Chop length is not peNDF

Chop length on the harvester is a useful target, not the fiber story itself. On farm, peNDF is commonly estimated as the fraction of as-fed particles retained on the ≥4 mm Penn State Particle Separator screens, multiplied by NDF — and the number that matters is the diet the cow actually ate, not the ticket. Theoretical length describes what left the cutterhead. Delivered peNDF describes the physical effectiveness of particles after moisture, mixing, bunk push-ups, and sorting.

Kernel processing is a grain-starch story. It can change how fast starch ferments, but it is not the main way peNDF disappears from the bunk. peNDF usually leaks when overmixing grinds forage structure into fines, when dry fluffy hay floats out of a wet TMR, or when cows sort toward the pan. Prefer an as-fed TMR shake over arguing soft versus rigid stems on paper: shake fresh feed and refusals with the same separator and compare the distributions.

Check delivery, then the refusals, then walk the bunk after the first meal — not a locked two-hour stopwatch. If chop targets look right but cows sort or chew less, fix dry matter, load order, moisture, and mix time before you rewrite peNDF on paper. Overmixing is a common thief of structure; under-mixing leaves clumps that invite sorting.