Experimental intramammary infection of the dairy cow with Escherichia coli during the nonlactating period.

The nonlactating mammary gland was experimentally inoculated with Escherichia coli. During the first half of the nonlactating period, 32% of 34 inoculated glands were temporarily infected. All intramammary infections were eradicated by the cow without therapy and no signs of mastitis were observed. During the 30 days before parturition occurred, 88% of 42 inoculated glands in the cows became infected. Twenty-three intramammary infections were eradicated by the cow and infection in 14 glands persisted after parturition occurred. Peracute toxic mastitis occurred in those cows with infected glands.