Sainfoin is a fodder legume containing condensed tannins known to improve protein self-sufficiency, animal health and environment. In addition, anthelmintic effects have been demonstrated in vitro against cattle nematodes, and in vivo against nematodes of small ruminants, but in vivo effects against gastro-intestinal parasites (GIN) of cattle still remains to be proven. Thus, the aim of the present investigation was to determine the in vivo effects of sainfoin against the most important trichostrongylids of cattle the brown stomach worm Ostertagia ostertagi, and the intestinal worm Cooperia oncophora. Jersey male calves (2-4 months) reared indoor and GIN naive, were stratified for live weight and randomly allocated into a test group (SF; n=9) which was fed 80% sainfoin (cv. Perly) pellets and hay, and a control group (CO; n=6) fed hay and compound feed. Daily intake was monitored and protein/energy intake was equalized in both groups throughout the 8 weeks study period. After 2 weeks adaptation, calves were inoculated with approximately 10,000 O.ostertagi and 65,000 C.oncophora infective third-stage larvae. Individual weight gain was registered weekly, whereas eggs excretion, calculated as number of eggs per g of faecal dry matter (FECDM) was recorded 3 times a week. The calves were slaughtered and adult worms recovered 6 weeks post infection. FECDM was analysed by ANOVA using repeated measurements, and worm counts by Kruskal Wallis test. The mean FECDM was not significantly lower in the SF group (p>0,05). Worm counting of C. oncophora is ongoing, whereas mean worm counts of O. Ostertagi revealed 1,300±837 worms in the SF group and 2,500±870 in the CO groups (p<0,05).Thus, the preliminary results demonstrate an anthelmintic effect of sainfoin against establishment of O. Ostertagi in cattle.