Background -Ectoparasitism of ornamental birds, including captive species kept in zoos, represents a serious health problem. Up to 13 different species of lice have been reported to affect peacocks worldwide and heavy infestation may cause anaemia. Because of this, alternatives to the prevailing treatments have been sought including use of isoxazolines. This class of drugs has been used successfully in poultry without adverse effects on health or production.Objective -To evaluate the effect of afoxolaner on the peacock louse (Goniodes pavonis).Animals -Twenty-three peacocks (Pavo cristatus) with naturally occurring infestation with G. pavonis.Methods and materials -The peacocks were divided in two groups; one was treated once orally with 2.5 mg/kg afoxolaner and the other group received no treatment. Samples were collected using the acetate tape technique, for identification of lice by microscopy. Concomitantly, blood samples were taken to evaluate the haematocrit before and after the intervention.Results -Treatment with afoxolaner significantly decreased the number of peacocks positive for lice (P = 0.02) compared to the control group, in which the number of positive birds did not decrease. The haematocrit improved in the afoxolaner-treated group from a baseline of 46.4%-54.7% at 35 days post-treatment, whereas it decreased in untreated birds (44.6%-40.7%). No adverse effects attributed to afoxolaner treatment were observed.Conclusions and clinical importance -Oral administration of afoxolaner is an effective treatment for G. pavonis infestation of peacocks. AnimalsGoniodes pavonis lice were collected from 23 peacocks, which were transferred to the Parasitology and Microbiology laboratory of the