Effects Of BCAAs On Small Intestinal Development And Relative Genes Expression Of TOR Pathway In Broilers

This study was conducted to investigate the effects of branched-chain amino acids(BCAAs) or leucine levels on small intestinal development and relative genes expression of TOR pathway in broilers, and try to explore the function mechanism of BCAAs on broilers’ small intestinal development.Experiment 1: Effects of branched-chain amino acids levels on small intestinal development and relative genes expression of TOR pathway in broilers. Three hundred and eighty-four one-day-old broilers were randomly assigned into four treatments, 6 replicates in each treatment and 16 broilers in each replicate. Each treatment was offered one of the following diets with different BCAAs levels: 3.04%(3.04TM), 3.93%(3.93TM), 4.82%(4.82TM) and 5.71%(5.71TM), respectively. The ratio of Leu to Ile and to Val was 1.8:1:1.2. The experiment lasted for 21 days and all birds were free to feed and water. The results indicated that: there was no significant difference in body weight or average daily gain among all treatments(P>0.05), while the average daily feed intake in 5.71 TM was significantly lower than that in 3.04TM(P<0.05), the ratio of feed to gain in 4.82 TM and 5.71 TM was significantly lower than that in 3.04TM(P<0.05). The weight of unit length of duodenum, as well as the relative weight of jejunum rose with the increasing level of BCAAs from 3.04% to 4.82% on 14 and 21 day. Additionally the weight of unit length of duodenum and the relative weight of jejunum in 4.82 TM was significantly higher than that in 3.04TM(P<0.05). The weight of unit length of duodenum was significantly decreased as the level of BCAAs increased to 5.71%(P<0.05). The villus height of the small intestine increased with increasing level of BCAAs during the entire experimental period. Moreover, the villus height of duodenum and ileum in 4.82 TM was significantly higher than that in 3.04 TM on 14, 21 day(P<0.05), and the villus height of jejunum in 4.82 TM was significantly higher than that in 3.04 TM on 10, 14 day(P<0.05). However, the villus height of the small intestine was significantly decreased as the level of BCAAs increased to 5.71%(P<0.05), and was lower in comparison with 4.82% dietary BCAAs(P<0.05). On d 7, 14 and 21 of the trial, the expression of TOR, S6K1 and 4E-BP1 in the duodenum and jejunum increased with increasing leucine level form 3.04 to 4.82%, and TOR, S6K1 and 4E-BP1 expression of duodenum and jejunum in 4.82 TM was higher than that in 3.04 TM, which no significant difference found as compared with 5.71TM(P>0.05). In conclusion, increasing the level of BCAAs appropriately can improve the efficiency of feed utilization of broilers, while excessive supplementation(5.71%) can significantly decrease average daily feed intake. Villus height and relative genes expression of TOR pathway in the duodenum and jejunum increased with increasing leucine level form 3.04 to 4.82%, promoting the development of small intestinal villus. While villus height and V/C of small intestine decreased significantly, as well as relative genes expression of TOR pathway in the duodenum and jejunum down-regulated with leucine level increased up to 5.71%, leading to the postponed development of small intestinal villus.Experiment 2: Effects of leucine levels on small intestinal development and relative genes expression of TOR pathway in 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 treatments were offered the following diets with 1.37, 1.77, 2.17 and 2.57% of leucine. These diet treatments were named 1.37 TM, 1.77 TM, 2.17 TM, and 2.57 TM. 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 relative weight of duodenum, jejunum and ileum decreased when leucine addition up to 2.57%. The broiler duodenal villus height in 2.57 TM was the lowest, while the highest occurred in 1.37 TM on d 7, 10 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 2.17 TM than in 1.37 TM on d 7, 10 and 14, and the ratio of V/C in the ileum increased with the increasing level of leucine on d 10, 14 and 21, while V:C ratio of ileum in 2.17 TM higher than that in 1.37 TM and 1.77TM(P<0.05). The V/C ratio in the duodenum, jejunum and ileum increased significantly on d 21. The gene expression level of TOR in the duodenum decreased with increasing leucine level and was higher in 1.37 TM than in 2.57 TM 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 1.37 TM than in 2.57TM(P<0.05), and the expression of TOR, S6K1 in the jejunum and ileum increased with increasing leucine level form 1.37 to 2.17%, whereas a significant difference occurred between 1.37 TM and 2.17TM(P<0.05). In conclusion, the growth performance of broilers has no response to the addition of leucine. However, small intestinal villus development was improved by enhancing villus height and the genes expression of TOR, S6K1 in the jejunum and ileum as the level of dietary leucine elevated from 1.37 to 2.17%. Villus hight and relative genes expression of TOR pathway were down-regulated rather than up-regulated when leucine added up to 2.57%, adversing to the development of small intestinal villus.In conclusion, increasing the level of BCAAs appropriately in broilers ration could improve the feed conversion ratio, increase relative genes expression of TOR pathway and villus hight in the duodenum and jejunum, promoting the development of small intestinal villus. However, the average daily feed intake, relative genes expression of TOR pathway and villus height in the duodenum and jejunum were decreased if its supplement level too high(5.71%), depressing the development of small intestinal villus. On the other side, by keeping the same level of Ile and Val in the ration, increasing the level of Leu appropriately could make TOR and S6K1 genes expression up-regulated and the villus height increased in the jejunum and ileum, facilitating the development of small intestinal villus. Whereas high level of Leu added(5.71%) in the ration, relative genes expression of TOR pathway were down-regulated rather than up-regulated, thus retard the development of small intestinal villus.