The objective of this study was to evaluate the effect of the substitution of Tifton 85 hay (Cynodon spp.) with spineless cactus (Nopalea cochenillifera) on the intake, digestibility of nutrients and ingestive behaviour of sheep. Eight rumen-cannulated sheep were used, with an average body weight of 58.44 ± 13.5 kg. The treatments consisted of the replacement of Tifton 85 hay with cactus at levels of 0, 333, 666 and 1000 g/kg. Samples of food and leftovers were collected at the beginning of each trial period. Digestibility was estimated using indigestible acid detergent fibre. Ingestive behaviour was evaluated via scan sampling. The replacement of Tifton 85 hay with spineless cactus had a significant effect (P < 0.05) on the intake and digestibility of neutral detergent fibre and non-fibre carbohydrates. The rumination efficiency of neutral detergent fibre was not affected (P > 0.05) by the substitution of Tifton 85 hay with spineless cactus. However, plasma glucose, phosphorus and magnesium were linearly influenced by Tifton 85 hay replacement with spineless cactus. Therefore, spineless cactus can be used to replace up to 500 g/kg of Tifton 85 hay in complete diets for sheep.