Associated effect among feed ingredients and its application in feed formula design

In the formulation of rations and the feed evaluation systems it is assumed that nutrients from different feeds are additively on the base of their assigned nutritive value, irrespective of feeding level or other components of the diet. However, these assumptions are not always valid because there are interactions in the digestibility or in the efficiency of the utilization of dietary energy caused by mixing the components of the diet. The interactions of feeds can affect the nutritive value, so the additivity is not always effective. Interactions among feeds are of economic importance but they can rarely be identified by conventional analyses of feeds. This emphasizes the need to make greater use of animal based feed evaluation systems and to manipulate the interactions correcting the negative ones and exploiting the positive ones, when developing livestock feeding systems based on the imbalanced feed resources (crop residues and byproducts) available in China. In this paper the associative effects of feeds on the digestion of nutrients and the balance among absorbed nutrients as well as the possible mechanism of these effects were discussed.