Our hypothesis was whether the residue of seed harvest from tropical grasses (Brachiaria sp. and Panicum sp.) as roughage source might result in the similar performance of lambs confined to obtain sustainability in agricultural and food systems by use of this by-product. This study was aimed to evaluate the effects of the residue of seed harvest (straw-hay) from tropical grasses as a roughage source in the feedlot lamb diet on intake, digestibility, performance, carcass characteristics and meat quality. The randomized block design used 36 lambs (six animals per treatment) distributed in six treatments arranged in individual cages on performance assay. The offered straw-hay did not influence nutrient intake and digestibility. Chewing was influenced by straw-hays. In addition, an effect was not observed on the length of the carcass, length of the leg, width and perimeter of the croup, depth of the chest or weight of the left half of the carcass. The averages of gammon, palette and neck yields were considered satisfactory, which may have been caused by the high content of neutral detergent fiber that was offered (511.4 g/Kg for Tupi and 617.6 g/Kg for Basilisk), and the weight of the palette and gammon can result in high commercial value. The meat characteristic was affected by a straw-hay. Diets containing residue of seed harvest from tropical grasses (Brachiaria sp. and Panicum sp.) as a roughage source did not have any effect on the dry matter and crude protein consumption and on the growth performance. So, we recommend the residue of seed harvest from tropical grasses as a fiber source to feedlot lamb diet.