Modelling of lysine requirement in broiler breeder hens based on daily nitrogen retention and efficiency of dietary lysine utilization

The current feeding programs used for broiler breeder hens need information on how to make use of the genetic potential more efficiently by modelling the amino acid (AA) requirements. Thus, this study aimed to determine the model parameters for maximum nitrogen retention (NRmaxT), nitrogen maintenance requirement (NMR) and the efficiency of lysine utilization (bc−1) to determine the lysine (Lys) requirements of broiler breeder hens. Nitrogen balance trials were performed in two periods (I: 31-35 wks and II: 46-50 wks). Seven dietary treatments were used with eight replicates and one hen per cage; the treatments consisted of seven diets with protein levels ranging from 58.8 to 311.9 g/kg of feed, with Lys being limiting in the dietary protein (c = 3.91 g of Lys in 100 g of CP). For each period, nitrogen intake (NI), nitrogen excretion (NEX), nitrogen in egg mass (NEM), nitrogen deposition (ND) and nitrogen retention (NR, NR = ND + NEM + NMR) were obtained in a N balance trial of 25 days. The NMR was calculated as the intersection point of the exponential curve between NEX and NI at NI = 0. The NRmaxT and b (slope related to protein quality) were estimated by the exponential fit between NR and NI. The Lys efficiency bc−1 was obtained dividing b by c. The likelihood ratio test for the model parameters yielded 255 mg/BWkg0.67 for NMR, 0.000117 for b and 1684 mg/BWkg0.67 (period I) and 1484 mg/BWkg0.67 (period II) for NRmaxT. The necessary Lys intake dependent on NR and Lys efficiency was derived by the equation Lys = (lnNRmaxT-ln(NRmaxT-NR))/(16 × bc−1). Lys intakes required to achieve 0.80 times the maximum potential (NRmaxT) were 915 mg and 876 mg in the period I and II, respectively. For broiler breeder hens, assuming 0.80 times the NRmaxT value and average efficiency of Lys utilization, 6.02 g/kg (31-35 wk) and 5.96 g/kg (46-50 wk) digestible dietary Lys were observed as optimal digestible Lys concentration in the diet (corresponding to 152 and 147 g of daily feed intake, respectively). Results of model calculations need verification in performance trials with evaluation of nitrogen deposition and varying dietary Lys efficiencies.