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Canadian Bovine Mastitis Research Network

All about Mastitis I Treatment and Antimicrobial Resistance

Staph. aureus Infections Respond Poorly to Treatment

Staphylococcus aureus is probably the most common cause of contagious mastitis in dairy herds. It is considered contagious because the organisms are easily spread from infected quarters to other quarters and cows.

The primary source of this organism is milk from infected cows. Transmission of the organisms to uninfected cows and quarters occurs mainly at milking time. Objects that may transmit bacteria include contaminated milking units, common sponges and towels, milkers' hands, strip cups, and other items used during milking.

Mastitis caused by Staph. aureus produces tissue damage and decreased milk production with reported losses of 45% per quarter and 15% per infected cow. Additional losses include recurring mild clinical mastitis and occasionally, a life-threatening gangrenous mastitis at calving.
High bacteria counts in bulk tank milk are usually not seen with Staph. aureus mastitis. However, as the number of infected cows increases, the bulk tank milk somatic cell count increases, resulting in decreased milk quality.
Early treatment of new infections can be effective; however, chronically infected cows respond poorly to lactational therapy. Dry cow treatment may give better results, but chronic infections can persist into subsequent lactations. Infected cows should be identified, segregated, and milked last at every milking. These animals should be culled when daily feed costs exceed income from milk production.
To prevent the spread of Staph. aureus mastitis, milk from infected cows should never come in contact with uninfected cows. Backflushing of the milking unit may help reduce contamination of the claw and liners. Individual single-use paper or cloth towels should be used to clean and dry the udder. An effective post-milking teat dip must be applied immediately after every milking.
It is economically practical and possible to eradicate Staph. aureus mastitis from a herd. There are dairies who have achieved a "Staph. aureus-free" status. To accomplish this, every infected cow must be identified, and the clean herd closely monitored by DHIA individual somatic cell counts or milk culturing. In the average herd, Staph. aureus eradication will take 2 or 3 years with careful mastitis control management.

Source : www.nmconline.org

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