Studies on Haemonchus contortus. VI. Attempts to stimulate immunity to abomasal trichostrongylids in Merino sheep.

Two doses of infective larvae of 20 000 Trichostrongylus axei, dosed to Merino lambs at an interval of 14 days and subsequently challenged with Ostertagia circumcincta, caused a significant reduction (P less than 0.01) in the establishment of 5th and adult stages of the latter. T. axei was unable to protect Merino sheep against homologous challenge nor was Haemonchus contortus a successful vaccine against challenge with the same species. The vaccinated group showed a reduction (P less than 0,025) only in 5th and adult H. contortus, but not in the total worm burdens.