The present study investigated the doseeffect relationship of graded levels of lipoic acid supplementation on growth performance and small intestinal development in a weaned rat model. Seventy-two weaned Sprague-Dawley rats, were fed semipurified diets （ n = 12 ）, either unsupplemented （ group I） or supplemented with 12.5,25,125, or 250 mg/kg body weight （ BW ） lipoic acid （ groups HI, IV, V, and VI）, with 200 mg/kg BW aureomycin as the antibiot- ic control （ group II）. The experiment lasted 21 days. Growth performance was not significantly different （P 〉 0.05） between rats under the antibiotic control （group I） and rats fed low levels （12. 5 and 25 mg/kg BW） of lipoic acid （groups III and IV）. In contrast,high level （125 and 250 mg/kg BW） lipoic acid supplementation （groups V and VI） （P 〈 0.05 ） reduced weight gain, feed consumption, and feed efficiency. In addition, high levels （125 and 250 mg/kg BW） of lipoic acid significantly （P 〈 0.05） reduced the villus height/crypt depth ratio, as well as the numbers of lactobacillus, total aerobes, and total anerobes in the gastrointestinal tract compared with the other treatments, which meant that high levels of lipoic acid impaired intestinal morphology and disordered the balance of intestinal microbiology. Furthermore,the results showed that high levels of lipoic acid supplementation （ P 〈 0.05 ） elevated interferon- γ and interleukin-2, but dramatically （ P 〈 0.05 ） depressed interleukin-4 and interleukin-10 compared with the low levels of lipoic acid supplementation and the control group, which indicated that high levels of lipoic acid would induce bias of Th1/Th2 lymphocytes. Taken together, the results indicate that lipoic acid supplementation can＇ t improve growth performance and intestinal development of normal animals, especially,high levels （ ≥ 125 mg/kg BW） of lipoic acid supplementation restrained growth performance and intestinal development, in association with unbalance of
