Twenty-four 10-month-old Polled Hereford heifers were inoculated sc with live cells of one of the following strains of Brucella abortus: S19 delta 31K (n = 4), S19 delta SOD (n = 4), RB51 (n = 4), and strain 19 (n = 6); controls (n = 6) were given saline solution. Heifers given the deletion mutants S19 delta 31K and S19 delta SOD, and those given strain 19 developed antibody responses to B abortus and cutaneous reactions to brucellin. Heifers given strain RB51 did not develop antibodies that reacted in the standard tube agglutination test, but sera reacted in tests, using an antibody dot-blot assay containing RB51 antigen. The S19 delta 31K and S19 delta SOD strains of B abortus isolated from lymph node tissue after vaccination did not differ genetically from the master stock strain. All heifers were bred naturally at 16 to 17 months of age, and were challenge-exposed intraconjunctivally with virulent B abortus strain 2308 during the fifth month of pregnancy. All vaccinated heifers were protected (ie, none aborted and none had B abortus isolated from their tissues after parturition). Calves born from vaccinated dams were free of B abortus. Antibody responses in heifers after challenge exposure were an indicator of immunity. All 5 control heifers (nonvaccinated) developed serum antibodies after challenge exposure; 3 aborted, and 1 delivered a small, weak calf at 8.5 months of gestation. Thus, live mutant strains of B abortus can induce protective immunity when given at 10 months of age, and strain RB51 is a strong candidate for further testing.

Effects of strategic anthelmintic treatment on pathophysiologic and immunologic changes induced by infection with Ostertagia ostertagi and Cooperia oncophora were studied in 2 groups, of 12 calves each: an infected group, inoculated with 200,000 mixed O ostertagi and C oncophora third-stage larvae (L3) on day 1; and an infected-treated group, similarly inoculated, but treated with ivermectin at 9 and 33 days. All calves were also inoculated at 12 weeks with Brucella abortus vaccine, at 13 weeks with bovine rhinotracheitis vaccine (bovine herpesvirus 1), and at 14 weeks with a soluble O ostertagi L3 extract, then were allowed to graze on a contaminated pasture. Four calves from each group were slaughtered at 7, 11, and 19 weeks of the study. Calves of the infected group had significantly (P < 0.05) lower weight gain than did those in the infected-treated group (60.90 kg vs 75.86 kg). They also had high plasma pepsinogen and serum gastrin values, and low serum albumin concentration from 2 or 4 weeks. Calves in the infected-treated group had steady weight gain and no significant changes in albumin and gastrin values. They also had less severe abomasal lesions and higher carcass yield. Compared with calves of the infected-treated group, those of the infected group had significantly (P < 0.05) lower blood lymphocyte reactivity to phytohemagglutinin at 14 and 16 weeks, to concanavalin A at 10 weeks, to pokeweed mitogen at 14 weeks, and to soluble O ostertagi L3 extract at 2, 4, and 14 weeks. They also had significantly (P < 0.05) lower IgG1 concentration to excretory-secretory antigens of the fourth-stage larvae of O ostertagi at 13, 18, and 19 weeks. In addition, they had significantly (P < 0.05) higher total mean eosinophil count. Antibody responses to B abortus and bovine herpesvirus 1, however, were not different between the 2 groups.