Gain of lean and proportion of lean in the total gain were significantly higher for all-concentrate lambs than lambs receiving feed blocks. The reverse trend was obtained for fat gain and its proportion in the total gain. The source of nitrogen could explain this phenomenon. Furthermore, may be because the concentrate was highest in CP that lambs receiving this supplement had produced more muscle than those fed on feed block-supplemented diets. Data on the efficiency of energy utilization drawn from the literature may be inappropriate for comparison with data comparing conventional and alternative feed resources.