WEIGHT-GAIN AND THE COURSE OF SOME ESTIMATORS OF GASTROINTESTINAL NEMATODE INFECTION IN CALVES DURING WINTER HOUSING IN RELATION TO THE LEVEL OF EXPOSURE DURING THE PREVIOUS GRAZING SEASON

In two experiments groups of calves were exposed to different levels a nd patterns of infection with Ostertagia spp. and Cooperia spp. The ex perimental design simulated the stereotypic pattern of herbage infesta tion, including a normal or a delayed midsummer increase, under condit ions of set-stocking. After this simulated 'first grazing season', cal ves were monitored throughout the subsequent winter housing period. No continuing negative effects of previous infection on growth performan ce were observed. Calves in all groups gained on average over 0.7 kg d ay(-1), irrespective of previous level of exposure. Differences betwee n the experiments with respect to either level or pattern of infection during the preceding 'first grazing season' were all, to a greater or lesser extent, reflected in faecal egg counts, pepsinogen values, gas trin values and antibody titres against Cooperia spp. or Ostertagia sp p. Depending on the time of sampling, pepsinogen values and antibody t itres against Ostertagia spp. particularly were useful variables for a ssessing differences in levels of infection to which groups of calves had been exposed.