Use of a semi-continuous culture system (RUSITEC) to study the effect of pH on microbial metabolism of thiamin (Vitamin B1).

Abstract

Polioencephalomalacia (P.E.M.) in ruminants is often associated with high concentrate diets and rumen acidosis; this syndrome is classically related to a disturbance of the rumen metabolism of thiamin. An in vitro model using a semicontinuous system (RUSITEC) was used to investigate the effect of pH on microbial metabolism and on production of thiamin in the rumen. These effects were tested using either a natural diet (hay/wheat) or a semi-synthetic one. Lowering the pH decreased total volatile fatty acids, methane and microbial nitrogen production. Molar proportions of VFA were modified by an increase in butyric, valeric and caproic acids. Microbial production of thiamin was comparable to in vivo synthesis but decreased when the diet was enriched with thiamin. The diet of the donors of inoculum had no effect on this metabolism. For all diets, lowering of pH did not reduce microbial production of thiamin. Thiaminase activity in the liquid phase of fermentors was very low and was not modified by pH. Thus lowering of pH in vitro, had no deleterious effect on microbial production of thiamin. Therefore, lowering of the rumen pH in acidotic conditions may not be a factor which promotes P.E.M.