NDF is a measure of carbohydrate in plants and refers to the parts left when the plant material is refluxed (boiled) in a neutral detergent solution. This equates to the structural parts of plant cell walls and includes cellulose, hemicellulose, and the woody material lignin all of which provide structural strength and rigidity to the plant. When NDF is low, intake increases and as the plant matures, NDF values rise, and intake of the more fibrous plant tends to decrease.
NDF requires microbial fermentation for digestion. As NDF rises, other carbs like starch and sugars (NSC) tend to fall, along with protein. So, for example, a mature hay with a high NDF value may be more suitable for horses prone to Insulin Resistance or Laminitis than hay made from an early cut sward with lower NDF and high NSC value. NDF values in the range 40% to 50% are regarded as suitable for performance horses and stud use whereas older spelling horses may do perfectly well on hay with higher NDF values, though anything over 65% NDF has little energy value for horses.
When using NDF to gauge forage quality it should be evaluated in conjunction with the Acid Detergent Fibre ADF value.
See also ADF.