Effect of 'Stylosanthes guianensis' supplementation on intake and nitrogen metabolism of 'Bos indicus' cattle offered a basal diet of mixed rice straw and tropical grass

The effect of supplementing a mixed rice straw and tropical grass diet with legume as a nitrogen (N) source on intake, digestibility, rumen ammonia and microbial protein production was evaluated in 'Bos indicus' cattle. Four rumen-cannulated steers were used in a crossover design with two diets and two periods. The diets were T1 = 40% rice ('Oryza sativa L.') straw + 60% grass ('Brachiaria' spp. cv. Mulato II hybrid) and T2 = 40% rice straw + 30% grass + 30% legume ('Stylosanthes guianensis' cv. CIAT184) on DM basis. Supplementation with legume doubled (P<0.01) rice straw and total N intake, and increased total DM intake by 32%. It did not affect the DM, organic matter, neutral detergent fibre and acid detergent fibre digestibility (P>0.05) but did increase (P<0.05) N digestibility. Faecal N and total N outputs from T2 cattle were higher (P<0.05) than T1 cattle, but urinary N output did not differ between diets (P>0.05). N retention in T2 cattle was improved by 83% (P<0.05) compared with T1 cattle. Rumen ammonia concentration, microbial protein production and efficiency of microbial protein production were improved (P<0.05) when the legume forage was included in the straw–grass diet. We conclude that when a mixed rice straw and fresh grass diet is supplemented with ~30% legume (DM basis), significant improvements in DM and N intake can be achieved.