Persistence of the efficacy of a moxidectin gel on the establishment of cyathostominae in horses.

ABSTRACT

A controlled trial was carried out to evaluate the persistence of the effect against small strongyles of a 2 per cent moxidectin gel administered orally to foals at a dose rate of 0.4 mg/kg bodyweight. Five of nine helminth-free foals were treated on day 0, and the remaining four foals were used as controls. On days 0, 7, 14, 21 and 28 all nine foals were infected experimentally with 200,000 small strongyle larvae. Three treated and two control foals were necropsied on day 42 and the rest on day 43. Fourteen species of small or medium sized small strongyles were found in the control foals, 10 of them in all four. The mean rate of establishment of the infection was 27 per cent in the control foals and 7 per cent in the treated foals. The numbers of mucosal inhibited early L3 and late L3 were about equal in each group, but there were more than 10 times as many mucosal L4 in the control foals. No lumenal stages were recovered from the treated foals, whereas almost 50 per cent of the total burdens of the control foals consisted of these stages. The establishment of the infection was prevented by moxidectin treatment for at least two and possibly three weeks.