A field study on the efficacy of moxidectin and its egg reappearance period in donkeys naturally infected by Cyathostominae in Italy

Moxidectin (MOX) has a wide range of ecto-endoparasitic activity in many species including horses. There is a paucity of data on the efficacy of anthelmintics used in donkeys. The aims of the present study were to evaluate the field efficacy and Egg Reappearance Period (ERP) of MOX up to 84 days at horse dose against natural infection of Cyathostominae in donkeys. The trial was conducted in northern Italy, twenty-nine donkeys, were selected on the basis of faecal egg counts (FEC) > 300 EPG. Animals were treated on Day 0 with an oral gel containing MOX, at the manufacturer’s recommended horse dose (0.4mg/kg BW). FECs were performed on each donkey at least every fortnight during 84 days after treatment using a modified McMaster technique with a sensitivity 10 EPG. The efficacy and ERP values were determined following the AAEP Parasite Control Guidelines. The percentage reductions in FEC were 99.7% at the day 14, 99.5% at the day 28, 97.7% at the day 56 and 73.3% on day 84 post treatment. This trial demonstrates that MOX at horse dose was effective and safe for the treatment of Cyathostominae in donkeys, however with a shortened ERP this could be the first indication of developing anthelmintic resistance. Considering that the donkeys have a greater capacity to metabolize certain drugs compared with horses, a higher dosage or shorter intervals could be required for maintaining effective drug concentrations. The shorter ERP observed in the studied donkeys could be associated with a sub-therapeutic level of MOX.