Failure of Macrocyclic Lactones to Control Psoroptic Mange Infection in Feedlot and Grazing Beef Cattle

CANTÓN C.; FIEL, C.; STEFFAN, P.; MUCHIUT, S.; DOMINGUEZ, P.; VIRKEL, G.; SCHOFS, L.; LANUSSE, C.; ALVAREZ, L.; LIFSCHITZ, A.

Madison

Congreso; 27º Conference of the World Association for the Advancement of Veterinary Parasitology; 2019

World Association for the Advancement of Veterinary Parasitology (WAAVP)

The current work assessed the relationship between pharmacokinetic behavior and clinical efficacy of ivermectin (IVM) or doramectin (DRM) against natural Psoroptes ovis var. bovis infection in cattle. The study involved two trials (I and II) carried out on different beef cattle production systems, a feedlot (Trial I) and a grazing (Trial II) system. In Trial I, 40 mange-infected steers were allocated into 4 groups (n=10) and treated with a single (day 0) or repeated (days 0 and 7) subcutaneous injection of two different formulations of IVM (1%) at 0.2 mg/kg. In Trial II, 20 grazing calves with active mange infection were allocated into 2 groups (n=10) and treated with a single subcutaneous injection of either IVM (1%) or DRM (1%) at 0.2 mg/kg. Blood and skin samples were collected from 8 animals of each group to measure IVM/DRM concentrations by HPLC. Skin scraping samples were collected from each animal and mites were counted. In Trial I, the repeated administration of IVM increased the systemic availability and skin drug exposure compared to the single treatment (p0.05) in the P. ovis scores density were observed after single or repeated treatments. In Trial II, there was also a positive correlation between IVM or DRM concentrations in plasma and skin samples. Although IVM and DRM failed to obtain a complete parasitological cure, the efficacy of DRM was higher (80%) than those obtained by IVM (10%)(p