Efficacy of a long-acting formulation of ivermectin against Psoroptes ovis(Hering, 1838) on cattle

A study was conducted in cattle experimentally infested with Psoroptes avis to compare the prophylactic control against P. ovis provided by a long-act ing injectable formulation of ivermectin to that of a commercially availabl e injectable formulation of doramectin. Thirty Holstein steers were used. A nimals were allocated by restricted randomization based on Day 0 body weigh t, forming six replicates of five animals each. Within each replicate, one animal was randomly allocated to one of the following treatment groups, wit h ivermectin and doramectin administered subcutaneously where indicated: (1 ) untreated controls; (2) ivermectin long-acting injectable (LAI) 630 mcg/k g, 56 days before challenge; (3) ivermectin LAI 630 mcg/kg, 42 days before challenge; (4) ivermectin LAI 630 mcg/kg, 35 days before challenge; or (5) doramectin 200 mcg/kg, 35 days before challenge. Animals were housed in ind ividual pens 1 week prior to treatment. All animals were experimentally inf ested with P. ovis mites in the area between the shoulders, on the same day . Live mites were counted in scrapings from mange lesions at 2 sites on eac h animal 14, 21 and 28 days after challenge. Live mites were found in 33, 6 7 and 83% of the untreated controls on each respective evaluation. No P. ov is mites were found in steers treated with ivermectin LAT. Those animals sh owed lower (P < 0.05) mite counts than untreated controls an evaluations co nducted 21 and 28 days after challenge. These results indicate that the ive rmectin long-acting injectable formulation prevents induced infestations by P. ovis for at least 56 days after treatment. Doramectin injectable formul ation, used at 200 mcg/kg, did not have a prophylactic effect 35 days after treatment. (C) 2001 Published by Elsevier Science B.V.