DRY-COW ANTIBIOTIC AGAINST STREPTOCOCCUS-UBERIS

The prophylactic use of a dry-cow antibiotic for reducing the incidenc e of mastitis due to Streptococcus uberis was studied in four seasonal ly calving dairy herds involving 378 cows. The treatment was a long-ac ting dry-cow antibiotic preparation administered immediately after the last milking of lactation. New intramammary infections were identifie d by comparing the bacteriological status of quarters at drying off wi th that after calving, or through manual udder palpation during the dr y period. The administration of dry-cow antibiotic to uninfected quart ers at drying off reduced the overall incidence of new infections with Streptococcus uberis from 12.3% for untreated quarters to 1.2% of qua rters (p < 0.01). The reduction was significant (p < 0.01) for both dr y-period and post-calving infections. The susceptibility of uninfected quarters to new infection by Streptococcus uberis appeared to be unre lated to the infection status of a cow at drying off. Clinical infecti ons during the dry period were most prevalent (97%) in quarters identi fied as having open teat canals. Fewer open teat canals (p < 0.05) wer e observed among antibiotic treated quarters over the first 4 weeks of the dry period. Treated quarters had a lower (p < 0.05) incidence of new clinical infection during the ensuing lactation and lower somatic cell counts. This did not affect production levels of milk, milk fat o r protein. The results clearly indicated a prophylactic benefit for th e dry cow antibiotic treatment against new Streptococcus uberis infect ions during the dry period.