The experiment was carried out to evaluate the effects of malate supplementation (Rumalato, 160. g/kg disodium malate and 840. g/kg calcium malate) and starch source on digestibility and N and energy balances of fattening lambs fed concentrate and barley straw ad libitum. Four concentrates were prepared according to malate dose (0 versus 2. g/kg) and starch source (wheat versus a manioc-barley mixture). Eight individually lodged male Manchega lambs, were used in a double 4×4 Latin square design to evaluate nutrient digestibility and energy and N balances. Treatments were: W (wheat without malate), W. +. M (wheat with malate), MNB (manioc-barley without malate) and MNB. +. M (manioc-barley with malate). Malate did not affect dry matter (DM) intake and balances of energy and N, but slightly decreased digestibilities of DM and organic matter (OM; P<0.05) and in a larger extent that of acid detergent fiber (P<0.001). Lamb performances did not vary by adding malate but average daily gain and feed conversion ratio were numerically greater in lambs fed with malate and wheat based diets. Interactions between malate and source of starch were observed in intakes (concentrate and total DM, OM, starch and malate; P<0.05), as well as in N balance fractions (ingested, fecal, digested and retained; P<0.05). Compared to lambs fed MNB, lambs fed W had greater intake of N and malate (P<0.05), and lower fecal pH and feces consistency (P<0.05), digestibility of DM (P<0.01) and OM (P<0.001), and a tendency (P<0.10) to lower digestibility of neutral detergent fiber. Lambs fed MNB or MNB. +. M excreted less urinary and total N (P<0.05), and retained greater (P<0.05) proportion of N than those fed W or W. +. M. As a consequence they had lower losses of urinary energy (P<0.05) and tended to have greater digestible energy (P<0.10). In conclusion, malate had negative effects on digestibility of DM, OM and acid detergent fiber, and inconsistent performance results, depending on starch source. Manioc diets were more efficient than wheat diets in terms of N retention and digestibility of DM and OM in growing-fattening lambs. © 2012 Elsevier B.V.