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.

The impact of nematode parasitism of the digestive tract on milk output and milk quality was examined in dairy goats. In addition, the consequences of worm infection were compared in goats with different lactation performance (ie, with initial high or low milk production). Forty-eight goats in the second month of lactation were allotted equally to 2 groups. The first group was given 5,000 Haemonchus contortus and 20,000 Trichostrongylus colubriformis larvae. The 24 additional goats remained free of parasites. Parasitologic, serologic, and milk data were collected every 2 weeks for 5 months, and body condition of the goats was scored throughout the study. Results of strongyle egg count in feces, increase in pepsinogen values, and reduction in RBC count, PCV, and serum inorganic phosphate concentration indicated subclinical infection, This subclinical parasitism induced a decrease in body condition scoring and led to persistent decrease in milk yield, ranging from 2.5 to 10% reduction from control values. Changes in fat and protein contents were not detected. In contrast, the consequences of infection were more severe in the 6 goats with the highest milk production at the start of the study. Decrease in milk output ranged between 13.0 to 25.1%, and was associated with decrease in fat content. Comparison of the response to parasitism in the 6 goats with the highest lactation performance and the 6 goats with the lowest performance indicated differences be- tween both subgroups. According to parasitologic and pathologic data, high-producer goats had less resistance and/or resilience to infection associated with more severe consequences on milk production.