The influence of feed ingredients on CP and starch disappearance rate in complex diets for broiler chickens

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.