RESUMEN
In autumn 2000, a study was carried out on 25 dairy farms in the vicinity of Utrecht with the aim to estimate infectivity levels for nematode parasites in cows. On each farm, faecal samples were collected from 15 cows, blood samples from 5 of these and herbage samples from 2 cow pastures. Faecal examination demonstrated a variation between farms and within farms in faecal egg output with a mean number of 4 eggs/g faeces (EPG) and Ostertagia spp. and Cooperia oncophora being the dominant species. In 6 out of 21 farms examined, lungworm larvae were detected in at least 1 cow. Serum pepsinogen values and serology using ELISA's with crude adult Ostertagia, crude adult C. oncophora and a specific recombinant C. oncophora protein as antigens indicated low to moderate infection levels. Pasture infectivity levels varied between farms with again Ostertagia spp. and C. oncophora as the dominant larval types and correlated with the crude worm Ostertagia ELISA, the crude worm Cooperia ELISA and the pepsinogen values. Exposure levels were high enough to enable the possible occurrence of production losses on the majority of farms.