An overview of energy and protein utilisation during growth in simple-stomached animals

Abstract

The biological processes underlying the partitioning of amino acids and energy during animal growth are well understood qualitatively. However, if a deeper mechanistic understanding is to be achieved, such as to allow generalised predictions of growth outcomes, these biological processes need to be described quantitatively, along with critical control points. Concepts and rules can be formulated at mechanistic and semi-mechanistic levels, and often reflecting causation, to allow nutrient intake and partitioning to be described in a quantitative manner for different animal and environmental conditions. An overview is given of amino acid and energy partitioning during growth in monogastric animals, in terms of causation and quantitatively based descriptors. Current knowledge is far from complete, and areas requiring new insights and a more in-depth understanding of causative mechanisms include voluntary food-intake control, dynamics of nutrient uptake, temporary post-prandial nutrient storage, relationships among nutrient intakes, protein turnover and maintenance-energy requirement, colonic amino acid uptake in poultry, bioavailability of amino acids other than lysine, diet effects on gut endogenous amino acid loss, inevitable amino acid catabolism, preferential amino acid catabolism, and diet, age and genotype effects on body protein synthesis and degradation.