Continuous in vitro rumen systems.

I n vitro rumen experiments have been conducted for at least 40 years, and many research problems have been examined successfully by this approach. The simplest sub-division of in vitro rumen systems is into batchand continuous-culture types. The batch-culture approach involves the provision of an initial supply only of substrate, which results in a culture in which the concentration of substrates is constantly falling while that of waste products rises. The continuous-culture type of in vitro rumen aims to replenish the substrates and remove waste products over an extended culture period. This is, of course, the situation in vivo and most in vitro systems have employed an intermittent addition of fresh substrate in order to simulate natural conditions as closely as possible. Before evaluating these and other systems it is profitable to consider the nature of the natural rumen as a microbial environment.