Composition of ruminal bacteria harvested from steers as influenced by dietary energy level, feeding frequency, and isolation techniques.

The effects of isolation techniques and time of sampling on composition of ruminal bacteria were examined in four steers fed two energy levels (2.24 or 2.92 Mcal metabolizable energy/kg DM) at two feeding frequencies. Diets were alfalfa hay and corn silage or ground corn/corn silage and were fed twice or 12 times daily. Whole ruminal contents were collected at four time intervals over a 4-d period. Fluid- and particle-associated bacteria were isolated. Energy level, feeding frequency, and preisolation freezing had little effect on composition of bacteria. Sampling time did not affect composition of bacteria harvested from steers fed frequently but had linear and quadratic effects on concentrations of cell components of bacteria harvested from steers fed twice daily. Differences were observed in the composition of bacteria harvested from the fluid phase compared with particle-associated or mixed populations of ruminal bacteria. These differences translated into different estimates of bacterial N supplied to the small intestine depending on N:purine ratio used. Composition of bacteria may be affected by fraction of contents sample and by time of sampling for animals fed infrequently. Freezing of samples before isolation of mixed bacteria does not appear to affect composition or estimates of bacterial N flows to the small intestine.