Abstract: An apparatus and corresponding method obtains time-integrated samples of fluid from the rumens of cattle, sheep, goats or other animals through a cannula. The apparatus allows ruminal fluid to be sampled under standard conditions. It reduces the labor required to obtain samples and allows dynamic fermentation patterns to be followed. The apparatus includes a ceramic filter connected to a sampling tube assembly. The filter is placed in the rumen and vented to atmosphere by a first tube. A second tube connects an inside region of the filter to a peristaltic pump which removes fluid for time-integrated sampling.