Increasing dietary leucine in Ross broilers affects gut permeability but not growth responses

We investigated dietary branched-chain amino acid responses in commercial broilers with a factorial design (2 × 2 × 7) containing a Leu titration. Ross 344 x Ross 308 male broilers (2,304) randomized across 192 floor pens were fed nutritionally adequate diets from d 1 through 14 and provided dietary treatments from d 15 to 35. Dietary treatments had 6 replications and consisted of varying digestible amino acids relative to Lys: 0.76 and 0.80 Val, 0.65 and 0.68 Ile, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, and 1.75 Leu, and a titration comparison positive control diet containing 1.35 Leu. Interactions (P < 0.05) were limited to Ile and Val and occurred for BW gain, feed intake, and carcass yield. Birds fed a Val to Lys 0.80 and Ile to Lys of 0.65 had improved BW gain and feed intake that birds fed a Val to Lys 0.76 and Ile to Lys of 0.65. However, improved carcass yield occurred in birds fed Val to Lys of 0.76 and Ile to Lys of 0.65 or Val to Lys 0.80 and Ile to Lys of 0.68 with birds fed Val to Lys 0.80 and Ile to Lys of 0.65 being intermediate. BW gain of birds fed 1.35 Leu to Lys in the titration or control diet did not differ (P = 0.19), and birds fed the titration diet with 1.35 Leu to Lys had higher (P < 0.05) feed intake and feed conversion than birds fed the control diet. Although linear or quadratic Leu to Lys live performance responses were not detected (P > 0.05), birds fed increasing Leu to Lys had worsened intestinal permeability (linear; P = 0.04). Birds fed the Leu to Lys titration diet of 1.35 had higher (P < 0.05) fat and breast yields than bird fed the control diet with equal Leu to Lys, which may be attributed to increased feed intake. Decreasing quadratic responses (P < 0.05) to increasing Leu to Lys occurred for both Pectoralis minor and leg quarter yields. Dietary Leu by Val and Ile interactions did not occur, indicating the ability of Ross 308 male broiler to be fed diets with relatively high Leu. However, as dietary Leu increased, broilers had compromised intestinal barrier integrity. Amino acid levels tested mimic industry relevance and necessitates the need for more branched-chain amino acid research involving intestinal health.