PERSISTENCE OF THE EFFICACY OF DORAMECTIN AGAINST OSTERTAGIA-OSTERTAGI AND COOPERIA-ONCOPHORA IN CATTLE

The persistence of the efficacy of doramectin injectable against Oster tagia ostertagi and Cooperia oncophora was evaluated in two studies in calves, In both, the calves were allocated to six groups of six. Calv es in the first control group (C1) and first treated group (T1) receiv ed a daily infection of 200 L3 of O ostertagi and 200 L3 of C oncophor a; the calves in groups ct and T2 received a daily infection of 1000 L 3 of each species, and groups C3 and T3 received 10,000 L3 of each spe cies per day. The calves in the three treated groups each received 0.2 mg/kg doramectin injectable on day 0, In the first study, the calves were infected for 21 days with Cooperia and for 28 days with Ostertagi a, and they were slaughtered on day 33, In the second study, the calve s were infected for 21 days with both species, the infections with Coo peria and Ostertagia starting from eight and 15 days, respectively, af ter the treatment, and the animals were slaughtered on day 40, The cal culation of the persistence of the activity of doramectin was based on its efficacy against the different developmental and adult stages of the two parasites. The data from both studies indicated that the effic acy of doramectin against Ostertagia persisted for at least five weeks , but no conclusions could be drawn about the effect of the size of th e infective doses on the persistence of the activity, In contrast, the Cooperia worm counts from the second study suggested that the efficac y of doramectin against Cooperia persisted for at least four weeks whe n the calves were exposed to a low or moderate infection level, wherea s at the highest infection level it persisted for between three and fo ur weeks.