Abstract
The objective of this study was to investigate the impacts of dietary crude protein (CP), fishmeal and sorghum on nutrient utilisation, digestibility coefficients and disappearance rates of starch and protein, amino acid concentrations in systemic plasma and their relevance to growth performance of broiler chickens using the Box-Behnken response surface design. The design consisted of three factors at three levels including dietary CP (190, 210, 230 g/kg), fishmeal (0, 50, 100 g/kg), and sorghum (0, 150, 300 g/kg). A total of 390 male, off-sex Ross 308 chicks were offered experimental diets from 14 to 35 days post-hatch. Growth performance, nutrient utilisation, starch and protein digestibilities and plasma free amino acids were determined. Dietary CP had a negative linear impact on weight gain where the transition from 230 to 190 g/kg CP increased weight gain by 9.43% (1835 versus 2008 g/bird, P = 0.006). Moreover, dietary CP linearly depressed feed intake (r = -0.486. P < 0.001). Fishmeal inclusions had negative linear impacts on weight gain (r = -0.751, P < 0.001) and feed intake (r = -0.495, P < 0.001). There was an interaction between dietary CP and fishmeal for FCR. However, growth performance was not influenced by dietary inclusions of sorghum. Total plasma amino acid concentrations were negatively related to weight gain (r = -0.519, P < 0.0001). The dietary transition from 0 to 100 g/kg fishmeal increased total amino acid concentrations in systemic plasma by 35% (771 versus 1037 μg/mL, P < 0.001). It may be deduced that optimal weight gain (2157 g/bird), optimal feed intake (3330 g/bird) and minimal FCR (1.544) were found in birds offered 190 g/kg CP diets without fishmeal inclusion, irrespective of sorghum inclusions. Both fishmeal and sorghum inclusions did not alter protein and starch digestion rate in broiler chickens; however, moderate reductions in dietary CP could advantage broiler growth performance.
Highlights
Developing reduced crude protein (CP) diets where soybean meal partially replaced with supplementary amino acids is a promising nutritional strategy to achieve sustainable chicken meat production with reduced nitrogen excretion and improved bird welfare
Starch and protein digestive dynamics in broiler chickens are important for optimising growth performance in broiler chickens offered reduced-CP diets because dietary CP reduction increases non-bound amino acid (NBAA) inclusions and starch content [3]
The overall average weight gain and feed intake for all treatments from 14 to 35 days post-hatch were higher than 2019 Ross performance objectives by 3.41% (1912 versus 1849 g/bird) and 4.48% (3052 versus 2921 g/bird), respectively and FCR was comparable (1.601 versus 1.579)
Summary
Developing reduced crude protein (CP) diets where soybean meal partially replaced with supplementary amino acids is a promising nutritional strategy to achieve sustainable chicken meat production with reduced nitrogen excretion and improved bird welfare. Starch and protein digestive dynamics in broiler chickens are important for optimising growth performance in broiler chickens offered reduced-CP diets because dietary CP reduction increases non-bound amino acid (NBAA) inclusions and starch content [3]. Both glucose and monomeric amino acids are co-absorbed with Na+ via their respective Na+-dependent transport systems; whereas, di- and tri- peptides are absorbed via PepT-1 transporter [4, 5]. The objective of the present study was to evaluate the relevance of starch and protein digestive dynamics in reduced CP diets by varying inclusion levels of fishmeal and sorghum in a wheatsoybean-meal based diets
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