What « requirements » for essential amino acids in broiler chickens ? A critical survey of their determination and of some practical models

Abstract

To balance the feed levels in essential amino acids,nutritionists use tables containing average requirements stemming from bibliographical surveys. Result of experiments studying essential amino acid requirements, depend both on the criterion to be optimized (growth rate or feed efficiency) and on the methodologyadopted for analysing the results. From an experimentto the other, environmental conditions and chicken genotype may also explain a part of the observed variability of the requirements. To cope with this variability, the results from numerous experiments obtained mainly in fast growing broilers raised underoptimal conditions are pooled but the results of thosegrouped analyses are not precise, and this impairs the application of measured amino acid requirements tofield conditions. Mechanistic models integrating basic knowledge of the energy and protein metabolism mightconstitute additional tools to quantify the effects of an essential amino acid level on broiler performances under different conditions. Models not only synthesisethe knowledge acquired by various experiments butalso take simultaneously into account the multiple interactions among factors of variation. There are some marketed models measuring the effects of themain feed characteristics (essential amino acids, energy...) and raising conditions on chicken growth.Their results seem precise enough for an application but they are presented as "black boxes" and the complexities of their functioning make them difficult toupdate. INAVI is a model fully open to the user that might be more adapted to the diversity of production systems. Prediction of the growth of the chicken byINAVI is based on the effects of environmental and nutritional factors on feed intake regulation.