Dry cow
therapy, or
antibiotic treatment at end of lactation, is used to eliminate intramammary
infections and prevent new
infections during the dry period. It is one part of a total management system recommended in controlling intramammary
infections in the dairy cow. Public health concerns advise prudent use of
antibiotics, as their use may promote bacterial antibiotic resistance and leave
antibiotic residues in the food chain. The effects of dry cow treatment and no treatment were compared, on new intramammary
infections and clinical
mastitis within two low cell count herds and two herds undergoing conversion to organic farming. The results will inform those restricting their use of dry cow
therapy on the additional risk of new intramammary
infection and aid in development of alternative management strategies. No cases of clinical
mastitis in the dry period were observed in treated cows, whereas in the untreated groups a significant number were observed. Significantly more new
infections at calving were found in the untreated group in all herds. In those quarters where
infections were first detected at calving, the incidence of clinical
mastitis was significantly greater in the untreated group in all herds. Clinical
mastitis detection was significantly lower in organic herds. Untreated quarters infected at drying with Corynebacterium spp. or
coagulase-negative staphylococci were found to have an increased risk of new
infection by Streptococcus uberis or coliform bacteria. It can be concluded that dry cow
therapy continues to lower significantly the rate of new dry period intramammary
infection in herds with elevated somatic cell counts and a high prevalence of
infection.