Research note: effect of increasing dietary concentrate levels on microbial biotin metabolism in the artificial rumen simulation system (RUSITEC).

The effect of varying hay/barley-proportions in the feed ration on biotin metabolism of rumen microbes was studied by means of the rumen simulation technique RUSITEC. The stepwise replacement of hay by barley decreased dietary biotin and the net output of biotin by the microbial metabolism. It is concluded that rumen microbes utilise more and/or synthesize less biotin with increasing proportions of dietary barley. These results indicate that a critical reconsideration of current views with regard to the supply and requirement of the high yielding dairy cow for biotin is necessary.