The Effects of Reduced Protein Diets on Growth Performance and Amino Acid Utilisation in Broiler Chickens

Abstract

Protein requirements for broiler chickens can largely be met with the supplementation of non-bound amino acids (crystalline or synthetic), offering a more economical feasible alternative to soybean meal with the potential to reduce its inclusion by as much as 40%. However, current reduced-crude protein (CP) diets present do have drawbacks which have impacted its acceptance within the poultry industry. A key drawback is the limitation to which protein bound amino acids can be reduced and replaced with non-bound amino acids before it compromises bird performance, including weight gain, feed conversion ratios and carcass quality. For reduced-CP diets, feed grain is most pertinent to bird performance based on the differences in starch digestion rates, protein content and amino acid profiles. Maize is more conducive to reduced-CP diets compared to wheat-based diets, although increased fat-deposition is markedly a shortfall of maize and sorghum-based diets. The factors influencing these differences stem from their compositional differences, namely their rate of starch digestibility, levels of non-starch polysaccharides (NSP) and protein. These have a flow on effect on starch and protein digestive dynamics and bird performance. Wheat has higher CP levels compared to maize which results in higher inclusions of unbound amino acids in wheat-based diets. The higher unbound amino acid levels in wheat-based, reduced CP diets may increase plasma ammonia levels following deamination of unbalanced, surplus amino acids. Various nutritional strategies were implemented to mitigate these known drawbacks. The inclusion of L-carnitine was found to be ineffective in mitigating fat deposition but may aid against ammonia overload through its antioxidative properties. Promise was observed in capping starch:protein ratios particularly in maize-based diets.