Although a difficult therapeutic challenge, intramammary infections (IMI) caused by Staph aureus are not necessarily incurable. Depending on the herd, 30 to 70% of individual quarters may be cured during the dry period. Thus, if a little judgement isexercised in selection of cows as therapeutic targets, treatment can be reasonably effective and economical. The dry period offers the best time to administer therapy because milk withholding expenses are negligible, residue risks are reduced, and it isthe optimum time in the lactation cycle of the cow to enhance the synergy between antimicrobial activity and the immune system. It is potentially beneficially to administer systemic antimicrobials to dry cows in addition to intramammary therapy to enhance the elimination of IMI. This combination may be beneficial to lactating cows as well, however the costs of therapy and potential decreased efficacy should be considered carefully before treating lactating cows. Prolonged use of intramammary therapy (multiple regimens of labeled doses) may also increase efficacy, and vaccination prior to therapy may augment efficacy as well. However, cows with multiple infected quarters, or that are chronically infected (several months with elevated SCC) are poor therapeutic candidates. Additionally, it is highly recommended to use culture and susceptibility information to assist drug selection and dosing regimens.
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