Effect of coliform challenge at milking time on new udder infections

This project was designed to study rates of infection in udders of cows exposed to an Escherichia coli broth culture at milking time. Forty Holstein cows of varied stages of lactation were divided randomly into three treatment and one control group of ten cows each. The treatment groups were exposed for 3 wk to an Escherichia coli broth of 10(9) colony forming units per ml at milking time by either 1) dipping teat ends in broth before milking, 2) spraying the udder and leaving it dripping wet during milking, or 3) dipping teat ends in broth after milking. Eleven of 30 treated cows became infected in one or more quarters; all control cows remained uninfected. The infection rate of the three Escherichia coli-treated groups was higher than the controls. However, there was no difference among treated groups. Exposure to the broth culture of Escherichia 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 Escherichia coli broth.