Effects of Diet Type and Ingredient Composition on Rate of Passage and Apparent Ileal Amino Acid Digestibility in Broiler Chicks

This experiment evaluated rate of passage (ROP) and apparent ileal amino acid digestibility (AIAAD) of 4 diets varying in ingredient composition fed to broilers from 14 to 22 d of age. Two hundred and 88 Ross × Ross 708 chicks (12 birds per cage; 0.45 m(2) per bird) were randomly assigned to 24 cages (6 replicate cages per treatment) at 1 d of age. Experimental diets were 1) corn-soybean meal-based (CSM) diet containing porcine meat and bone meal (MBM; 5% inclusion), 2) CSM diet containing distillers dried grains with solubles (DDGS; 5% inclusion), 3) semipurified (SP) diet containing MBM (38% inclusion), and 4) SP diet containing DDGS (76% inclusion). Diets were formulated to contain 20% CP and were adequate for vitamins and minerals. Experimental diets were provided from d 14 to 22. On d 18, a total excreta collection was conducted every hour for 12 h from 0800 to 1900 h to determine ROP, and AIAAD was determined on d 22. Time of 1% TiO(2) excretion (T1), 50% TiO(2) excretion (T50), and mean retention time (MRT) were used to express ROP. The SP-MBM diet reached T1 (P < 0.05) faster than the SP-DDGS or 2 CSM diets. However, T50 indicated a faster (P < 0.05) ROP for SP-DDGS than the 2 CSM diets, and no significant difference was observed between the 2 SP diets. The MRT of the SP-DDGS diet (5.13 h) was less (P < 0.05) than the MRT of the SP-MBM, CSM-MBM, and CSM-DDGS diets, which resulted in values of 5.48, 5.62, and 5.58 h, respectively. In general, the AIAAD values were higher (P < 0.05) for the 2 CSM diets than for SP diets. Except for His, no statistical differences were observed between the AIAAD of the 2 CSM diets. Comparing the 2 SP diets, AIAAD was usually similar or higher (P < 0.05) for SP-DDGS, except for His, Lys, and Gly, which were higher (P < 0.05) for SP-MBM. Based on T50 and MRT, SP diets containing DDGS had a faster ROP in broilers than CSM diets or SP diets containing MBM.