Results
Effects of Immunization with FecA on Bacterial Challenge. The mean bacterial counts in milk from challenged quarters peaked at 9 hours after challenge for all treatment groups. The mean peak bacterial counts in milk from challenged quarters for FecA immunized cows was 790 cfu, 16,000 cfu for E. coli J5 immunized cows and 2,500 cfu for unimmunized controls. The mean peak rectal temperatures (mean + SE °C) for FecA immunized cows was 104.4, 106.3 for E. coli J5 immunized cows, and 106.2 for unimmunized controls. The FecA immunized cows tended to have lower clinical status compared with other treatment groups. The mean duration of clinical mastitis for FecA immunized cows was 11.7 hours, 35.3 hours for E. coli J5 immunized cows, and 37.1 hours for unimmunized controls. The average duration of infection for FecA immunized cows was 42.8 hours, 110.3 hours for E. coli J5 immunized cows, and 37.6 hours for unimmunized controls. Milk production did not differ among treatment groups. Milk production for all treatments was reduced approximately 20% on the day following challenge. Dry matter intake did not differ among treatment groups after challenge.
Antibody Titers. Immunizations increased serum and whey IgG titers against FecA compared with E. coli J5 vaccinated cows and unimmunized controls. The FecA immunization also increased serum IgM titers against FecA immediately prior to challenge. Immunoglobulin M titers in mammary secretions did not differ among treatments.
Immunization with FecA did not increase antibody titers against E. coli 727 cultured in either iron replete or iron limiting broth. Antibody titers against E. coli 727 tended to be greatest in sera and whey from cows immunized with E. coli J5.
Correlations among FecA titers and Clinical Signs. The severity of clinical signs following E. coli 727 challenge was associated with increasing antibody titers against FecA. Immunoglobulin G titers in mammary secretions against FecA immediately prior to challenge were negatively associated with peak rectal temperatures (r = -0.41). Serum IgG titers against FecA at 7 days after challenges were negatively associated with peak temperatures (r = -0.32) and with peak bacterial counts (r = -0.41).