Modelling of protein metabolism yields amino acid requirements dependent on dietary amino acid efficiency, growth response, genotype and age of growing chicken

Four separate nitrogen balance experiments with fast and slow growing genotypes of growing chicken were conducted to yield basic data for modelling of lysine and threonine requirements dependent on genotype, age, protein deposition and dietary amino acid efficiency. A total of 1008 individual nitrogen balance data in up to four age periods (I: 10-25 days; II: 30-45 days; III: 50-65 days; IV: 70-85 days) was utilised. According to principles of the diet dilution technique, experimental diets provided graded protein supply (60-360 g.kg(-1) crude protein) with lysine or threonine as the first limiting amino acid. The modelling procedure utilised currently observed model parameters for the theoretical potential of nitrogen retention (NRmaxT) and nitrogen maintenance requirement (NMR), respectively. The selected results of the applied modelling procedure are discussed in comparison with current recommendations for growing chickens and aspects of different procedures utilised for assessing quantitative amino acid requirements, respectively. The amino acid requirement data yielded by modelling were in line with current recommendations, but are not directly comparable due to discrepancies in the applied procedures. However, the concluded requirements for lysine and threonine are useful to improve actual predictions for ideal amino acid ratio'' in growing chickens which are in focus of on-going studies.