CHANGES OF ED(50) IN IN-VITRO EGG HATCH ASSAYS FOR DETECTION OF BENZIMIDAZOLE AND LEVAMISOLE RESISTANCE OF HAEMONCHUS-CONTORTUS AND OSTERTAGIA-CIRCUMCINTA IN LAMBS

Changes in ED(50) values were studied in egg hatch assays for benzimid azole and levamisole resistance. Eight lambs were infected with suscep tible and resistant strains of Haemonchus contortus and Ostertagia cir cumcincta. Faecal samples were taken three times per week for 70 days of the patent period and ED(50) values were determined using a test fo r benzimidazole resistance. Haemonchus contortus strains (HCR - resist ant and HCS susceptible) exhibited similar patterns of ED(50) values o ver time. This phenomenon was not observed in Ostertagia circumcincta strains (OCR - resistant and OCS susceptible). The coefficients of var iation in all strains were about of (13-18%). Also in comparing the va riability in resistant ratios (RR) the coefficient in Haemonchus conto rtus and Ostertagia circumcincta were 20 and 21% respectively. A test for determining levamisole resistance showed a considerable variation in values, with high differences in ED(50) values for HCR strain durin g patent period.