Abstract
Background: The researches on low-protein-level diets (LPD) indicated that even the profiles of essential amino acids (EAA) follow the recommendation for the normal-protein-level diets (NPD), broilers fed low-protein diets failed to achieve comparable productive performance as those fed with normal diets. Therefore, it is imperative to reassess the optimum profile of EAAs in low-protein diets and establish a new ideal pattern for amino acid balance. Furthermore, finding novel sensitive biomarkers for assessing amino acid balance will greatly facilitate the development of amino acids nutrition and application technology. In this study, twelve dietary treatments (Con(+), Con(-), L&A(-), L&A(+), M&C(-), M&C(+), BCAA(-), BCAA(+), Thr(-), Thr(+), Trp(-) and Trp(+)) were established by combining different EAAs including Lysine and Arginine, methionine and Cysteine, branched-chain amino acid (BCAA), threonine and tryptophan in order to observe the growth and development of the broiler chickens fed with low-protein-level diets. Based on biochemical parameters and metabolomics analysis from animals subjected to different treatments, were conducted to identify biomarkers associated with optimal and suboptimal amino acid balances.
Results: The growth performance, carcass characteristic, hepatic enzyme activities, serum biochemical parameters, and breast muscle mRNA expression showed significant differences between male and female broilers under different dietary amino acid patterns. Male broilers exhibited higher sensitivity to the adjustment of amino acid patterns compared to female broilers. For the low-protein diet, it was indicated that the dietary concentrations of lysine, arginine, and tryptophan were needed to be increased while not for the methionine, cystine, and threonine concentrations. Further research is needed on each individual BCAA. For metabolomic analysis, Con(+) was selected as a normal diet (NP) while Con(-) represented a low-protein diet (LP). L&A(+) denoted a low-protein amino acid balanced diet (LPAB) and Thr(+) represented a low-protein amino acid imbalance diet (LPAI). Metabolites oxypurinol, pantothenic acid, and D-octopine in the birds were significantly influenced by the different dietary amino acid paterns.
Conclusion: Adjusting the profile of amino acids in low-protein diets is required to obtain normal growth performance of broiler chickens as fed with normal-protein-level diets. Oxypurinol, pantothenic acid, and D-octopine were identified as potential sensitive biomarkers for assessing amino acid balance.