Materials and Methods
Twenty-one cows were assigned to seven blocks of three cows based on the expected parturition date. Cows within a block were randomly assigned to three treatments: 1) FecA immunization, 2) E. coli J5 immunization, and 3) unimmunized control. Cows were immunized 3 times: 1) subcutaneous injection at 14 days prior to drying off, 2) intramammary infusion at 7 days after drying off, and 3) subcutaneous injection at 28 days after drying off.
The FecA was derived and purified from E. coli UT5600/pSV66 grown in iron limiting media. The FecA vaccine consisted of 400 µg in 5 ml of PBS and was emulsified in 5ml of Freund's incomplete adjuvant. The total volume of 10 ml of FecA vaccine was injected for the subcutaneous immunizations. Escherichia coli J5 vaccine consisted of 109 killed E. coli J5 cells/ml and water soluble adjuvant. Five ml of E. coli J5 vaccine was injected for the subcutaneous immunization. FecA and E. coli J5 intramammary infusions were administered as 2.5 ml into each quarter via the teat duct.
Escherichia coli 727 was used as the intramammary challenge strain. One uninfected mammary quarter of each experimental cow was challenged by infusion of approximately 60 colony-forming units (cfu) of the challenge strain. Cows were challenged between 13 to 31 days after parturition.