Variation in infection levels with gastrointestinal nematodes in first-year grazing calves in The Netherlands

ELISAs with crude adult Ostertagia and crude adult Cooperia antigens were used in a survey to monitor the levels of gastrointestinal nematode infections of 21 dairy calf herds. This survey was performed at the end of the grazing season of 1994 in The Netherlands. The mean extinction value of antibody levels of each herd was compared with those of four groups of reference sera of animals that had experienced moderate infection levels (one group), low infection levels (two groups) or no infection (permanently housed group). This was based on faecal examination, pasture larval counts, serum pepsinogen values and worm counts in tracer and main trial calves. The results of the ELISAs indicated a wide variation in infection levels. Most herds (90%) had infection levels equal to, or even lower than, those of the low infection-reference groups. Herds that had been moved every 2 or 3 weeks had lower infections than set stocked herds. The length of the grazing season showed a positive correlation with Ostertagia, but not Cooperia, antibody titres. There was no evident correlation between infection levels and anthelmintic treatment. The implications of these observations in relation to management and nematode control are discussed.