Effects of Assay Methodology and Standardization for Endogenous Losses of Energy on Determination and Additivity of Metabolizable and Digestible Dietary Energy for Broilers
Type of DegreePhD Dissertation
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Efficient broiler production requires providing birds with diets with appropriate energy density. A lack of additivity of dietary energy could lead to under- or over-supplying energy to broilers. Additivity may be affected by assay methodology, standardization for endogenous losses of energy (EEL), or the energy calculation. A series of experiments was conducted to evaluate diet suitability for estimating EEL, determine effect of assay methodology and energy calculation on individual feed ingredients, and to assess effect of these techniques on additivity of ingredient energy in blended diets. In Chapter 3, Experiments 1 and 2 were conducted to determine a diet appropriate for estimation of EEL in broilers. Broilers were provided with semi-purified diets (8 replicate cages per dietary treatment) from 18 to 23 D of age. At 23 D of age, ileal digesta was collected and evaluated for the presence of glucose. Gross energy and TiO2 concentrations were measured to determine EEL. Differences in EEL were compared utilizing ANOVA and regression. In Experiment 1 (Chapter 3), broilers were provided with diets primarily composed of dextrose, dextrose and cellulose, starch and dextrose, or starch, dextrose, and casein. In Experiment 2 (Chapter 3), broilers were provided with dextrose-based diets containing 0, 5, 10, or 15% casein. Based on these experiments, a dextrose-based diet containing 10% casein is appropriate for estimating EEL as it minimizes ileal glucose recovery (P < 0.0001) while allowing broilers to maintain BW (P < 0.0001). In Chapters 4 and 5, a series of 3 experiments was conducted to evaluate effect of methodology and calculation on additivity. In each experiment, broilers were provided with experimental diets (16 replicate cages per dietary treatment) at 18 D of age, a 48-h balance study was conducted from 21 to 23 D of age, and ileal digesta was collected at 24 and 25 D of age. Gross energy, TiO2 concentration, and CP were determined in dried feed, digesta, and excreta samples to determine AME, AMEn, standardized ME (SME), apparent ileal digestible energy (AIDE), and standardized ileal digestible energy (SIDE). Differences in energy were analyzed utilizing ANOVA and contrasts, while additivity was assessed utilizing a 1-sample 1-side T-test where H0=0. Significance was considered P ≤ 0.05, while additivity was determined when P > 0.05. Three experiments evaluated energy in cereal grains or soybean meal (SBM). Experiment 1 (Chapters 4 and 5) determined energy of corn and wheat or SBM utilizing the direct method. Experiment 2 (Chapters 4 and 5) determined energy of corn or SBM utilizing the direct method as well as the substitution method at two substitution rates (15 and 30% for corn; 10 and 20% for SBM). Experiment 3 (Chapters 4 and 5) determined the energy of corn or SBM utilizing the direct method and the substitution method (20 and 30% substitution for corn and SBM, respectively). The direct method underestimated the determined energy of both corn and SBM compared with the substitution method (P ≤ 0.0032). In Chapter 6, 2 experiments evaluating effects of assay methodology and energy calculation on additivity of ingredients were conducted. Additivity was determined (P ≥ 0.08) using AME, SME, AIDE, and SIDE when determined based on the substitution method, but not (P ≤ 0.0019) when determined based on the direct method. These experiments indicated that methodology affects determined energy of corn and SBM, which then impacts the additivity of energy. However, standardization for EEL did not provide energy values more additive than apparent values.