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Mastitis Infections Caused by Serratia

Dairy Pipeline: September 1998

Gerald M. (Jerry) Jones
Extension Dairy Scientist, Milk Quality and Milking Management
Virginia Tech
(540) 231-4764, e-mail:

There have been several inquiries about mastitis infections resulting from a bacteria called Serratia. According to Drs. Hogan and Smith, Ohio Agricultural Research and Development Center, Serratia bacteria are common inhabitants in water, soil, manure, bedding, and feed, but they are usually considered harmless residents of organic materials that can sometimes be implicated as causes of mastitis and other diseases. Such infections tend to be mild and chronic, and clinical signs have been sporadic. The incidence of new infection is greatest in summer and 62% of cases originate during the dry period, with 80% of those detected by 30 days into the dry period still present at calving. Outbreaks have been linked with contaminated water, bedding and litter, and teat dips but teat dips would have little to do with infections originating during the late dry period. More than half of infections became clinical. Average duration of infection was 131 days. Response to antibiotic treatment has been poor and would appear to be a waste of time and money. Dry cow therapy eliminated only 7% of infections, while lactation treatment eliminated 11%; 37% were cured spontaneously without treatment, culling eliminated another 17%, and 28% remained in the herd. Serratia bacteria are classified as gram-negative which means that they probably are not contagious and are not spread during the milking process. I would advise that little or no water be used to prep cows before milking but instead cows be predipped; teats be predipped but not washed prior to dry cow or lactation treatment; cows and heifers should calve outside whenever possible but not in a denuded lot; teat dippers should be emptied after every milking and washed in hot, soapy water; and wet, soiled bedding should be raked from the back third of free stalls every day.

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