Implications of elevated threonine plasma concentrations in the development of reduced-crude protein diets for broiler chickens

Abstract

There is a real quest to develop reduced-crude protein diets to facilitate sustainable chicken-meat production. However, pronounced elevations in threonine plasma concentrations in systemic plasma have consistently been observed pursuant to crude protein reductions in diets for broiler chickens. The aim of the present Perspective was to consider the genesis and consequences of these elevated threonine concentrations. A series of five reduced-crude protein feeding studies with maize-based diets completed on the Camden Campus of Sydney University was the basis of the present Perspective. Collectively, an average reduction in dietary crude protein from 212 to 167 g/kg generated a mean increase of 64.8% (867 versus 526 μmol/L) in threonine plasma concentrations. This was attributed to the downregulation of hepatic threonine dehydrogenase activity, which catalyses threonine to acetyl-CoA and glycine and a mechanism for this inhibition is proposed. Tangible reductions in dietary crude protein usually impair feed conversion efficiency and increase fat deposition. Threonine plasma concentrations are elevated by these reductions and the likelihood is that threonine concentrations may be an indicative biomarker of the precision with which efficient reduced-CP broiler diets are formulated and, if so, would facilitate their successful development.