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A proportional mixture design was used to systematically create a total of 56 diets using ten feed ingredients. Diets differed widely with regards to chemical characteristics and ingredient inclusion levels. Apparent ileal digestibility of energy and protein of the diets were determined in broiler growers fed ad libitum from 21 to 24 d post-hatch. The chemical composition and the in vivo digestibility values were used to establish prediction equations for energy and protein digestibility, using multivariate data analysis. Root mean square error as percentage of the observed means (RMSE%) and residual error were used to evaluate the strength and accuracy of the predictions and to compare predictions based on chemical characteristics with estimates based on table values. The estimates of ileal digestibility of energy from table values were relatively accurate (RMSE% = 5.15) and was comparable to those predicted based on the chemical composition of diets. Estimates of ileal digestibility of protein based on table values were less accurate (RMSE% = 8.21); however, the prediction was improved by multivariate regression (RMSE% = 5.46) based on chemical composition of diets. The best predictors for ileal energy digestibility were starch, crude fiber and phytate contents (P < 0.01) and the best predictors for crude protein digestibility were starch, CF and fat contents (P < 0.05). In conclusion, the ileal digestibility of energy can be accurately predicted using table values; however, the accuracy of prediction of the ileal digestibility of protein can be improved when chemical characteristics of the diet are considered., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The influence of feed ingredients on digestion kinetics of N and starch in complex diets was investigated in the current experiment. A total of 34 diets with different inclusion levels of 10 commonly used feed ingredients (corn, wheat, sorghum, soybean meal, canola meal, full-fat soybean meal [FFSB], palm kernel meal, meat and bone meal, wheat distillers grain with solubles and wheat bran) were randomly allocated to 170 cages with 8 birds in each. Apparent jejunal and ileal digestibility of N and starch was determined on a cage level in broilers feed the experimental diets ad libitum from 21 to 24 d after hatch. Disappearance rate of N and starch from the intestine was estimated through a first-order decay function fitted to the digesta data from the jejunum and ileum. The fit of the decay functions was evaluated with root mean squared error as percentage of the observed mean. The influence of the feed ingredients on the disappearance rates were found through a linear regression model, including the effect of the single ingredients, 2-way and 3-way interactions and evaluated with a Student t test test. Starch digestion kinetics were in general faster than N digestion kinetics. The N disappearance rate was both influenced by single ingredients and interaction amongst ingredients, whereas starch disappearance rate mainly was influenced by single ingredients. A combination of FFSB and soybean meal decreased the N digestion rate by 22 to 25% compared with diets with only soybean meal or FFSB, respectively. These results indicate that nutrients from 1 feed ingredient can influence the rate of disappearance of nutrients from other feed ingredients in a complex diet. This highlights the importance of understanding nutrient digestion kinetics and how these are influenced both additively and nonadditively by different feed ingredients in complex diets., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)