The effect of predosing calves with Trichostrongylus axei on subsequent challenge with Haemonchus placei

Twelve calves were dosed with 40 000 and a further 12 with 80 000 infective larvae of Trichostrongylus axei respectively. These 2 groups and a control group were subsequently dosed with 50 000 infective larvae of Haemonchus placei. Predosing with T. axei had no effect on the establishment of H. placei. It is postulated that the numbers of T. axei worms present were below the 'threshold' value necessary to protect the calves against challenge with H. placei.