A Microbiologist’s View on Improving Nutrient Utilization in Ruminants

The rumen is an open fermentation chamber, inhabited by microorganisms that anaerobically digest complex components of feedstuffs and generate fermentation products (mainly acids) and microbial cell mass for utilization by the host. The absorption of fermentation products, mainly VFA, from the rumen into the blood, and outflow of microbial cells to the abomasum and small intestine provide the animal energy and protein, respectively. The microbial ecosystem of the rumen is probably the most extensively described gut microbial ecosystem because of the importance of ruminants as a source of meat and milk. The rumen environment, created by interactions between the animal and the microbes, operates as an efficient continuous culture system with optimal physical and chemical conditions for microbial growth and activities, more or less continuous availability of substrate (at least in grazing cattle), removal of end products (by absorption, eructation or passage), and passage of undigested feed (Figure 1).