Abstract
Three experiments were conducted to determine the effects of age on apparent MEn and apparent amino acid (AA) digestibility of various diets for New Hampshire × Columbian (Experiments 1 and 2) and commercial broiler (Experiment 3) male chicks. Excreta were collected at 0 to 2, 3 to 4, 7, 14, and 21 d of age in all experiments, and nutrient digestibility was determined using acid-insoluble ash as a marker. The first experiment evaluated a corn-soybean meal (SBM) diet. Both MEn and digestibility of AA increased with age, and broken-line regression analysis predicted a plateau at 14 d for MEn and 10 d of age for AA digestibility. For example, MEn increased from 2,970 to 3,430 kcal/kg DM, and lysine digestibility increased from 78 to 89% between 0 and 14 d of age. The second experiment evaluated cornstarch-crystalline AA, dextrose-casein, corn-SBM, and corn-canola meal diets. The MEn of the corn-SBM, corn-canola meal, and cornstarch-crystalline AA diets increased from 0 to 14 d of age. In contrast, the MEn of the dextrose-casein diet was high (3,800 kcal/kg DM) immediately after hatching and did not increase substantially with increasing age. Digestibility of AA increased with age for the corn-SBM and corn-canola meal diets, and broken-line regression analysis again predicted a plateau at approximately 10 d of age. Conversely, AA digestibility of the dextrose-casein and cornstarch-crystalline AA diets was high immediately after hatching (93 to 96%) and increased only slightly with age. The results of Experiment 3 with commercial broiler chicks also showed significant (P < 0.05) increases in MEn and AA digestibility with increasing age. The results of this study indicated that the MEn and AA digestibility of corn-SBM and corn-canola meal diets increase with age for young chicks. The results also showed that MEn and AA digestibility were very high for a dextrose-casein diet immediately after hatching. Thus, the latter ingredients may have beneficial effects for very young chicks.
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