Abstract: One hundred and eighty seven-day-old Hy-line Brown laying chicks were chosen and divided into three groups randomly, three replicates per group, twenty chicks per repetition. The chicks in the controlled group were fed with basal diet. The chicks in experiment group Ⅰ and Ⅱ were fed with basal diets distinctively added with 2.5% and 5% yeast culture for six weeks. The experiment aimed to investigate systematically the effect of yeast culture on the growth performance, immune organs development and serum related hormones concentration of laying chicks. The results showed as follows:①Addition of yeast culture could elevate the average daily gain(P＜0.05),reduce the feed/gain(P＜0.05) and elevate the survival rate(P＞0.05) of laying chicks. ②Addition of yeast culture enhanced immune organs development and elevated their weigh index(P＜0.05). ③Yeast culture addition elevated serum T3 and T4 concentration(P＜0.05) and reduced serum COR concentration(P＜0.05). The concentration of GH in experiment group Ⅰand Ⅱ were higher than that of the control, but the difference was not significant(P＞0.05).

Key words: yeast culture; growth performance; immune organs; hormone