A Model to Describe the Genetic Potential for Nitrogen Deposition and Estimate Amino Acid Intake in Poultry

The maximum protein or nitrogen deposition is commonly used as the basis for modeling the amino acid intake in growing birds. In previous studies, the exponential functions of the nitrogen balance data were used to estimate the theoretical maximum for nitrogen deposition (NDmaxT) as a reference model for the amino acid intake. However, this amino acid intake value is only valid for the period in which the NDmaxT was estimated. Additionally, physiological changes, such as the rapid development of reproductive organs and associated increases in protein deposition that occur in the period before the first egg is laid, should be considered in the models. Thus, this study was conducted to model the daily NDmaxT of pullets and integrate this value into the factorial model to estimate the daily methionine + cysteine (Met+Cys) intake. Our results showed that, up to 63 days of age, the values of NDmaxT obtained via the modeling procedure were 11% higher than the values predicted using the Gompertz function. At 105 days, there was a protein deposition peak from the growth of the reproductive organs, which contributed 14% of the variation in the model in this age. Alongside these factors, the integration of the models enabled daily Met+Cys estimates consistent with the literature; however, the recommendations varied according to the targeted daily protein deposition (50% or 60% of NDmaxT), daily feed intake, and amino acid utilization efficiency. The modeling approach demonstrated here for Met+Cys can be used to model other amino acid requirements and can be extended to other species.