Effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin signaling pathway and intestinal development of broilers

This experiment was to investigate the effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin (mTOR) signaling pathway and intestinal development of broilers. A total of 384 one-day-old broilers were randomly assigned into 4 treatments with 6 replicates (16 broilers per replicate). Broilers in these treatment groups were offered the following diets with 1.37, 1.77, 2.17 and 2.57% of leucine. These diet treatments were named 1.37TM, 1.77TM, 2.17TM, and 2.57TM. The experiment lasted 21 days and all birds had free access to feed and water. Results indicated that there was no significant difference in body weight, average daily gain and average feed intake among all treatments (P > 0.05). The broiler duodenal villus height in 2.57TM was the lowest, but the highest occurred in 1.37TM on d 7 and 14 (P < 0.05). The villus height in the jejunum and ileum increased along with leucine level from 1.37 to 2.17%. The villus height of jejunum was significantly higher in 2.17TM than in 1.37TM on d 7 and 14, and the ratio of villus height to crypt depth (V:C) in the duodenum, jejunum and ileum increased significantly (P < 0.05) on d 21. The gene expression level of mTOR in the duodenum decreased with increasing leucine level and was higher in 1.37TM than in 2.57TM on d 7 and 14 (P < 0.05). On d 14 and 21 of the trial, the expression of S6K1 in the duodenum was higher in 1.37TM than in 2.57TM (P < 0.05), and the expression of mTOR, S6K1 in the jejunum and ileum increased with increasing leucine level form 1.37 to 2.17%, whereas a significant difference occurred between 1.37TM and 2.17TM (P < 0.05). In conclusion, the addition of leucine fails to enhance the growth performance of broilers. However, leucine can improve intestinal development by enhancing villus height and V:C ratio in the jejunum and ileum. Moreover, the expression of mTOR, S6K1 increased as the level of dietary leucine was elevated from 1.37 to 2.17%.