Nutritional function of undigested neutral detergent fiber in ruminant

The undigested neutral detergent fiber (uNDF) is a portion of neutral detergent fiber that cannot be fermented and utilized by the microorganisms in the rumen. However, it plays an important role in the growth and metabolism of ruminants. Therefore, optimal level of uNDF in the diet is crucial for the nutrition and health of ruminants. In this paper, we reviewed 1) the nutritional functions of uNDF, including feeding behavior, rumen function, NDF digestibility, and diet formulation; 2) uNDF determination method; 3) application of uNDF in diet formulation in order to provide reference and theoretical basis for the health and efficient production of ruminants.