EFFICACY OF MOXIDECTIN 0.5-PERCENT POUR-ON AGAINST NATURALLY ACQUIREDNEMATODE INFECTIONS IN CATTLE

The efficacy of 0.5% moxidectin pour-on at two dosages was evaluated i n 30 cattle with naturally acquired gastrointestinal nematode infectio ns, The cattle were ranked according to pretreatment fecal egg counts and body weights, and were randomly assigned from replicates to three treatment groups, The mean number of trichostrongyle eggs in pretreatm ent fecal samples did not differ among the groups, Groups I and II rec eived 0.5% moxidectin pour-on at dosages of 0.25 mg moxidectin per kg body weight and 0.5 mg moxidectin per kg body weight, respectively, an d Group III cattle received moxidectin-free vehicle (control cattle), The cattle were euthanized by complete replicate 14 or 15 days posttre atment for recovery of nematodes and examination of the pour-on sites, Treatment with moxidectin was associated with a significant reduction in fecal trichostrongyle egg counts compared with the control cattle; efficacy was 99.7% and > 99.9% for cattle in Groups I and II, respect ively, Eleven species of adult nematodes (Haemonchus contortus, Haemon chus placei, Ostertagia ostertagi, Trichostrongylus axel, Trichostrong ylus colubriformis, Bunostomum phlebotomum, Cooperia oncophora, Cooper ia punctata, Nematodirus helvetianus, Oesophagostomum radiatum and Tri churis ovis) and 4th stage larvae of Ostertagia spp, and Trichostrongy lus spp, were present in sufficient numbers in control cattle to evalu ate the efficacy of moxidectin 0.5% pour-on. In all cases, treatment w as associated with a significant reduction in the number of nematodes recovered at necropsy, with the efficacy of both dosages exceeding 99. 9%. There were no significant differences in mean worm burdens or feca l egg counts between the two treated groups, and no adverse reactions were observed.