The effect of strategic anthelmintic treatment on the breeding performance and survival of ewes naturally infected with gastro-intestinal strongyles and protostrongylids.

In two trials, batches of ewes naturally infected with gastro-intestinal strongyles and protostrongylids (small lungworms) were treated with fenbendazole (10 mg/kg body weight) and morantel tartrate (8 mg/kg body weight) at strategic periods. In the first trial, treatment with fenbendazole during midgestation and early lactation, reduced miscarriages, stillbirths, mortality of ewes and their offspring. In the second trial, batches of ewes were treated wither with fenbendazole or with morantel tartrate or a combination of both at different strategic periods. In all the treated groups there were reductions in the mortality of ewes and their offspring which varied according to the regime of treatment and the nature of the anthelmintic used. The excessive mortality related to the presence of these parasites was 3.62% in ewes and 13.8 in lambs. For the former, Protostrongylids and gastro-intestinal strongyles played an equal role; Protostrongylids of ewes were the main cause of worm-induced mortality for the latter. The reduction in the output of strongyle eggs and lungworm larvae paralleled the breeding performance and mortality rate of animals.