Cyathostominae Egg Reappearance Period After Treatment With Major Horse Anthelmintics in Donkeys

The Egg Reappearance Period (ERP) is considered an early indicator of anthelmintic resistance. The aims of the present study were to determine the field efficacy and evaluate the ERP of four broad-spectrum anthelmintic drugs administered at horse dose rate in donkeys naturally infected by Cyathostominae. The trials were conducted in two farms (A and B). Forty-eight female crossbreed donkeys, 24 animals for each farm, were selected on the basis of Fecal Egg Count (FEC) > 300 eggs per gram and allocated to four treatment groups of six animals: pyrantel group (PYR), fenbendazole group (FBZ), ivermectin group (IVM), and moxidectin group (MOX). FEC was performed from the first to the 12th week after treatment. In the farm A at 2 weeks after treatment, the Fecal Egg Count Reduction Test (FECRT) showed high efficacy for all drugs (PYR 99.3%, FBZ 99.8, and IVM/MOX 100%), and ERP rates were not shorter than those expected. In the farm B at 2 weeks after treatment, FECRT showed high efficacy for IVM/MOX (100%), suspect resistance (86.3%), and resistance (83.9%) to PYR and FBZ, respectively; only in the MOX group a shortened ERP was detected (9 weeks). No adverse reactions were observed at clinical examination. The results demonstrate that the major anthelmintic classes, administered orally at horse dose, are effective and safe for treatment of Cyathostominae in donkeys, although resistance development is possible and could be correlated to the high treatment frequency and the extra-label use of anthelmintic licensed for ruminants. Furthermore, a shortened ERP may be the early indicator of developing anthelmintic resistance in donkeys.