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PHOSPHORUS DIGESTIBILITY RESPONSES OF BROILER CHICKENS TO HEAT TREATMENT OF FEEDSTUFF, AND DIFFERENT PROTEIN SOURCES
This thesis aimed to evaluate the effect of heat treatment of different ingredients on their respective phosphorus digestibility and assess the impact of protein source in the basal diet on the regression-derived phosphorus digestibility methodology. Two studies were carried out to evaluate the objectives.
In study 1, regression-derived ileal digestibility and utilization coefficients of phosphorus (P) responses to autoclaving soybean meal (SBM) or poultry meal (PM) were investigated in two experiments. On day 19 post hatching male Cobb 500 broiler chickens were individually weighed and allotted into 6 or 5 treatments in experiment (Exp.) 1 or 2, respectively, in a randomized complete block design, with 8 replicate cages and 8 birds per cage in both experiments. In Exp. 1, diets were formulated with either non-autoclaved or autoclaved soybean meal at 380, 480, or 580 g/kg in a 2 file:///C:/Users/vshae/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png 3 factorial arrangement. Experiment 2 consisted of a basal diet and other four diets, with 40 or 80 g/kg of non-autoclaved PM or autoclaved PM arranged as a 2 file:///C:/Users/vshae/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png 2 + 1 factorial. Chromic oxide was added as an indigestible index marker to determine nutrient ileal digestibility and retention. Birds received the experimental diets for 3 days, and excreta collection was conducted during the last two days. All birds were euthanized by CO2 asphyxiation, and ileal digesta samples were collected. Data were analyzed using the GLM procedure. In both studies autoclaving decreased (P < 0.05) DM digestibility and retention. Increasing the inclusion level of test ingredients linearly increased (P < 0.05) intake of digestible and utilizable P in both studies and linearly reduced the digestibility and retention of DM and P in the soybean meal study. Autoclaving 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 autoclaved PM were 45, 53.6, 61.2 and 61.2%, respectively, and the corresponding retention were 40.6, 45, 51.7, and 59.2%. Autoclaved SBM tended (P = 0.058) to have higher P digestibility than non-autoclaved, but no effect was noted with PM. These results indicated that autoclaving feed ingredients reduced the digestibility and retention of dry matter, and the digestibility of phosphorus of soybean meal may be improved by heat treatment but not that of poultry meal, which may be due to phytate P degradation.
The second study was conducted to evaluate the effect of varying protein sources in the basal diet on the regression-derived P digestibility in soybean meal. This experiment was organized in a 4 × 3 factorial arrangement, consisting of 4 diet types that differed in their protein sources; with the test ingredient as the only source of protein, or with one of 3 protein supplements (casein, potato protein isolate (PPI) or dried egg albumen (DEA)) added at 60 g/kg, and 3 levels of test ingredient (SBM) inclusion at 290, 370 or 450 g/kg. Male Cobb 500 broiler chickens were individually weighed and distributed in the 12 treatments in a randomized complete block design, with 8 replicate cages and 6 birds per cage on day 19 post hatching. Birds were fed the experimental diets for 3 days, and ileal digesta and excreta samples were collected similarly to the first study. Diet type affected (P < 0.01) the digestibility and total tract retention of DM, P, N, and Ca. Diets with added casein presented the highest (P < 0.05) digestibility of P, Ca, and N, retention of P and Ca, and intake of digestible and utilizable P. The digestibility and retention of DM linearly decreased (P < 0.001) with increasing inclusion levels of SBM in all diet types. The estimated ileal digestibility of P in SBM was 56.9, 62.6, 59.1, and 36.4% for diets without protein supplements, with casein, PPI, or DEA, respectively; the corresponding retention of P were 51.7, 82.6, 42.7, and 52.2%. Diet type affected (P < 0.05) the slope and intercept of P digestibility in SBM. A comparison of the coefficients using confidence intervals demonstrated that the ileal digestibility of P in SBM determined in diets with DEA was lower (P < 0.05) than in the other diet types, which were not different from one another. These results indicate that the selection of dietary protein supplements may affect P digestibility essays using the regression method.
In summary, the digestibility of P in soybean meal may be improved by heat treatment while not that of poultry meal, which may be ascribed to the higher phytate P content of SBM, and phytate degradation from heat treatment. Results from the second study demonstrated that the protein source, but not level in the basal diet affects the P digestibility of the essay ingredient determined using the regression method. These findings can contribute to reducing P excretion by enhancing the formulation of broiler diets on a digestible P basis, providing information on the effect of heat treatment on dietary P availability, and refining the methodology used to determine P digestibility.
- Master of Science
- Animal Sciences
- West Lafayette