Application of the law of diminishing returns for partitioning lysine and methionine intake between maintenance and growth in young broiler chicks

In the study presented here, the scope of a reparameterized monomolecular model was extended in growing young male chicks to provide an estimate of their lysine and methionine requirements for maintenance and growth. The equation was used with the NLMixed procedure of SAS to estimate parameters and combine them to determine other biological indicators. A number of criteria were used to evaluate general goodness of fit of the model, including model behavior, biologically meaningful parameter estimates and statistical performance. The estimated maintenance requirements and the determined values of lysine and methionine requirements for protein accretion were in good agreement with values reported previously by other researchers. Average efficiency of recovering lysine and methionine were greatest at low intakes and decreased as intakes increased. In conclusion, results presented here showed the applicability of the monomolecular equation to predict the magnitude and direction of responses of growing young broilers to dietary lysine and methionine intake without making any initial assumptions.