EFFECT OF EARLY TREATMENT WITH IVERMECTIN AND DORAMECTIN ON THE DYNAMICS OF ANTIBODY-RESPONSE IN CATTLE NATURALLY INFESTED BY HYPODERMA-LINEATUM AND HYPODERMA-BOVIS

The field efficacy of two avermectins (ivermectin and doramectin) and the subsequent development of the antibody response were assessed in c ows naturally infested with first-instar larvae (L-1) of Hypoderma sp. Twenty-eight Frisian cows were randomly divided into three groups whi le the first-instar larvae were still in migration: Group 1 (G-C) untr eated control; Group 2 (G-Iv), treated with ivermectin injectable (0.2 mg kg(-1) body weight) and Group 3 (G-Dor), which received doramectin injectable (0.2 mg kg(-1) body weight). Serum antibody response was s tudied by an indirect ELISA test using, as antigen, the hypodermin C o btained from L-1 of H. lineatum. In treated animals no grubs were pres ent on the back at any time during the trial, whereas a variable numbe r of nodules were found in untreated animals. Both avermectins showed total efficacy against L-l of Hypoderma sp., and there were no local o r general reactions. in ivermectin-treated cattle serum antibody level s declined from one month p.t., while in those treated with doramectin they started to fall two weeks later, but no differences were found a mong both groups. On the other hand, G-C antibody levels progressively increased and remained high until December, when the first grubs beca me detectable on the back; after that, they began to decline. Early tr eatments against Hypoderma sp. have an influence on the results of ELI SA, so they must be considered to determine the most suitable time for blood sampling. (C) 1997 Elsevier Science B.V.