A recently established Eragrostis curvula pasture 1, 1 ha in size at Hennops River in the Transvaal Highveld
was contaminated from 6 October 1976 until 20 May 1977 by 30 weaned Merinos, each infested with 7 000
infective larvae of H. contortus. On 2 November 1976 3 groups of weaned Merinos and again on 10 January 1977
a further group of Merinos were infested with 40 000 infective larvae of Trichostrongylus axei. From 19
November a single group of sheep, predosed with T. axei, and a control group grazed with the seeders for 8
weeks. After 6 weeks another group of sheep dosed with T. axei grazed with them, thus ensuring a 2-week
overlap. This continued until autumn, when the last groups were removed. Efficacy against challenge reached
Class C (>50% effective against total worm burdens of H. contortus in >50% of sheep) in early summer and
autumn, but only reached significant levels of either P<0,01 or P<0,05 in summer. Peak worm burdens in
controls were recorded in early autumn.
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