Abstract: Fiber in the diet has multiple physiological responses of ruminant to chemical characteristics, and chewing activity, rumen fermentation, milk fat percentage and healthy status associated with physical characteristics. In this review, physically effective neutral detergent fibre served as an indicator of physical and chemical characteristics of fiber in the diet is consist of definition, connotation and estimation methods. This research progress also reviewed the effects of physically effective neutral detergent fibre on feed intake, chewing behavior, rumen fermentation, and lactation performance by ruminant.

Key words: ruminant; physically effective neutral detergent fibre; rumen fermentation; lactation performance