The primary aim of this study was to compare the in vivo responses to orally administered doses of albendazole (5 mg/kg body weight) between experimentally infected sheep and goats. Fifty-four Improved Valachian lambs and 54 Saanen goat kids were split into six groups of nine animals. The sheep and goats were infected with larvae of the gastrointestinal nematode parasite Haemonchus contortus containing 10, 20, 30, 40, 60, and 80 % of the isotype-1 β-tubulin gene codon 200 alleles previously shown to be associated with benzimidazole (BZ)-resistance. All groups of goats generally had higher mean eggs per gram (EPG) before treatment, which was significant (p<0.05) only for the group with 80 % resistance alleles. An in vivo faecal egg reduction test (FECRT) was used to determine the efficacy of albendazole (ABZ) eight days after treatment. Anthelmintic treatment significantly reduced the EPGs in the groups with 10, 20, and 80 % resistance alleles in sheep and with 10, 20, 30, and 40 % resistance alleles in goats. Differences in efficacy between the sheep and goats after the application of doses of ABZ recommended for sheep mostly ranged from 2 % to 10 %. The largest variation was in the group infected with worms containing 60 % resistance alleles, where the efficacy was 13 % higher in goats. Our secondary aims were to evaluate the data obtained from an in vitro egg hatch test (EHT) in sheep and goats and to compare these data with the results from the isotype-1 β-tubulin gene codon 200 pyrosequencing and the FECRT. The percentages of the BZ-resistance alleles were comparable with the mean hatching obtained in the EHT and were also supported by the FECRT data for all groups. The results of the in vivo tests should be verified in the future using in vivo surveys conducted in mixed breeds and infections in multiple species.
