Anthelmintic efficacy of netobimin against naturally acquired gastrointestinal nematodes in yearling heifers.

The efficacy of netobimin (Coded SCH 32481, Schering Corporation) in removing naturally acquired gastrointestinal nematode infections was evaluated in 10 treated and 10 untreated (control) yearling beef heifers. The anthelmintic was administered as an oral drench at a dose level of 7.5 mg kg-1 body weight. Fecal egg per gram (EPG) counts were reduced with netobimin by 98% (P less than or equal to 0.01) at both 1 and 2 weeks post-treatment (PT). The compound was highly effective in removing Oesophagostomum radiatum (100% at P less than or equal to 0.01), Cooperia spp. (97.66% at P less than or equal to 0.01) and Nematodirus helvetianus (100%, although not significant), but was ineffective against immature Ostertagia ostertagi (3.19%) and only moderately effective against adult forms (66.14% at P less than or equal to 0.05). The low efficacy against adult O. ostertagi was partially attributed to the maturation of fourth-stage larvae, not removed by the 7.5 mg kg-1 treatment, during the 14-day treatment-slaughter interval. Efficacy against Trichuris spp. could not be evaluated due to low levels and unequal numbers of worms recovered in the groups. The overall efficacy against adult species, excluding Trichuris spp., was 67.40% (P less than or equal to 0.05). No adverse reactions or signs of toxicosis were observed in heifers treated with netobimin.