Groups of Merino weaners were dosed with infective larvae of Trichostrongylus axei in numbers ranging from 20 000 - 50 000 and challenged 3 months later with 50 000 infective larvae of Haemonchus contortus. When half the dose of infective larvae of T. axei was given on Day 0 and the balance on Day + 14, efficacy against H. contortus was >60% in >60% of sheep (P < 0,1). A single dose of 40 000 or 50 000 infective larvae of T. axei was > 80% effective against H. contortus in > 80% of sheep (P<0,01).
Two doses of 20 000 infective larvae of T. axei followed by a challenge with H. contortus 31-33 days after the initial dose caused a reduction of > 50% in > 50% of sheep (P < 0, 1). This rose to > 60% in > 60% of sheep if the doses of 25 000 infective larvae of T. axei were followed by a challenge with H. contortus 45 days after the initial dose of T. axei. Most of the challenge doses of infective larvae of H. contortus were rejected within 3 days. Surviving worms were retarded in the 4th stage and only a few developed to the 5th or adult stage.