Regression-derived phosphorus digestibility responses of broiler chickens to heat treatment of soybean meal and poultry meal

Two studies were conducted to evaluate the effects of autoclaving soybean meal (SBM) or poul-try meal (PM) on their respective regression-derived phosphorus (P) ileal digestibility and utilization coeffi-cients. On day 19 post hatching 384 or 320 Cobb 500 male broiler chickens were individually weighed and allotted into 6 or 5 treatments in Experiment 1 or 2, respectively. Both experiments consisted of 8 replicate cages with 8 birds per cage in a randomized complete block design. In the first study, 6 diets were formulated with either non-autoclaved or autoclaved soybean meal at 380, 480, or 580 g/kg in a 2 x 3 factorial. The second consisted of 5 diets including one corn-soybean meal and cornstarch based basal diet and 4 diets with 40 or 80 g/kg of non-autoclaved PM or autoclaved PM (APM). Chromic oxide was added as an indigestible index to determine the ileal digestibility and retention of nutrients. Birds received the experimental diets for 3 d and excreta collection was conducted during the last 2 d. At the end of the experiments all birds were euthanized by CO2 asphyxiation and ileal digesta sam-ples were collected. Data were analyzed by ANOVA using the GLM procedure. In both studies autoclaving decreased (P < 0.05) DM digestibility and retention. Increasing the inclusion level of test ingredients caused a linear increase (P < 0.05) in intake of digestible and utilizable P in both studies, and linear reductions in the digestibility and retention of DM and P in the soybean meal study. Inclusion of autoclaved SBM resulted in higher (P < 0.01) ileal digestibility of P and retention of P and Ca. The estimated ileal digestibility of P in SBM, autoclaved SBM, PM and APM were 45, 53.6, 61.2, and 61.2%, respectively, the corresponding reten-tion were 40.6, 45, 51.7, and 59.2%, respectively. Comparison of the regression coefficients revealed that autoclaved SBM tended (P = 0.058) to have higher P digestibility than non-autoclaved while no effect was noted with PM.