The objective of this study was to evaluate the performance of finishing Lacaune lambs fed Cratylia argentea hay as an alternative to Tifton 85 (Cynodon spp). Twenty-four Lacaune lambs aged between five and six months (average body weight [BW] 21.50 ± 3.38 kg) were arranged in a split-plot randomized block design. The plots consisted of different Cratylia to Tifton 85 hay proportions (0, 20%, 40%, or 100%, dry matter [DM] basis) as a roughage replacement in the total diet. The subplots represented two evaluation times, entitled “initial period” and “final period”, which consisted of the early seven days of total feces and urine collection, and the last seven days of the experiment, respectively. The lambs were blocked by weight with six replicates per treatment. The results show that the level of Tifton 85 replacement for Cratylia hay in the roughage portion of the lamb diet did not influence (P > 0.05) weight gain (WG), dry matter intake or dry matter digestibility; feed conversion, feed efficiency; and the evaluated nitrogen balance variables. Thus, the alternative legume successfully maintained animal performance of Tifton 85. The digestibility coefficient of neutral detergent fiber decreased linearly as Tifton 85 replacement for Cratylia level was increased, which probably happened due to the presence of highly lignified material within the Cratylia hay. In conclusion, Cratylia hay can be recommended as a feeding strategy for livestock production, especially in regions with unfavorable soil and climate, which requires greater inputs for the production of forage grasses, as Tifton 85.