Efficacy of in-feed formulation ivermectin against Psoroptes sp. in bighorn sheep.

Four Rocky Mountain bighorn sheep (Ovis canadensis canadensis) were experimentally inoculated with Psoroptes sp. of bighorn sheep origin by placing approximately 50 mites into each ear. Two sheep developed reproducing mite colonies and lesions consisting of alopecia, and exudative dermatitis with scabs on ears, face and neck. Three months after inoculation, all four sheep were treated with an in-feed formulation of ivermectin at a dosage of 1 mg/kg of body weight in a pelleted ration daily for seven consecutive days. Mites could not be detected on any of the sheep 1, 2, or 3 mo after treatment, and lesions on the affected sheep resolved within 6 to 8 wk after treatment. Thus, under these conditions, ivermectin was completely effective in eliminating the mites; it also was palatable and nontoxic. Use of ivermectin in pelleted feed for field treatment of psoroptic mange is encouraged.