Sixty Najdi ram lambs, having an average weight of 23.5 kg, were used in an ad libitum feeding trial to assess protein and lipid retention in the tissue and their conversion efficiency in the body over a 120-day feeding period. Lambs were randomly allotted in a 2 x 3 factorial arrangement of two levels of dietary energy (concentrate: roughage ratio of 70:30 and 25:75) and three levels of broiler offal meal (BOM) supplementation [0, 50, and 100 g BOM kg-1 dry matter (DM)]. Lambs fed on high concentrate diets had higher (P < 0.01) values for metabolizable energy intake (MEi), retained energy as protein (REp), and retained energy as lipid (REf) and lower ME requirement for maintenance (Em) than lambs fed on high roughage diets. Increasing the level of BOM supplementation in the high concentrate diet was associated with concomitant increases (P < 0.01) in REp, REf and efficiency of retained lipid (Kf). The corresponding responses for the high roughage-fed lambs were a reduction (P < 0.01) in MEi and an improvement (P < 0.01) in REp and Kf.