The effect of energy and nitrogen (N) supply pattern on rumen bacterial growth was investigated in vitro. In experiment 1, glucose was was fed to batch cultures of mixed rumen bacteria according to three patterns namely a pulse dose at time zero (P); even increments at 0.5-h intervals (G) or an intermediate pattern (I), whilst N was supplied in excess. In experiment 2, glucose and N (not in excess) were fed to batch cultures according to four patterns namely glucose and N as pulse doses at time zero, (EPNP); glucose as a pulse dose at time zero and N in 24 even increments at 0.5-h intervals (EPNG); glucose in 24 even increments at 0.5-h intervals and N as a pulse dose at time zero (EGNP) or both glucose and N in 24 even increments at 0.5-h intervals (EGNG). Fermentaton was studied over a 12-h period for both experiments. In experiment 1, bacterial growth efficiency and specific growth rate (39.8, 35.5 and 29.9 (g bacterial dry matter (DM) per mol glucose utilized) and 0.33, 0.27 and 0.20 (fraction per h) for treatments P, I, and G respectively) differed significantly between glucose supply patterns. In experiment 2, bacterial growth efficiency and specific growth rate (33.8, 34.7, 25.9 and 22.5 (g bacterial DM per mol glucose) and 0.21, 0.18, 0.14 and 0.13 (fraction per h) for treatments EPNP, EPNG, EGNP and EGNG respectively) differed significantly only between glucose supply patterns. It is concluded that the pattern according to which a given amount of energy becomes available affects bacterial growth efficiency, with the fastest supply rate giving the highest efficiency and that, within accepted levels of N supply, synchronization between energy and N availability may be of less importance to bacterial growth efficiency than the energy supply pattern.
