Effects of dietary amino acid density and exogenous protease inclusion on growth performance and apparent ileal amino acid digestibility in poultry

Two experiments were conducted to evaluate the effects of dietary amino acid density and exogenous protease inclusion on growth performance and amino acid digestibility in poultry. In experiment 1, Cobb 500 broiler chicks (n = 480) were fed to 21 d of age. Treatments were arranged as a 2 × 4 factorial design with main effects of commercial protease (with or without) and amino acid density which corresponded to approximately 95, 97.5, 100, or 102.5% of breeder recommendations for digestible Lys. In experiment 2, hybrid turkey poults (n = 780) were fed diets formulated to provide low or adequate amino acid density (approximately 91 and 100% of the NRC-recommended requirement for digestible Lys, respectively) with each diet being fed with or without an exogenous protease. Poults received experimental diets from day 1 to 42 of age. Growth performance metrics were calculated from pen weights and feed consumption recorded throughout each experiment, and digestibility data were obtained from analysis of ileal contents. Data were analyzed using SAS 9.4 with pen as the experimental unit and pen location as the blocking factor. Results of these experiments demonstrated broilers fed 1.12 and 1.21% digestible Lys diets with added protease had a 2-point improvement in feed conversion ratio (FCR) compared with chicks fed these diets without protease. Increasing amino acid density improved FCR in broilers and poults and improved BW, ADG, and ADFI in poults. There was no evidence that added protease had an effect on BW, ADG, or ADFI in broilers or poults. Finally, ileal amino acid digestibility was not affected by amino acid density or protease inclusion for either 20-day-old broiler chicks or 42-day-old turkey poults.