Effect of Coliform Challenge at Milking Time on New Udder Infections

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Abstract
Rates of infection in cow udders exposed to an Escherichia coli broth culture at milking time were studied. Holstein cows (40) of varied stages of lactation were divided randomly into 3 treatment and 1 control group of 10 cows each. The treatment groups were exposed for 3 wk to an E. coli broth of 109 colony forming units/ml at milking time by either dipping teat ends in broth before milking, spraying the udder and leaving it dripping wet during milking, or dipping teat ends in broth after milking. Of 30 treated cows, 11 became infected in .gtoreq. 1 quarter; all control cows remained uninfected. The infection rate of the 3 E. coli-treated groups was higher than the controls. There was no difference among treated groups. Exposure to the broth culture of E. coli increased the infection rate, but the time at which the udder was exposed to the organisms was unimportant. All infections were of the same type with the same O and H group antigens as the E. coli broth.