Intake, digestibility, nitrogen balance and energy utilization in heifers fed low-quality forage and Leucaena leucocephala

The aim of this study was to assess the effect of the inclusion of Leucaena leucocephala on dry matter (DM) intake and digestibility, nitrogen (N) balance and energy utilization in cattle fed a basal ration of Pennisetum purpureum and housed in metabolic crates. Five crossbred (Bos taurus × Bos indicus) heifers (BW: 295 ± 6 kg) were fed chopped P. purpureum grass and five increasing levels of L. leucocephala (0, 20, 40, 60 and 80% of DM) in a 5 × 5 Latin square design. The intake of DM was similar (P > 0.05) among treatments, with an average of 7.03 kg of DM/day. While the crude protein intake (CPI) linearly increased (P < 0.001) with the inclusion of L. leucocephala, the DM digestibility (average 492.3 g/kg DM) and OM digestibility (average 501.6 g/kg OM) were not affected (P > 0.05) by the incorporation of L. leucocephala into the ration. The N intake and excretion in the urine increased linearly (P = 0.0001, 0.0001) as the level of L. leucocephala in the ration increased. In addition, methane energy loss as a percentage of that in the control ration, was of only 61% (P = 0.0005) with 80% incorporation of L. leucocephala in the ration. We concluded that the inclusion of L. leucocephala has the capacity to reduce energy losses in the form of methane emissions. Nevertheless, the energy losses in the urine increased with the addition of L. leucocephala to the ration, with the optimal levels of incorporation in the ration fluctuating between 20 and 40% of the ration DM, which had no effects on the dry matter intake (DMI), organic matter intake (OMI) or the digestibility of dry matter (DMD).