The residual anthelmintic efficacy of moxidectin against selected nematodes affecting sheep.

Determination of the residual anthelmintic efficacy in sheep of an oral formulation of moxidectin at a dosage rate of 0.2 mg kg-1 was evaluated 27-29 (mean: 28) d after dosing and that of the injectable formulation of moxidectin at a dosage rate of 0.2 mg kg-1 at 27-29 (mean: 28) and 34-36 (mean: 35) d post-treatment. The injectable formulation was more than 80% effective in more than 80% of treated sheep against a third larval stage challenge of Haemonchus contortus, Teladorsagia (Ostertagia) circumcincta, Gaigeria pachyscelis and Oesophagostomum columbianum at both 28 and 35 d post-treatment. The oral formulation on the other hand was equally effective against a third larval stage challenge of G. pachysce1is at 28 d post-treatment and more than 60% effective in more than 60% of treated sheep against a third larval stage challenge at 28 d post-treatment of H. contortus, T. circumcincta and O. columbianum.

Efficacy of moxidectin against internal parasites of sheep.

The efficacy of injectable and oral formulations of moxidectin, at a dosage of 0.2 mg kg -1 live mass was evaluated by the non-parametric method (NPM) against the most common internal parasites of sheep in 9 trials involving a total of 201 sheep. Both formulations obtained an A classification (more than 80% effective in more than 80% of the treated animals) against the third (L3) and fourth (L4) larval and adult stages of Haemonchus contortus, Teladorsagia circumcineta, Trichostrongylus colubriformis, Gaigeria pachyscelis, Chabertia ovina, Oesophagostomum columbianum and Dictyocaulus filaria, and L3 Nematodirus spathiger. The injectable formulation was similarly effective against L4 Strongyloides papillosus and the oral formulation against L4 N. spathiger and adult S. papillosus and N. spathiger. In contrast, a B classification (more than 60% effective in more than 60% of the treated animals) was obtained by the oral formulation against L4 of S. papillosus and by the injectable formulation against L4 and adult N. spathigher. Both formulations were ineffective against L3 S. papillosus, and the oral formulation also against the adults of this species.