The conventional lungworm vaccination schedule, requiring a minimum age of eight weeks, a four-week interval between doses and a further interval of not less than two weeks before turnout, was compared with a modified schedule in which the vaccine was given to calves at six and eight weeks old followed by a turnout immediately after the second dose. The control group consisted of unvaccinated calves, half of which corresponded in age to the conventional and half to the modified vaccination group. All groups were turned out to the same pasture area on May 13 with five calves which were artificially infected with Dictyocaulus viviparus so as to ensure adequate pasture challenge. Challenge caused only mild clinical signs in the vaccinated calves but caused severe husk with two fatalities in the controls. Respiratory rates and faeces larval counts for the vaccinated groups were significantly lower than for the control group and, in the main, not significantly affected by vaccination schedule. The vaccinated groups gained more weight than their respective controls of corresponding age and significantly so for both groups during the period when dictyocaulus infection exerted maximum effect. In this experiment, the modified schedule was as effective as the conventional although delayed challenge precluded a satisfactory test for the effect of turnout immediately after the second dose of vaccine. In a repeat experiment involving apparently a very severe pasture challenge, calves vaccinated at six and eight weeks old showed markedly less resistance than those vaccinated according to the conventional schedule. Probable reasons for the difference in outcome are considered.

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Based on faecal larval counts, respiratory rates and live-weight gains, the anthelmintics levamisole and fenbendazole were equally efficacious against primary infection with Dictyocaulus viviparus in calves. Calves that were treated with levamisole or fenbendazole resisted the live-weight depressing impact of reinfection. Treatment somewhat impaired resistance to establishment of the secondary challenge as determined at necropsy. However, compared with previously uninfected controls, the treated animals harboured significantly fewer D viviparus, showing that they still strongly resisted reinfecting worms becoming established. The animal responses measured did not demonstrate any difference between levamisole and fenbendazole in relation to efficacy or to effect on resistance.

Under experimental conditions, fenbendazole given at doses of 0.4 and 1.0 mg/kg body weight suppressed calves' faecal output of Ostertagia and Cooperia species eggs and Dictyocaulus viviparus larvae. Both dose levels were given in the form of small daily drenches and the higher level showed greater efficacy. In a grazing experiment, medication with fenbendazole at 1.0 mg/kg/day administered intermittently to calves using an automatic dose dispenser almost completely suppressed the output of trichostrongylid eggs. As a result, infection on the pasture and in the calves remained at a low level throughout the grazing season. By contrast, control pasture and control calves showed rather heavy infection from mid-August onwards with significantly lower weight gains and widespread signs of parasitic gastroenteritis. At post mortem examination of representative calves from each group in November, the medicated animals had 99 per cent less Ostertagia species, whether adults or larvae arrested at the early fourth stage, and 95 per cent less Cooperia species compared with controls. Medication in the drinking water suppressed the faecal output of D viviparus larvae for most of the grazing season by comparison with the controls but the medicated calves became infected with this parasite towards the end of the season. Until this problem is overcome, precautions against parasitic bronchitis are advised when this system of medication is adopted.