[Rumen bacterial metabolism as affected by extracellular redox potential]

The redox potential (Eh) in the digestive tract of ruminants varies mostly within the ranges from -300 to +200 mV, in the rumen medium: from -130 to -200 mV. Eh and pH changes are of a linear character. Enhanced fermentation moves Eh towards negative values and improves growth of microorganisms. Eh values become even more negative as affected by Na2S, NaOH, cysteine and NaHSO3. Addition of picrate, sodium nitrate, hydrochloric acid, copper sulphate, gaseous oxygen and particularly heavy metals (silver and mercury) promotes positive Eh values and inhibits metabolism. Optimum Eh values for Megasphaera elsdenii are more negative, than those for Streptococcus bovis. In the process of S. bovis growth, the production of lactate, VFA, CH2O2 and NH3 increases, Eh and pH values decrease. More positive Eh values inhibit metabolism and growth rates of Selenomonas ruminantium, Bacteroides amylophilus, Bacteroides succinogenes and Streptococcus bovis to different degrees.