AbstractThe water balance and urinary parameters of lambs fed diets containing cactus cladodes varieties were evaluated. Thirty-six uncastrated male Santa Inês lambs (22.0 ± 2.9 kg initial body weight) were distributed in a completely randomized design, with three treatments and 12 replicates. The animals were fed a control diet (Tifton-85 hay as exclusive roughage), Miúda or Orelha de Elefante Mexicana (OEM) cactus-based diets. Urine samples were collected 45 days after the introduction of the tested diets, and voluntary water intake was measured over 10 days, during the experimental period. Diets containing Miúda or OEM cactus caused a reduction of 68.35 and 77.03% in voluntary water intake, respectively. In addition, the Miúda cactus cladodes caused urinary alkalinization (pH = 8.14) and reduction in the urinary excretion index (UEI) and on the fractional excretion rate (FER) of total calcium (Ca). The diets with OEM cactus cladodes caused higher oxalates intake (6.21 g/day) and increase in urinary volume. Regardless of the variety, there was a reduction in the urinary concentrations of urea, creatinine, total proteins, Ca, phosphorus (P), UEI of urea and P, as well as in FER of P, compared to the control diet. Urinary Mg content and UEI of uric acid and Mg increased and FER of P decreased by diets supplemented with different varieties of cactus cladodes. In conclusion, the cactus cladodes increased water intake and retention, and diuresis in lambs, altered urine parameters, without compromising kidney function.