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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

E. coli

Dairy Pipeline: October 1999

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

You keep hearing all these bad things about E. coli. Why? According to FDA's Bad Bug Book (, E. coli is a normal inhabitant of the intestines of all animals, including humans. Normally E. coli serves a useful function in the body by suppressing the growth of harmful bacterial species and by synthesizing appreciable amounts of vitamins.

There are several strains of E. coli. Serotype O157:H7 is a rare variety that produces large quantities of one or more related, potent toxins that cause severe damage to the lining of the intestine causing hemorrhagic colitis. Sound nasty? The illness is characterized by severe cramping or abdominal pain and diarrhea which is initially watery but can become grossly bloody. Occasionally vomiting occurs. The illness lasts for an average of 8 days.

Outbreaks can be either foodborne or waterborne. Many E. coli illness outbreaks have been traced to undercooked ground beef, some to unpasteurized milk, and others to water, cider, and vegetables. Dairy farms have been identified as reservoirs of E. coli. Prevalence of this bacterium on dairy farms is less than 5% and usually less than 1%. Of 3,570 fecal grab samples collected from 60 dairy herds, 10 had E. coli or 0.28%. But heifers and calves under 24 months of age are more likely to excrete E. coli (2.8%).

In one study, E. coli were found present in quite a few herds but only a small number of animals excreted the organisms which seem to grow in adverse environments. Gastrointestinal tracts of well-fed cattle were less conducive to growth of E. coli than cattle deprived of feed. Well managed dairy herds with low somatic cell counts often may experience problems with onsets of clinical mastitis with approximately 40-45% of the mastitis cases caused by environmental pathogens including E. coli. These bacteria are probably killed by pasteurization. These infections are usually associated with wet and dirty conditions that expose teat ends to bacterial contamination. Dirty housing and calving environments, certain types of bedding materials, improper or inadequate cow preparation for milking and milk letdown, and conditions within milking systems that create liner slips during milking are all factors that can potentially lead to mastitis.

Infections by environmental pathogens can be reduced by dry cow therapy, pre- and post-milking teat dipping, clean and dry teats and udders where hair has been removed, proper preparation for milking, milking system maintenance, fly control, and controlling mastitis in heifers at calving. Pathogen identification and treatment records are important.

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