Resilience of second year grazing cattle to parasitic gastroenteritis following negligible to moderate exposure to gastrointestinal nematode infections in their first year

The influence of gastrointestinal nematode infections on performance of fou r groups of female Holstein Friesian calves was monitored until the end of the second grazing season (SGS). In the first year three groups were grazed and one group (G4) was permanently housed. General and grazing management during the first grazing season (FGS) was arranged such that G1 acquired mo derate infections, G2 low infections and G3 very low infections with gastro intestinal nematodes. These infections were monitored through faecal egg co unts, differentiation of faecal larval cultures, pasture larval counts, ser um pepsinogen values, ELISA with a recombinant Cooperia ancophora protein, weight gain, tracer worm counts and sentinel worm counts. In 1998 all four groups were grazed together as one herd from 23 April to 26 October and inf ections were monitored with the same techniques with the exception of senti nel calves. In the FGS weight gain was higher in G4 than in the other group s and higher in G3 (28.6 kg) than in GI. Weight gain of G2 was intermediate to G1 and G3 but did not significantly differ from either group. In the SGS weight gain in G4 was far less than in any other group and the m ean weight at the end of the experiment was 41.9, 38.6 and 50.9 kg lower th an G3, GL and G2, respectively. Though no significant differences were obse rved between G1, G2 and G3 at the end of the experiment it was obvious that the weight gain advantage of G3 over G1 at the end of the FGS had disappea red. Parasitological and serological findings in the SGS indicated that G3 and G 4 had build up less immunity during the FGS compared to G1 and G2. The conclusion of the experiment is that resilience to parasitic gastroente ritis in the SGS depends on the level of exposure to nematodes in the FGS. However, problems with poor weight gain only will be expected when exposure is very low in the FGS and high in the SGS. (C) 2000 Elsevier Science B.V. All rights reserved.