Variations in the susceptibility of lactating and non-lactating bovine udders to infection when infused with Escherichia coli

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Abstract
Small numbers of E. coli were infused into lactating and non-lactating udders. Twelve of the 17 lactating quarters infused became infected, and all 12 showed clinical symptoms of udder disease. The 5 lactating quarters which did not become infected all had pre-infusion somatic cell counts > 300,000 cells/ml milk, while all the quarters which became infected had cell counts < 300,000 cells/ml milk, E. coli was subsequently recovered from only 6 of the 16 non-lactating quarters infused. In only 2 of these quarters did clinical infection follow, both quarters being in a cow infused 2 days before calving. The remaining 4 quarters from which E. coli was recovered were all negative within 5 days of infusion. These differences in susceptibility are discussed, particularly with reference to the frequent occurrence of coliform mastitis at and shortly after calving.