Probioticsbeneficiallyaffectthehostanimalbyimproving its intestinal microbial balance. These bacteria are defined as live microorganisms that are host originated, nonpathogenic, resistant to gastric acid and bile. They have a high affinity for attachment to the mucosal wall, produce inhibitory compounds, and adjust to immune responses (Patterson and Burkholder, 2003). They produce beneficial changes in gut flora by manufacturing acids that inhibit the growth of harmful bacteria (Sun, 2005). Studies on the beneficial impact on poultry performancehaveindicatedthatprobioticsupplementationcan have positive effects. Kabir et al. (2004), for example, conducted a 6-wk growth performance study with broilers and found that live weight gain and carcass yields weresignificantly higherinbroilersfed probioticsupplementation.Theyalsofoundsignificantdifferencesamong spleen and bursa weights. Davis and Anderson (2002) reported that PrimaLac as a direct-fed microbiotic improved egg size and lowered feed cost in laying hens. Lan et al. (2003) found higher (P < 0.01) weight gains in broilers subjected to 2 probiotic species. However, Kara-oglu and Durdag (2005) used Saccharomyces cerevisiae as a dietary probiotic to assess performance and found no overall weight gain difference.