Application of the law of diminishing returns to estimate maintenance requirement for amino acids and their efficiency of utilization for accretion in young chicks

Suitability of the monomolecular equation, specifically re-parameterized for analysing energy balance data, has recently been investigated in broilers and turkeys. In the current study, this equation was applied to literature data from growing chicks fed crystalline amino acid (AA) diets, in order to provide estimates for AA requirements for maintenance, body-weight gain and protein accretion. Non-linear regression was used with the data to estimate parameters and combine them to determine other biological indicators. The predictive ability of the model was evaluated with reference to model behaviour when fitting the data, biologically meaningful parameter estimates and statistical performance. The model estimated the maintenance requirements for valine, threonine and lysine to be in the range 80-111, 96-109 and 52-209 mg/kg of liveweight/day, respectively, depending on the response criterion. Requirements for maintenance were in good agreement with values reported previously. Average efficiency of recovering AAs in whole body protein, between maintenance and four x maintenance, was in the reported range of 0.80-1.0 and greatest at low intakes and decreasing as intakes increase.