Nitrogen balance of bullocks fed Cratylia argentea and Brachiaria arrecta Hay

Resumen

Four experimental diets or treatments formed with incremental proportions of the foliage of tropical shrub legume Cratylia argentea and decremental proportions of Tanner grass (Brachiaria arrecta) hay: T1, 0:100; T2, 15:85; T3, 30:70; and T4, 45:55 were evaluated using four Holstein-Zebu bullocks (214.5 9.3 kg) conned in individual pens, under a balanced 4 x 4 latin square design. The crude protein (CP, %) content of C. argentea was 19.3 ± 6%, and in the grass was 6.2 ± 3%. The intake of DM increased as the C. argentea level in the diet increased. Blood urea-N (BUN) showed a linear increase from T1 to T4, observing its highest concentration at feeding time and six-hours after in T4: 12.00 and 14.75 mg dL^-1, respectively. Purine derivatives (uric acid and allantoin) were not affected by treatments (p > 0.05). The increase of the legume in the diet improved the DM intake and digestibility, and led to N-balance from negative in T1 and T2, to positive in T3 and T4. The legume proportion in a basal diet of the grass B. arrecta must be 30% at least.