Efficiency of utilization of dietary nitrogen for milk production by dual-purpose cows fed increasing levels of Leucaena leucocephala forage mixed with Pennisetum purpureum grass

Efficiency of nitrogen utilization (g N in product/g N intake; ENU) by ruminants is low with an average of ~25% (Calsamiglia et al., 2010), but with an ample range of variation (15-40%) suggesting that improvements are possible. It is of paramount importance to increase the efficiency of N utilization in order to improve productive performance (i.e. milk yield) and reduce excretion of nitrogenous products in urine and feces from ruminants to the environment. Silvopastoral systems represent a viable means of increasing levels of animal production in the tropics. Usually, high CP legumes are employed in those systems and the possibility of N loss from the gastrointestinal tract (Poppi and McLennan, 1995) may constraint productive limits.