Abstract: 【Objective】An experiment was conducted to investigate the effect of dietary phytosterol level on growth performance, hematology, plasma biochemical traits, weight or length indices of organs, and histopathological changes of Arbor Acres broilers during periods of days 1-21 and 22-42 to evaluate the biological safety of phytosterols for broilers chicks. 【Method】A total of 240 1-d-old broilers (half male and half female) were randomly allocated by bodyweight to one of four treatments with six replicate cages of ten broilers (half male and half female) per cage. Birds were fed the phytosterol-unsupplemented diet with background about 300 mg•kg-1 of total phytosterol or the basal diet supplemented with 80, 400, or 800 mg•kg-1 phytosterols for an experimental duration of 42 days, and which was divided into two periods: start period from day 1 to 21 and growth period from day 22 to 42. Data from the experiment were analyzed by the general liner model procedure of SAS 9.0. 【Result】 Results showed that body weight gain, feed intake, feed conversion and mortality from the starter period and weight gain, feed conversion and mortality from growth period were not affected (P＞0.05) by the addition of phytosterols in diets, but birds fed the diet supplemented with 400 mg•kg-1 phytosterols had lower (P＜0.05) feed intake during growth period compared with the control group or the group supplemented with 80 mg•kg-1 phytosterols; most of biochemistry parameters in chicks from start period and all of biochemistry parameters from growth period were not affected by the addition of phytosterols in diets in the growth period, but which affected the concentration of total protein, album, and creatine, and alanine transaminase activity in plasma on day 21, and the total protein and album concentrations and alanine transaminase activity in plasma on day 21 increased (P＜0.05) when birds were fed the diet supplemented with 800 mg•kg-1 phytosterol. The addition of 400 mg•kg-1 phytosterol reduced (P＜0.05) the plasma creatine concentration on day 21. The relative weight of organ was not affected (P＞0.05) by the addition of phytosterols in diets except for pancreas, and the relative weight of pancreas on day 42 was significantly (P＜0.05) increased by the addition of 80 or 400 mg•kg-1 phytosterols. There were no significant differences (P＞0.05) in blood physiological among all treatment groups in the experimental period. No pathological changes in heart, liver, lung, kidney, and pancreas were observed among all phytosterol treatment groups at the end of the experiment. 【Conclusion】 Phytosterols added in diets at 80 to 800 mg•kg-1 have no significant effect on growth performance, hematology, plasma biochemical traits, and the development of organs, and there are no toxic response in broilers. So when corn-soybean meal basal diet containing 300 mg•kg-1 of phytosterols, the upper limitation of added phytosterols at 80 mg•kg-1 (containing about 400 mg•kg-1 total phytosterols ) in the corn-soybean meal diet would be safe for broilers.

Key words: phytosterols , biological safety , broilers