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.