Misconceptions regarding the use of post-treatment larval cultures for the identification of anthelmintic-resistant sheep nematodes

Abstract

Extract In a recent communication(1), it was suggested that, without a corresponding measure of their initial abundance also, the results of post-treatment larval cultures undertaken to determine the identities of those nematode genera surviving an- thelmintic treatment during faecal egg count reduction (FECR) testing in sheep were likely to be largely meaningless. Since then, the validity of this statement has been queried by a number of veterinary practitioners who appear to assume that, in cases of anthelmintic resistance, the only nematode genera that might be expected to be represented in post-treatment larval cultures are those that are drench-resistant. That this latter assumption is unfounded, however, may be illustrated by an analysis of post-treatment larval culture results obtained from 102 ovine anthelmintic resistance cases identified by FECR testing at the Batchelar Animal Health Laboratory.