The concept of a requirement for dietary protein has been controversial since it was discovered
that proteins are composed of amino acids and that some amino acids are dietary essentials
for maximum growth and performance. In addition to the 10 essential amino acids and 3 that
can be accreted only from limited substrates, poultry need a quantity of amino acids to synthesize
the other 8 that are needed to synthesize body proteins. Adding purified amino acids or
amino acid precursors has been known for more than 50 yr to allow for reduced levels of intact
proteins to provide adequate levels of essential and nonessential amino acids (CP). It has been
recognized that individual essential amino acid requirements are functions of the total CP level.
Increasing the total CP level while maintaining ideal ratios of essential amino acids increases
growth, feed utilization efficiency, and carcass yields (i.e., decreases carcass fat). A published
data set is used here to demonstrate 1) that potential problems arise from analyzing combined
data sets inappropriately; 2) that in the overwhelming majority of studies, there is a positive
response in growth (P < 0.0002) and feed utilization efficiency (P < 0.0002) to increasing dietary
protein levels; 3) that the relationships are much stronger in faster growing broiler strain
birds; and 4) that there is no clear break point or “requirement” for CP in the range of dietary
protein levels typically studied. Regardless of whether it is called “CP level” or “essential +
nonessential amino acid level,” there is no clear requirement, only a smooth response curve that
approaches maxima at lower levels for growth, and then feed utilization efficiency, and then
lean meat yield, and finally the minimum for carcass fat. As a result, decisions on feeding levels
for essential and nonessential amino acids should depend on the input-output relationships and