Since the gut environment is generally assumed to be anaerobic, studies of the monogastric intestinal microflora have concentrated on the anaerobic microorganisms. However, the intestinal epithelium constitutes a very high surface area in relation to the volume of the gut contents, and all of this surface area is richly supplied with blood. Appreciable dissolved oxygen concentrations can be detected in the intestines of anaesthetised piglets (Hillman et al, 1993), although this is never detectable in the intestines of killed animals. It was considered important to investigate the persistence of intestinal oxygen after death, in order to determine the accuracy of postmortem measurements of this component of the intestinal environment. This report demonstrates the rapidity of removal of oxygen by porcine colon contents, and indicates that, since the oxygen supply to the intestine stops when the blood circulation stops, accurate measurements of dissolved oxygen can never be made in the intestines of killed animals.

Colon contents were obtained from three freshly slaughtered 20 kg piglets and diluted to 20% (w/v) slurries in quarter-strength Ringer's solution (Unipath, UK). The slurries were transferred (25 ml) to 50 ml conical flasks, stirred by magnetic follower (approx 400 rpm) and surrounded by a water jacket to maintain a temperature of 39°C in the vessel contents. A polarographic oxygen electrode was inserted so that the membrane was submerged. Gas flow through the headspace was provided by compressed air and nitrogen, mixed via a pair of needle valves to provide a constant flow rate of 600 ml min-1. Calibration of the system was performed in sterile Ringer's solution using air and oxygen-free nitrogen: calibration was repeated between each experiment.