Amino acids requirements

The term "requirement" is usually defined for growing animals as the minimum supply of an amino acid that maximizes growth. Amino acids requirement can be estimated through dose-response studies, but reported results can be quite variable. A part of this variability comes from the way of expressing the requirement and the method used to interpret the results which are not always in line with the objective and the protocol of the trial (see "Estimating amino acid requirements through dose-response experiments in pigs and poultry - Protocol and results interpretation"). That is why using compilations of numerous trials and adequate modeling methods is necessary to estimate an amino acid requirement that can be considered as a recommendation for a given growing stage.

Amino acid requirements are often expressed based on the concept of the ideal protein. For a given stage of production, the ideal amino acid profile (i.e., the composition of ideal protein) is generally considered to be constant. This means that only variation in the lysine requirement (per kg of feed) has to be accounted for in feed formulation when the other indispensable amino acids are expressed as a percentage of lysine.

To better estimate the amino acid content which will be really available for animals, amino acids requirements are expressed on a standardized ileal digestible (SID) basis for swine and on a true digestible (TD) basis for poultry.