Physically effective fibre (peNDF)

Physically effective fibre is the portion of the fibre in a ration that is long enough to make a cow chew. Chewing produces saliva, saliva carries buffer into the rumen, and long particles form the mat that holds feed back for digestion.

It is estimated from the fibre content of the ration and the share of particles retained on the sieves of a particle separator. Rations that are chopped or mixed too fine can meet a fibre specification on paper and still leave cows short of effective fibre.

Written for the 2026 edition of the library.