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Simple Summary: Because the spineless cactus has a low dry matter, neutral detergent fiber and crude protein content, its use alone is not recommended, and it should be combined with other bulky food sources, such as gliricidia, pornunça and buffel grass, as they are found in abundance in semi-arid regions and nutritionally complement the cactus. Thus, a homogeneous mixture of spineless cactus-based silage in combination with these tropical forages can reduce the selection of components by animals, benefiting their performance and reducing costs compared to their conventional diet, given the more efficient intake. This study investigated the chemical composition, fractionation of carbohydrates and proteins, ruminal degradation kinetics and in vitro gas production of silages composed of cactus and tropical forage plants and their potential use as exclusive feed for sheep. Mixed spineless cactus silages with tropical forages have positive effects on ruminal degradation, digestibility and gas production. Mixed spineless cactus silage with tropical forages can be used as exclusive feed for sheep and can replace corn silage in diet composition. The aim was to evaluate the chemical composition, carbohydrates, protein fractionation and in vitro gas production of silages composed of spineless cactus and tropical forages and their effect on sheep performance. Treatments consisted of silages: corn silage (CS), spineless cactus silage (SCS), spineless cactus + gliricidia (SCG), spineless cactus + buffel grass silage (SCBG) and spineless cactus + pornunça (SCP). Silos were opened 60 days after ensiling, and analyses were carried out. The digestibility test lasted for 36 days, with eight animals per treatment. A completely randomized design was adopted. Considering carbohydrate fractionation, CS, SCS and SCBG silages had higher total carbohydrate content (p = 0.001). The SCS silage presented a higher A + B1 fraction (p = 0.001). The SCBG and SCG silages showed a higher B2 fraction (p < 0.0001) compared to the CS and SCS silages. The SCBG and SCP silages presented a higher C fraction (p = 0.001). For protein fractionation, the SCP and SCG silages showed higher crude protein contents (p = 0.001). The CS and SCS silages showed a higher A fraction (p = 0.001). The SCBG silage presented a higher B1 + B2 fraction (p = 0.001). The SCG silage showed a higher B3 fraction (p = 0.006) compared to SCBG silage. The SCS and SCP silages showed a higher C fraction (p = 0.001). Exclusive SCS silage showed higher in vitro dry matter digestibility (p = 0.001), dry matter degradability (p = 0.001) and total gas production (p = 0.001). The use of the SCBG, SCP and SCG silages to feed sheep increased the dry matter intake (p < 0.001). Sheep fed the SCG silage showed greater dry matter and crude protein digestibility compared to the sheep fed the CS, SCS and SCP silages (p = 0.002). There was a higher water intake (p < 0.001) with the use of the SCS and SCG silages to feed the sheep. The SCP and SCG silages provided a greater intake (p < 0.001) and excretion (p < 0.001) of nitrogen by the animals. Although there were no differences between the treatments for daily gains, lambs that received the spineless cactus-based silage associated with tropical forages showed higher gains (160–190 g/day) than lambs that received CS silage (130 g/day). Thus, the use of spineless cactus associated with buffelgrass, pornunça and gliricidia to prepare mixed silages (60:40) to feed sheep has potential use to feed sheep, with positive effects on nutrient degradation and increases in dry matter intake. Under experimental conditions, we recommend the exclusive use of spineless cactus silage associated with buffel grass, pornunça and gliricidia in feeding sheep in semi-arid regions, as it provides nutrients, water and greater daily gains compared to corn silage. [ABSTRACT FROM AUTHOR]

• Spineless cactus silage provide benefit inherent to the maintenance of water content. • The use of spineless cactus silage must be associated with a source of fiber. • Performance of sheep fed spineless cactus silage associated with tropical forages was investigated. • Roughage based on spineless cactus allowed gains above 200 g/day. The study aimed to evaluate the intake, apparent digestibility, nitrogen balance and productive performance in lamb fed spineless cactus silage associated with forages adapted to the semiarid environment. Forty intact crossbred lambs, with an average body weight of 22.65 ± 1.01 kg, were distributed in a completely randomised design with five treatments (diets based on: spineless cactus silage (SCS), spineless cactus + buffelgrass silage (SCBS), spineless cactus + gliricidia silage (SCGS), spineless cactus + pornunça silage (SCPS) and corn silage (CS; witness) and eight animals per treatment. Intake, apparent nutrient digestibility, nitrogen balance, and performance of animals were evaluated. The SCGS diet showed higher intake of dry matter and organic matter (P <0.05). The SCGS and SCPS diets showed the highest crude protein intake (P = 0.005). Lower intake of ether extract was found in animals receiving diets containing SCS and SCBS (P = 0.001). SCBS and SCGS provided a higher intake of neutral detergent fiber (P = 0.015). SCS and SCGS diets displayed a higher intake of non-fiber carbohydrates (P = 0.003). SCGS diets displayed the highest total digestible nutrients intake (P = 0.001). SCPS diet showed lower digestibility of dry matter, organic matter, and crude protein (P <0.05). SCGS diet showed a lower digestibility coefficient for ether extract (P = 0.009). SCPS diet showed lower digestibility coefficients for neutral detergent fiber (P = 0.022). SCS and SCPS diets showed lower digestibility coefficients for non-fiber carbohydrates (P = 0.011). The CS promoted lower results for intake (P = 0.003), absorbed (P = 0.003) and balance (P = 0.012) for nitrogen. SCPS diet promoted higher excretion of nitrogen via faeces (P = 0.001) and less excretion of nitrogen via urine (P = 0.033). SCGS diet provided a higher final weight (P = 0.006). SCS and SCGS diets provided more significant body weight gain (P = 0.001). Combining spineless cactus with a roughage base allowed weight gains over 200 g/day, proving to be efficient in diets for feedlot lamb and gains similar or superior to corn-based diets. [ABSTRACT FROM AUTHOR]