Resistance to a range of @entity9158 anthelmintics was investigated in 2 strains of Ostertagia spp. One strain (SR80) had been exposed to @entity18172 , @entity13486 and @entity18884 , the other strain (KR79) only to @entity18884 . Both strains showed a high degree of resistance to @entity3753 , @entity18172 , @entity13486 and @entity18884 , which had efficiencies of 11-38% and 0-60% against all developmental stages of SR80 and KR79, respectively. There was no significant reduction in the KR79 worm count by @entity18884 at 132 mg kg-1 given either as a single dose or divided into 12 equal portions, one administered every 6h. Nematodirus spp were also found to be resistant to all @entity13641 tested. Levamisole at 7 mg kg-1 and @entity69830 at 30 mg kg-1 had efficiences of 89 and 66%, respectively, against SR80 Ostertagia and 99 and 19% against Nematodirus, all but the last of these being significant reductions in worm burdens. The resistant SR80 Ostertagia occurred on a research station, but possibly originated from a property which 3 years earlier had supplied ewes to the station. The use of @entity9158 anthelmintics and subsequent grazing on worm-free pasture may have enhanced the level of resistance. A relationship was established between egg counts and adult worm counts 10 days post-treatment, which suggested that for Ostertagia the worm count could be predicted from the geometric mean egg count from about 10 animals. Thus, where an Ostertagia population is suspected of being resistant, an anthelmintic efficiency assay using pre- and post-treatment faecal egg counts should provide a satisfactory diagnostic procedure.

Resistance to XXXX anthelmintics in field strains of Ostertagia and Nematodirus in sheep.

@entity3753 :: ('MESH:D015766', 'Chemical') :: ['albendazole'] @entity18172 :: ('MESH:D005273', 'Chemical') :: ['fenbendazole'] @entity13641 :: ('MESH:D001562', 'Chemical') :: ['benzimidazoles'] @entity9158 :: ('MESH:C031000', 'Chemical') :: ['benzimidazole'] @entity13486 :: ('MESH:C011030', 'Chemical') :: ['oxfendazole'] @entity69830 :: ('MESH:C008897', 'Chemical') :: ['naphthalophos'] @entity18884 :: ('MESH:D013827', 'Chemical') :: ['thiabendazole']
@entity9158 :: (MESH:C031000,Chemical) :: ['benzimidazole']
