In situ rumen hydrogen concentrations in steers fed eight times daily, measured using a mercury reduction detector

Abstract

Dissolved hydrogen was measured in the bovine rumen using an in situ hydrogen probe coupled to a mercury reduction detector. The probe can quantitate dissolved hydrogen from low nM con- centrations to saturation. In the rumen of steers fed every 3 h, basal hydrogen concentrations aver- aged 1.38 #M :t: 0.26, and the basal level remained stable throughout an 18-25 h period. In contrast, a steer fed once a day had a basal hydrogen concentration of 1.40/~M, but the level was not stable between feedings. For the steers fed every 3 h, the reticulum displayed the most dramatic fluctuations in the hydrogen concentration after the feeding event. Hydrogen spikes (10-20 #M) in the reticulum were detected 2 rain after feed inges- tion, and lasted for 30 rain. In the center of the rumen the feeding response was observed 30 min after feeding and typically lasted 1 h. The magni- tude of hydrogen spikes in the center of the rumen was reduced in comparison to the reticulum. The magnitude of the hydrogen spikes indicates that feeding steers as frequently as eight times a day does not establish a steady-state with respect to hydrogen concentration. However, frequent feed- ings do minimize drift from the basal hydrogen level. Assuming Michaelis-Menten kinetics our data predict that methane production from hydro- gen proceeds at 22% of its maximal velocity.