Fate of Levucell SC I-1077 yeast additive during digestive transit in lambs.

The fate of a live yeast strain, which was used as a feed additive for ruminants (Levucell SC I-1077), was studied during digestive transit in two gnotoxenic lambs reared in a sterile isolator. The number of live yeast cells were counted in the rumen and in faeces after a single administration or a daily feeding of 100 mg of Levucell SC. If the supplement was not renewed, the live yeast cells persisted in the rumen for approximately 30 h at a level close to the initial value. They were then gradually cleared. They began to be excreted with the faeces approximately 8 h after their consumption and were no longer detected after 102 h. Yeast additives did not colonize the rumen. As 17 to 34% of yeast cells remained alive during their transit through the digestive tract, their effect might extend beyond the rumen the post-ruminal compartments.