amino acid density, amino acid digestibility, protease, turkey


Protein is one of the most expensive nutrients in poultry diets. In an effort to minimize feed costs, protein digestion and utilization by the animal must be carried out as effi­ciently as possible. The objective of this experiment was to evaluate the effects of dietary amino acid density and exogenous protease inclusion on growth performance and amino acid digestibility in turkey poults. Hybrid turkey poults (n = 780) were fed diets formulated to provide low (LAA) or adequate (AAA) amino acid density (approxi­mately 91 and 100% of the NRC4 recommended requirement for digestible Lys, respec­tively) with each diet being fed with or without an exogenous protease. Poults received experimental diets from d 1 to 42 of age. Growth performance metrics were calculated from pen weights and feed consumption was 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. For the overall experiment (d 0 to 42), poults fed AAA diets had improved (P < 0.01) ADG, ADFI, and feed conversion ratio (FCR) compared to those fed LAA diets. There was no difference (P > 0.14) in poult performance due to protease inclusion. There was an amino acid density × protease interaction (P = 0.01) for apparent ileal amino acid digestibility (AIAAD) of Trp. There was no difference in AIAAD coefficients of Trp in the LAA diets with or without protease. However, in the AAA diets, poults not receiving protease had greater AIAAD of Trp than those consuming protease. There was no difference (P > 0.09) in AIAAD coefficients of Arg, Met, Cys, Thr, Ile, Leu, Lys, or Val due to dietary amino acid density or protease inclusion. Greater amino acid density improved growth performance in poults up to 42 d of age. No improvement in growth performance was observed when poults were fed an exogenous protease in the starter phase, although protease inclusion increased ADG by 5.3% and ADFI by 4.1% during the grower phase. There was no benefit of increased dietary amino acid density or protease inclusion on AIAAD in poults.


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