Elevated branched-chain amino acid inclusions generate distinctly divergent growth performance responses in broiler chickens offered wheat- and/or sorghum-based, reduced-crude protein diets

Abstract

The objective of this study was to determine the effects of elevated branched-chain amino acid (BCAA) inclusions in 187.5 g/kg crude protein (CP) diets based on wheat, sorghum or a wheat-sorghum blend on performance parameters of broiler chickens from 7 to 28 days post-hatch. The first tier of BCAA inclusions relative to lysine were leucine 105, isoleucine 65 and valine 75. The second tier was an elevation of leucine to 150 individually and in the third tier leucine was maintained at 150 and isoleucine and valine were elevated to 75 and 85, respectively. A 3 × 3 factorial array of these dietary treatments were offered to a total of 324 male Ross 308 broiler chickens housed in six replicate cages per treatment with six birds per cage. The assessed performance parameters included growth performance, relative abdominal fat-pad weights, nutrient utilisation, apparent jejunal and ileal digestibility coefficients of starch, protein (N) and amino acids and free amino acid concentrations in systemic plasma. Treatment interactions were observed for weight gain (P < 0.001) and FCR (P < 0.014). Elevated BCAA inclusions in sorghum-based diets significantly increased weight gain by 9.26 % (1451 versus 1328 g/bird) and numerically improved FCR by 0.86 % (1.378 versus 1.390). In contrast, elevated BCAA inclusions in wheat-based diets significantly depressed both weight gain by 9.49 % (1288 versus 1423 g/bird) and FCR by 8.33 % (1.665 versus 1.537). Wheat-based diets (5.68 g/kg) generated significantly lighter relative abdominal fat-pad weights than either sorghum-based (13.48 g/kg) or blended diets (12.95 g/kg). Sorghum-based and blended diets supported superior energy utilisation and N retention in comparison to wheat-based diets. Similarly, sorghum-based and blended diets supported higher jejunal and ileal starch digestibility coefficients than wheat-based diets, but wheat supported significantly higher jejunal protein (N) digestibility by 10.5 % (0.726 versus 0.657). Treatment interactions were observed for ileal digestibility of 4 amino acids (arg, lys, val, gly), BCAA inclusions significantly influenced 3 amino acids (ile, leu, thr) and the feed grain significantly influenced 10 amino acids (his, ile, leu, met, phe, ala, asp, glu, pro, tyr). Elevating BCAA inclusions in wheat-sorghum blended diets significantly increased free plasma concentrations of leucine and influenced concentrations of isoleucine and valine. However, BCAA inclusions significantly decreased plasma concentrations of threonine, asparagine plus aspartic acid, cysteine, glycine, proline, and serine. Consideration is given to possible reasons for the remarkable weight gain treatment interaction following elevated BCAA inclusions to sorghum- or wheat-based diets.