Dietary requirements of synthesizable amino acids by animals: a paradigm shift in protein nutrition

Abstract

Amino acids are building blocks for proteins in all animals. Based on growth or nitrogen balance, amino acids were traditionally classified as nutritionally essential or nonessential for mammals, birds and fish. It was assumed that all the “nutritionally nonessential amino acids (NEAA)” were synthesized sufficiently in the body to meet the needs for maximal growth and optimal health. However, careful analysis of the scientific literature reveals that over the past century there has not been compelling experimental evidence to support this assumption. NEAA (e.g., glutamine, glutamate, proline, glycine and arginine) play important roles in regulating gene expression, cell signaling, antioxidative responses, fertility, neurotransmission, and immunity. Additionally, glutamate, glutamine and aspartate are major metabolic fuels for the small intestine to maintain its digestive function and to protect the integrity of the intestinal mucosa. Thus, diets for animals must contain all NEAA to optimize their survival, growth, development, reproduction, and health. Furthermore, NEAA should be taken into consideration in revising the “ideal protein” concept that is currently used to formulate swine and poultry diets. Adequate provision of all amino acids (including NEAA) in diets enhances the efficiency of animal production. In this regard, amino acids should not be classified as nutritionally essential or nonessential in animal or human nutrition. The new Texas A&M University’s optimal ratios of dietary amino acids for swine and chickens are expected to beneficially reduce dietary protein content and improve the efficiency of their nutrient utilization, growth, and production performance.

Effects of low-protein diets supplemented with indispensable amino acids on growth performance, intestinal morphology and immunological parameters in 13 to 35 kg pigs

“…In addition, pigs can synthesize arginine with precursors such as glutamine, glutamate and proline (Wu, 1997), the lower level of these precursors may be responsible for the lower plasma concentration of arginine. It is implied that dietary protein level can affect immune function of animals and humans (Ruth and Field, 2013 (Wu, 2014). In this study, glutamate and aspartate were only 59% and 54% of that in control diet, respectively.…”

“…Consistently, a recent study by Powell et al (2011) demonstrated that growth performance of pigs (20-50 kg) could be maintained when dietary CP level was reduced by~5% units with the supplementation of IAA. Moreover, Wu (2014) emphasized both IAA and DAA should be taken into consideration in the formulation of balanced diets to maximize protein accretion in animals. It was reported that generation of DAA in pigs would be reduced by a deficiency of total N in low-CP diet (Columbus et al, 2012), and become a limiting factor for normal growth of pigs (Gloaguen et al, 2014).…”

“…It is also reported that some of the traditionally classified DAA (e.g. glutamate and arginine) play important roles in maintaining normal immunity, which is indeed lower in the low-CP diets (Wu, 2014).…”

<b>Effect of oral dietary supplement for chicks subjected to thermal oscillation on performance and intestinal morphometry

“…Some authors (Geyra et al, 2001;Wu, 2014) have already evaluated oral nutritional supplementation in young birds and observed an increase in weight gain only in the third week of life of birds, which were maintained under thermal comfort in the first week of life. They concluded that the amino acids provided were directly involved in the processes of intestinal ontogeny.…”

“…However, nutritional supplements of amino acids with relevant participation in the regulation of gene expression, cellular signaling, antioxidant responses, neurotransmission, and immunity can contribute directly to these processes. Moreover, amino acids such as glutamate, glutamine and aspartate are important metabolic fuels for the small intestine to maintain digestive function and to maintain the integrity of the intestinal mucosa (Wu, 2014).…”