(a) Mean titers of J5-specific antibodies in serum and milk samples from J5 vaccinates and controls just prior to intramammary challenge infusion with E. coli. Significant differences were higher serum IgG1 prechallenge (P = 0.003, ANOVA), higher serum IgG2 prechallenge (borderline significant at P = 0.07), and higher IgGs:IgM ratio in serum and milk (P = 0.02 and 0.03, respectively) in J5 vaccinates than in control cows. (b) Mean titers of J5-specific antibodies in serum and milk samples from J5 vaccinates and controls 12 h after intramammary challenge infusion with E. coli. Serum IgM was higher in controls than in J5 vaccinates (borderline significant at P = 0. 07, ANOVA). All other antibody titers and ratios were not significantly different in controls and vaccinates. (c) J5-specific antibodies in serum and milk 24 h after intramammary challenge infusion with E. coli. No significant differences between controls and vaccinates were observed.