Technical Abstract: A commercial yeast culture feed supplement (Celmanax® SCP, Vi-COR, Mason City, IA, YC)was provided to turkeys throughout a 16 wk grow-out to determine if it would prevent the effects of stress on production and pathogen colonization. YC was provided either continuously at 100g/tonne (YC-CS) or intermittently during times of stress at 200 g/tonne (YC-IS). Birds were stressed with an environmental challenge of Escherichia coli and by transporting them in a vehicle for 3 hours after which they were penned in new social groups, without feed or water, for an additional 9 h. Turkeys were transported and challenged at 6, 12, and 16 wk of age to model the movement of birds within a 3-stage housing system. The YC-IS was provided only for the first wk after hatch and for a one wk period encompassing each challenge. At wk 7 and 9, a decrease in BW of challenged birds was prevented by YC-IS but not YC-CS. There were no significant differences in BW due to either challenge or YC during wk 11 and 13. At wk 16, challenge decreased BW but there was no difference in either of the YC treatments. Overall FCR was increased by transport/E.coli (P<0.0001). YC-CS improved FCR of challenged birds by 21 points while YC-IS improved FCR by 36 points and this effect was significant (P= 0.013). YC-CS tended to decrease both Salmonella and Campylobacter isolation from the ceca of stressed birds (P >0.05). YC-IS also tended to decrease Salmonella isolation (P.0.05) with no effect on Campylobacter isolation. These data suggest that the practice of transporting turkeys decreases performance and that YC-IS may be more effective than YC-CS for alleviating the effects of this stressor on feed efficiency.