Lysine exerts specific effects on body composition at dietary levels higher than that required for maximum growth rate, which also results in an improved feed conversion ratio (FCR). As a consequence of these differences, it becomes apparent that there is a hierarchy of requirements. The requirement for maximum gain is lower than that for breast meat (BM) yield, which is lower than the requirement for FCR; and lastly, the requirement for minimum abdominal fat (AF) percentage is the highest of all. Threonine, on the other hand, does not appear to exhibit so pronounced an effect on body composition, whereas, in the case of valine, these effects seem to be absent. These different effects of lysine, threonine, and valine can induce different amino acid requirement profiles according to the criteria used for determining the requirement. Moreover the particular mathematical model being used to calculate amino acid requirements can also influence amino acid requirement profiles.