PREVENTION OF PATHOPHYSIOLOGIC AND IMMUNOMODULATORY EFFECTS OF GASTROINTESTINAL NEMATODIASIS IN CALVES BY USE OF STRATEGIC ANTHELMINTIC TREATMENTS

Effects of strategic anthelmintic treatment on pathophysiologic and im munomologic changes induced by infection with Ostertagia ostertagi and Cooperia oncophora were studied in 2 groups, of 12 calves each: an in fected group, inoculated with 200,000 mixed O ostertagi and C oncophor a third-stage larvae (L(3)) on day 1; and an infected-treated group, s imilarly inoculated, but treated with ivermectin at 3 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 L(3) extract, then were allowed to graze on a contaminated pasture. Four calves from each gro up 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 di d those in the infected-treated group (60.90 kg vs 75.86 kg). They als o had high plasma pepsinogen and serum gastrin values, and low serum a lbumin concentration from 2 or 4 weeks. Calves in the infected-treated group had steady weight gain and no significant changes in albumin an d gastrin values. They also had less severe abomasal lesions and highe r carcass yield. Compared with calves of the infected-treated group, t hose of the infected group had significantly (P < 0.05) lower blood ly mphocyte reactivity to phytohemagglutinin at 14 and 16 weeks, to conca navalin A at 10 weeks, to pokeweed mitogen at 14 weeks, and to soluble O ostertagi L(3) extract at 2, 4, and 14 weeks. They also had signifi cantly (P < 0.05) lower IgG1 concentration to excretory-secretory anti gens 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 eos inophil count. Antibody responses to B abortus and bovine herpesvirus 1, however, were not different between the 2 groups.