Evidence of penetration of the bovine teat duct by Escherichia coli in the interval between milkings.

In 3 consecutive experiments, each using 20 cows, the application of Escherichia coli to teat ends after milking led to high rates of intramammary infection. These infections were not prevented by disinfection of the teats before milking, by the installation of shields in the short milk tubes of th milking cluster or by the use of an individual quarter milking cluster. Rates of infection were significantly lower when teat contamination was applied 1 h before milking compared to contamination applied immediately after milking. These data suggest that penetration of te teat duct by the E. coli occurred in the period between contamination and milking. Seventy four percent of infections occurred in hindquarters and there were variations in the susceptibility of cows to infection.