Working on laying hens, Dizaji and Pirmohammadi (2009) determined the effect of dietary probiotic containing Saccharomyces cerevisiae on body weight, daily feed consumption, egg production, egg weight, egg mass and feed conversion. In 10 weeks experimental period, hens (46 to 55 weeks of age) were allocated to four dietary treatments (0, 200, 300, 400g Saccharomyces cerevisiae/ton of diet). Using yeast caused significant improve in feed conversion and significant decrease in egg weight, however, it had no significant effect on the other parameters.