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Orientador: Alessandro Francisco Talamini do Amarante / Banca: Cledson Augusto Garcia / Banca: Ivanete Susin / Banca: Kátia Denise Saraiva Bresciani / Banca: Reinaldo José da Silva / Abstract: Previous studies carried out in Brazil provided evidence that alternate grazing of a pasture by sheep and adult cattle can significantly reduce numbers of nematode parasites in sheep. An experiment was carried out from January/2004 to December/2005 in order to evaluate the control of sheep nematodes by using different alternate grazing strategies. An eight-paddock rotational grazing system was devised in which each paddock was grazed for 4 days, then spelled for 28 days. Six areas with 1.41 ha were subdivided into eight paddocks using electric fencing. Sixty six Ile de France ewes and 12 steers (more than 2-years-old) were randomly allocated in groups 1, 2 or 3 (22 sheep and 4 cattle per group). Three systems of grazing management were compared, each occupying two areas, a cattle area and a sheep area. In the systems 1, 2 and 3 the sheep and cattle were interchanged, respectively, every 32 days (animals of Group 1), every 96 days (animals of Group 2) or every 192 days (animals of Group 3). Monthly, faecal and blood samples were taken from each animal. Pasture samples were also collected from each paddock to determine the number of infective larvae per kg of dry matter (L3/kg DM). Tracer lambs were placed in each system to graze with the sheep of each group in three seasons of 2005 (summer, winter and spring). Then, these animals were slaughtered for identification of nematode species and estimation of worm burden. All cattle were also slaughtered with the same purpose. In the tracer lambs, Haemonchus contortus and Trichostrongylus colubriformis were the predominant nematodes, while in cattle, Haemonchus similis, Cooperia punctata and Oesophagostomum radiatum were the most important species. A considerable reduction in concentrations of third stage larvae on herbage occurred in areas that were grazed with cattle for 96 or 192 days. Cross infection between sheep... (Complete abstract click electronic access below) / Doutor