Sheep grazed on natural pastures heavily infested with infective larvae of Haemonchus contortus. Sixty-eight
weaned Merinos were divided into 6 groups on Day 0 (23 November 1977), and on Day +14 (7 December)
79 Merinos were divided into 7 groups. There were 2 groups of undosed controls and other groups were either
dosed with infective larvae of Trichostrongylus axei (bovine strain) only on Days 0 and +14, or in combination
with H. contortus, or with subsequent doses of H. contortus, 28 days later. One group (Group 12) was dosed
with T. axei and treated with a subcutaneous injection of di-iodonitrophenol (DNP) on Day +14. With the
exception of 2 sheep, the sheep of the first 6 groups survived until slaughter in March and April 1978, while
many sheep (43) of the latter 7 groups died or were killed in extremis from March-May. T. axei dosed on 23
November (Day 0) protected Group 2 by >50% in >50% of sheep. In the latter 7 groups the best results were
achieved when DNP was combined with predosing with T. axei. The poor results were probably due either to
delayed predosing with T. axei or a massive challenge in the wettest summer on record.
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