Live yeast Saccharomyces cerevisiae NCYC Sc 47 was added to the diet of weaning rabbits (35d old) to analyse the effects on the caeca! ecosystem (biotope and bacterial community), digestion and health status. Two levels of yeast (1 and 10 g/kg feed, group C1 and C10 corresponding to 10(6) and 10(7) CFU/g DM) were compared to a control group (C0) without live yeast addition. Three groups of 10 young rabbits were used in a first experiment to measure digestibility and caecal parameters and to calculate the yeast survival rate in the digestive tract. Growth performance and health status were studied on 3 further groups of 40 rabbits (Experiment 2). The live yeast concentration fell slightly after diet pelleting (0.1-0.5 log CFU/g DM), at 70-80 degrees C. The survival rate of yeast in digestive tract was high and increased from 90 to 97% (P<0.01) with increasing yeast supplementation. Live yeast addition did not modify the total tract digestibility of nutrients, or the growth performance. Mortality rate between 42 and 56d of age was lower at the highest yeast level (C10: 4 dead on 40; P<0.05) compared to C0 and C1 groups (average 13/40),. The structure of the caecal bacterial community was not modified after 11d of yeast presence in the caecum, while the bacterial diversity tended to be higher (5.0 vs 5.4, P=0.10, for C0 vs [C1+C10]). The redox potential of the caecal content increased with yeast addition (-227 vs -251 my, P<0.05 for CO vs [C1+C10]), whereas the fermentation pattern and the caecal pH remain unaffected (meanly 5.88). (C) 2012 Elsevier B.V. All rights reserved.