In order to study the effect of yeast incorporated « Saccharomyces cervisiae » (LEVUCELL Sc 10. ME) at different doses in concentrated feed on growth performance of lambs of the Black Thibar breed. Forty-five (45) lambs were divided into three homogeneous groups for live body weight (17.08 ± 2.49 Kg) and for age (147 ± 12 days). Lambs were fed a basic ration of oat hay ad libitum and 400 g /lamb/d of concentrate feed during a 78 days trial period. Lambs in each group received food concentrates differing in the amount of yeast. The control group (C), concentrate feed contains no yeast; the group (DR) with concentrated feed contains 0.4 g of yeast and group (DD) in which the food concentrate contains 0.8 g of yeast. The intake of dry matter of the basal diet was 24.4; 22.4 and 22.0g DM/Kg W 0. 75 for groups C, DR and DD respectively. The average live weight was 25.82; 25.92 and 26.06 kg for groups C, DR and DD respectively. The average weight gain was 148.54; 144.3 and 149.67 g/d groups (C), (DR) and (DD) respectively. The consumption index was 4.16; 3.6 and 3.15 kg DM/kg) groups (C), (DR) and (DD) respectively. In conclusion, the group (DD) has relatively high performances than the group (DR). 1354299897.php