Effect of cool storage of faecal samples containing Haemonchus contortus eggs on the results of an in vitro egg development assay to test anthelmintic resistance.

An in vitro egg development assay was used to test the resistance of eggs from a benzimidazole susceptible and a resistant strain of Haemonchus contortus to four benzimidazoles. Storage of eggs contained in faecal samples at 4 degrees C for four, 24 or 72 hours did not appear to impair the results from the in vitro egg development assay or alter the LD50. Storage for one week, however, proved to be lethal for the eggs. The average LD50 values for thiabendazole, albendazole, mebendazole and cambendazole were 0.06, 0.07, 0.96 and 2.47 ppm for the susceptible strain. For the resistant strain the values averaged 0.26, 0.24, 1.07 and 5.11 ppm.