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Abstract
In trials to assess the effectiveness of dry-cow therapy, 68% of untreated quarters having Staphylococcus aureus infections at drying-off time were still infected at the next lactation. In addition, new infections were observed in 26% of quarters. Dry-cow therapy with penicillin, novobiocin and neomycin eliminated 87% of infections from quarters. Dry-cow treatment with cephalonium was effective in eliminating infections only from quarters shedding S. aureus on 3 or fewer of the 4 sampling days before drying-off. The incidence of new infections in the dry period was 10% after the combined antibiotic therapy and 17% after cephalonium treatment.
The small number of quarters persistently shedding S. aureus after calving following dry-cow treatment resulted in reinfection of the herd; after 7 weeks of lactation, the number of infected quarters approximately equalled that before drying-off. In the present trial, dry-cow therapy was unable either to eliminate all infections, or to prevent reinfection or new infection during the dry period.