Performance, diameter of muscle fibers, and gene expression of mechanistic target of rapamycin in pectoralis major muscle of broilers supplemented with leucine and valine

Abstract

Two experiments were performed to study the interaction between the standardized ileal digestible (SID) leucine (Leu) and valine (Val) levels on the mRNA expression of genes involved in the mechanistic target of rapamycin (mTOR) pathway (experiment I) and determine the requirement of these amino acids in low-protein diets, and their effects on performance, serum parameters and muscle fiber diameters of broilers (experiment II) from day 1 to day 21 post hatch. Broiler chickens were distributed in a completely randomized design in a 3 × 3 and 5 × 5 factorial arrangement for a total of 9 and 25 treatments in experiments I and II, respectively. There was no (P > 0.05) interaction between the SID Leu and Val levels on mRNA expression of mTOR, S6 kinase 1 (S6K1), 4E-binding protein-1 (4EBP1), eukaryotic elongation factor 2 (eEF2), and insulin-like growth factor-1 (IGF-1) genes in pectoralis major muscle. Leucine supplementation increased (P < 0.05) mRNA expression of mTOR and S6K1 genes in muscle tissue, whereas Val supplementation did not affect (P > 0.05) mRNA expression of the genes investigated. Interaction was observed (P < 0.05) between dietary Leu and Val levels on feed intake and gain:feed. Leucine supplementation may stimulate mRNA expression of mTOR and S6K1 genes in pectoralis major muscle of broilers from day 1 to day 21 post hatch. The SID Leu and Val levels required for the optimization of feed intake, weight gain, and gain:feed in low-crude protein diets for broiler chickens from day 1 to 21 post hatch were estimated at 1.29% and 0.96%, 1.28% and 0.92%, and 1.27% and 0.91%, respectively; however, these requirements may be greater to maximize muscle fiber growth.

High leucine levels affecting valine and isoleucine recommendations in low-protein diets for broiler chickens

“…Some studies pointed out that feed intake reduction is the main cause of lower growth performance of broilers and pigs fed high Leu levels or BCAA imbalance diets ( Ueda et al., 1981 ; Farran et al., 2002 ; Wiltafsky et al., 2010 ; Wessels et al., 2016 ). High Leu levels mostly affected the feed intake in previous studies performed in our laboratory where SID Leu levels ranged from 1.0 to 1.96% from 1 to 21 D ( Ospina-Rojas et al., 2019 ), and 1.0 to 1.80% from 22 to 42 D ( Ospina-Rojas et al., 2017 ). In experiments 1, 2, and 3, feed intake was not affected by dietary Leu levels that ranged from 1.10 to 1.70%; 1.0 to 1.60%; and 0.98 to 1.58% during the starter, grower, and finisher periods, respectively.…”

“…In addition, Val and Ile supplementation could restore plasma concentration of these amino acids already oxidized by BCKD complex activation as a result of high Leu and KIC concentrations. Broilers fed high dietary protein content with amino acid levels greater than their minimum requirement did not exhibit reduced performance by high Leu levels ( Burnham et al., 1992 ; Waldroup et al., 2002 ), whereas the Leu antagonism has been more evident in low-protein diets where some amino acids could be at minimal dietary levels ( D'Mello and Lewis, 1970 ; Allan and Baker, 1972 ; Smith and Austic, 1978 ; Ospina-Rojas et al., 2017 , 2019 ). Then, the reduction magnitude of dietary protein may influence the bird response to SID Leu levels.…”

“…High dietary Leu has been demonstrated to activate the mTOR signaling pathways in pigs and broilers ( Suryawan et al., 2008 ; Torrazza et al., 2010 ; Deng et al., 2014 ; Chang et al., 2015 ). However, growth performance was not improved in a previous study with broilers fed high-Leu diets and graded Val levels, even though Leu supplementation increased the expression of genes involved in the mTOR signaling pathway of the pectoralis major muscle ( Ospina-Rojas et al., 2019 ). The reduced blood availability of other amino acids than Val could have limited the protein synthesis.…”

“…Dietary BCAA imbalance may affect broiler performance ( D'Mello and Lewis, 1970 ; Allan and Baker, 1972 ; Smith and Austic, 1978 ; Ospina-Rojas et al., 2017 , 2019 ), but other studies have indicated that excess Leu does not compromise broiler performance when protein levels are higher than broiler requirement ( Burnham et al., 1992 ; Waldroup et al., 2002 ). Then, the ideal BCAA ratio in low-protein diets should be different from high-protein diets and should be studied.…”

“…Then, the ideal BCAA ratio in low-protein diets should be different from high-protein diets and should be studied. In previous studies, we estimated the ideal Val/Leu ratio in starter and grower diets ( Ospina-Rojas et al., 2017 , 2019 ), but we did not consider the effect of Ile levels to estimate the optimal BCAA ratio in low-protein diets. Several reports have estimated the Leu, Val, and Ile requirements separately without considering the interactions between them.…”