Attrition of amino acids in the life span of broiler chickens.

A dietary protein intake of approximately 2.5 kg is required to generate 1.0 kg of protein in the carcass of broiler chickens at 42 d post-hatch, reflecting the attrition or wastage of dietary amino acids that occurs during their lifespan. Thus, the aim of this review is to examine amino acid utilisation in broilers because the identification and correction of any avoidable losses will advantage both the chicken meat industry and consumers. Amino acids are lost to catabolic pathways in their transition across the enterocytes for energy production required for digestive processes. However, slowly digestible starch has been indicated to spare amino acids from catabolic losses by providing more glucose as an alternative energy substrate. This potential benefit warrants further investigation. Protein turnover may represent an even greater source of amino acid attrition, but it is a complex area. Protein turnover refers to the dynamic equilibrium between protein deposition and degradation, with a positive balance indicating net protein synthesis and growth. 3-Methylhistidine concentrations in systemic plasma may be a sufficiently accurate indicator of protein degradation, which is probably the more influential component in protein turnover. If this can be demonstrated, experiments involving both L-carnitine and 3-methylhistidine may prove highly instructive because there are indications that L-carnitine has the capacity to depress protein degradation and enhance protein turnover in broiler chickens. The function of insulin in avian species is essentially a conundrum, particularly in relation to its regulatory role over protein turnover as broilers mature, and, ideally, this should be elucidated. Importantly, nutritionists should continue to endeavour to formulate diets for broiler chickens that meet amino acid requirements accurately. When this is achieved, circulating ammonia levels arising from post-enteral amino acid imbalances will be limited to the advantage of protein turnover and broiler growth performance. It is possible that protein degradation would be attenuated by broiler diets with appropriate balances between protein-bound and non-bound entities, ideal amino acid ratios and higher dietary electrolyte balances.