Effects of Diet Type and Ingredient Composition on Rate of Passage and Use of In Vitro Assays to Predict Amino Acid Digestibility of Animal Protein Meals in Broilers
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Ileal amino acid digestibility (IAAD) is used to characterize amino acid (AA) quality of animal protein meals (APM) for poultry, and IAAD assays utilize semi-purified (SP) diets. Nutrient utilization is influenced by rate of passage (ROP), and it has not been determined if differences exist in ROP between corn soybean-meal diets and semi-purified diets in IAAD assays. The IAAD assay is laborious and costly, and in vitro assays to predict IAAD of APM commonly used in the poultry industry would be useful tools for nutritionists. The first experiment evaluated the effects of diet type and ingredient composition on rate of passage (ROP) and apparent IAAD in broilers from 14 to 22 d of age. Experimental diets were formulated to contain 20% CP and consisted of: 1) corn-soybean meal-based (CSM) diet containing porcine meat and bone meal (MBM) (5% inclusion), 2) CSM diet containing distiller’s dried grains with solubles (DDGS) (5% inclusion), 3) SP diet containing MBM (38% inclusion), and 4) SP diet containing DDGS (76% inclusion). Time of 50% TiO2 excretion (T50) and mean retention time (MRT) indicated a faster (P < 0.05) ROP for SP-DDGS than the 2 CSM diets. There were no differences between T50 or MRT of SP-MBM and CSM-MBM. In general, apparent IAAD values were higher (P < 0.05) for the 2 CSM diets than for SP diets. The second experiment evaluated a novel digestive enzyme assay (Poultry Complete IDEA, Novus International, Inc., St. Charles, MO) (PC IDEA) and the pepsin digestibility assay as predictors of standardized IAAD of 20 APM fed to broilers from 25 to 30 d of age. Standardized IAAD, pepsin digestibility, and PC IDEA predicted digestibility were determined for 10 meat and bone meals and 10 animal protein blends. Pepsin digestibility and PC IDEA were both significantly correlated (P < 0.001) with SIAAD. Prediction equations for SIAAD of Lys, Met, and Thr were: % Lys SIAAD = [‒9.65 + (0.38 × % PC IDEA predicted Lys digestibility) + (0.69 × % pepsin digestibility)], % Met SIAAD = [‒35.95 + (0.62 × % PC IDEA predicted Met digestibility) + (0.75 × % pepsin digestibility)], % Thr SIAAD = [‒77.5 + (0.39 × % PC IDEA predicted Thr digestibility) + (1.37 × % pepsin digestibility)]. Values of R2 for Lys, Met, Thr, Val, and Ile were 0.46, 0.47, 0.55, 0.51, and 0.49, respectively.