Amino Acid Nutrition and Metabolism in Chickens

Abstract

Both poultry meat and eggs provide high-quality animal protein [containing sufficient amounts and proper ratios of amino acids (AAs)] for human consumption and, therefore, play an important role in the growth, development, and health of all individuals. Because there are growing concerns about the suboptimal efficiencies of poultry production and its impact on environmental sustainability, much attention has been paid to the formulation of low-protein diets and precision nutrition through the addition of low-cost crystalline AAs or alternative sources of animal-protein feedstuffs. This necessitates a better understanding of AA nutrition and metabolism in chickens. Although historic nutrition research has focused on nutritionally essential amino acids (EAAs) that are not synthesized or are inadequately synthesized in the body, increasing evidence shows that the traditionally classified nutritionally nonessential amino acids (NEAAs), such as glutamine and glutamate, have physiological and regulatory roles other than protein synthesis in chicken growth and egg production. In addition, like other avian species, chickens do not synthesize adequately glycine or proline (the most abundant AAs in the body but present in plant-source feedstuffs at low content) relative to their nutritional and physiological needs. Therefore, these two AAs must be sufficient in poultry diets. Animal proteins (including ruminant meat & bone meal and hydrolyzed feather meal) are abundant sources of both glycine and proline in chicken nutrition. Clearly, chickens (including broilers and laying hens) have dietary requirements for all proteinogenic AAs to achieve their maximum productivity and maintain optimum health particularly under adverse conditions such as heat stress and disease. This is a paradigm shift in poultry nutrition from the 70-year-old “ideal protein” concept that concerned only about EAAs to the focus of functional AAs that include both EAAs and NEAAs.

The Dynamic Conversion of Dietary Protein and Amino Acids into Chicken-Meat Protein

“…Enzymatic digestion of protein by endogenous proteolytic enzymes and intestinal uptakes of amino acids along the digestive tract is reasonably well understood and a thorough review of protein digestion in poultry has been documented by Moran [ 43 ]. Additional reviews of protein digestion in poultry and livestock have been published by Krehbiel and Matthews [ 44 ], and in poultry specifically by He et al [ 3 ], while an instructive paper focusing on amino acid absorption in humans is recommended [ 45 ]. Importantly, the digestion and absorption of nutrients is an energy demanding process accounting for perhaps more than 20% of dietary energy [ 46 ].…”

“…Nevertheless, if reduced-crude protein (CP) diets could be developed so that a dietary reduction of 50 g/kg CP did not compromise growth performance, then the dietary protein to carcass protein ratio of 2.51 would decline to 1.89, a marked 24.7% improvement. The overall efficiency with which dietary amino acids are incorporated into chicken-meat, based on the data of He et al [ 3 ], is in the order of 55%, but this may vary from 35% to 70% for a given amino acid. Thus, this review considers the transition from dietary protein and amino acids to carcass protein in broiler chickens with the intention of identifying strategies to enhance the complex, kinetic processes involved.…”

Induction of gut leakage in young broiler chickens fed a diet with low rye inclusion

“…1995 ). In avian species, arginine generates a limited amount of citrulline via nitric oxide synthase, resulting in very negligible plasma levels ( He et al.,. 2021 ).…”

Understanding Nutrition and Metabolism of Threatened, Data-Poor Rheophilic Fishes in Context of Riverine Stocking Success- Barbel as a Model for Major European Drainages?

“…The study has proposed optimum dietary crude AA levels (i.e., green cells in Figure 2 A) and ideal protein concept [ 73 ] for juvenile barbels. Most importantly, considering all the 18 AAs together without discriminating between essential or non-essential ones (proposed paradigm shift; [ 32 , 89 , 90 ], is important to achieve extraordinary growth trajectory and significantly reduce the time required in captivity).…”