Dynamics of pasture contamination by gastrointestinal nematodes of cattle under extensive management systems: proposal for strategic control

An epidemiological study of gastrointestinal nematode parasitism in beef ca ttle in mountainous areas of Spain was performed. The dynamics of contamina tion with gastrointestinal nematode larvae of Pyrenean pastures was studied over four years at five areas at different altitudes (900 m to 2100 m), gr azed by animals according to traditional systems of beef cattle in mountain ous areas. Grass samples were taken every two weeks and larval differentiat ion was performed. Worm egg counts of grazing animals were assessed in cows , heifers and calves. A consistent seasonal pattern of infective larvae on pasture through the study was observed. In hay meadows, located below 1000 m, infective larvae were found from the end of October until June of the fo llowing year. At higher altitudes (1200-2100 m), a bimodal pattern of pastu re larvae contamination was observed with increases in late spring (March-J une) and in late autumn (September-November). Ostertagia spp., Cooperia spp ., Trichostrongylus spp., Oesophagostomum spp., and Nematodirus spp. were f ound, with Ostertagia spp. being the most frequently found, followed by Coo peria spp. The highest increase of larval contamination in autumn coincided with the grazing of animals in hay meadows. This elevated autumn larval po pulation had a very important epidemiological role because these larvae rem ained as overwintered larvae until the following grazing season, starting t he cycle of contamination of the animals. (C) 1999 Elsevier Science B.V. Al l rights reserved.