The nutritive value of rumen micro-organisms in ruminants. 2. The apparent digestibility and net utilization of...

Four experiments were conducted with eighteen lambs sustained entirely by intragastric nutrition at gross energy inputs varying from 430 to 860 kJ/kg live weight0.75 (W0.75). Isolated rumen micro-organisms (RMO) were infused into the abomasum in quantities varying from 0 to 2 g digestible N/kg W0.75 to assess the increase in N balance as a result of increasing RMO input when N was limiting. The over-all utilization of N from RMO (RMO-N) could be described by the equation y = 0.543 X -0.457, residual SD = 0.037, where y is the N balance and X is the abomasal input of RMO-N, both expressed in g/kg W0.75. Thus the coefficient of efficiency of utilization of infused RMO-N was 0.543 (SE 0.008). The coefficient of efficiency of utilization of RMO-N truly digested (i.e. the biological value) was 0.659 (SE 0.015). The RMO-N input (mean with SE) at N equilibrium was 0.843 (0.009) g/kg W0.75. The true digestibility of RMO-N was 0.813 (0.004). The urinary N excretion when no N was infused was 0.329 (0.008) g/kg W0.75 and the N excreted via the faeces with zero N input was 0.036 (0.009) g/kg W0.75.