Table 1.

Protection of calves immunized with A. marginale Florida outer membranes

AnimalaParameter to measure infectionb
Rickettsemia% Decrease in PCV (day)
Days to onsetMaximal % (day)
Immunized calves
 96BO5330.15 (39)32.6 (41)
 96BO6NAc 017.0 (36)
 96BO9NA013.0 (39)
Adjuvant controls
 96B19287.4 (36)47.1 (36)
 96B20285.3 (35)35.3 (35)
 96B21283.5 (37)41.7 (37)
  • a Calves 96BO5, 96BO6, and 96BO9 were immunized 4 times, by using 67 μg of Florida strain outer membrane protein per inoculation and saponin as an adjuvant. Control calves received saponin alone. Challenge was performed 6 months later with approximately 102 Florida strain organisms derived from an infected calf.

  • b Animals were observed for 46 days after inoculation of A. marginale. Giemsa-stained blood smears were examined daily for the presence of organisms. Data are presented as the day postchallenge when rickettsiae were first observed, the maximal level of rickettsemia and the day postchallenge when this level was reached, and the maximal percentage of decrease in PCV and the day postchallenge when this decrease was observed. The mean percentage of rickettsemia and percentage of decrease in PCV in immunized calves were significantly different (P < 0.05) from the mean percentage of rickettsemia and percentage of decrease in PCV in control calves.

  • c NA, not applicable.