This study evaluated the effects of replacing corn with forage cactus in high-concentrate diets for lambs. We aimed that observe the performance, renal function, blood profile, and histomorphometry characteristics of feedlot lambs. Two experiments were conducted with non-castrated Santa In & ecirc;s lambs, with average body weights of 19.0 +/- 2.5 kg and 32.2 +/- 5.1, respectively, and a mean age of 120 days. The lambs were assigned to four treatments with increasing levels of corn and forage cactus (0, 250, 500, and 750 g/kg dry matter) in a randomized block design and completely randomized design. Higher concentrations of forage cactus in high non-fibrous carbohydrate diets compromised intake and apparent digestibility (P < 0.05), and reduced final body weight (P = 0.001). However, hydric balance improved with increased levels of forage cactus in the diet (P < 0.05). Changes in renal physiology included increased urine volume (P = 0.001), urinary pH (P = 0.001), and phosphorus excretion (P = 0.001). Blood metabolites related to energy and protein metabolism showed variations, and diets containing either forage cactus or corn grain modified the width of ruminal papillae and keratinized layers (P < 0.05), causing edema in rumen tissue. In summary, forage cactus can be included at up to 250 g/kg in feedlot lambs' diets, effectively supporting performance and providing a sustainable feeding strategy for Semi-arid regions, where water efficiency is essential.