Water is a fiber plasticizer
Forage dry matter changes how the TMR mixes and how the particle box reads — even when chop length matches a drier day.
Knowledge level in this topic: Advanced. Mechanism and stacked risk in this topic — assumes the first-pass frame.
3 min read · 2026-09-10
When we talk peNDF we often fixate on chop length. Moisture changes what happens next. peNDF is still estimated from particle size × NDF on the diet the cow ate — usually particles retained on the ≥4 mm Penn State screens times NDF. Dry matter does not rewrite that definition, but it changes mixing behavior and how the separator reads an as-fed sample.
Wet forage tends to tear and smear under augers more readily than a drier crop at the same theoretical chop. What looked adequate at the cutterhead can arrive at the bunk finer after over-aggressive mix time. A PSPS shake on fresh TMR is the check: if forage DM drops, re-shake after mixing, not only at harvest. Compare as-fed and refusals the same way.
Moisture can also change bunk behavior. Wetter mixes may hold fines better against sorting; overly dry fluffy long hay can float and invite selection. Those are operational delivery claims — watch the bunk face and the refusal map — not a claim that water "collapses the mat" by plasticizing cell walls into mush.
When forage dry matter drops, re-check particle size after mixing, watch bunk sorting and rumination, and treat mix aggressiveness as a peNDF lever before rewriting fiber on paper.
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Chop length is not peNDF
Chop length is a harvester setting; peNDF is the fiber structure that actually reaches the rumen after moisture, processing, mixing, and sorting.
Knowledge level in this topic: Advanced. Mechanism and stacked risk in this topic — assumes the first-pass frame.Sister note · 3 min
Home plate: Rumen · Physically effective fiber · Particle size
- Particle sizeWhat actually stimulatesPlaced here
- Refusals read the peNDF storyShake fresh TMR and the refusal pile with the same particle separator — divergence shows whether formulated peNDF actually reached the cow.Sister note
- Dry Matter and As Fed Are Different JobsScales weigh feed with its water, rations are balanced on dry matter, and a wetter or drier silage means the same scale weight no longer delivers the same dry matter.Sister note
Mark size is the kind. Color is the atlas area.
- Focus
- Field note
- Rumen
Sources
- Penn State Particle Separator — Penn State Extension
- Methods Used to Measure Forage and Ration Particle Size — Penn State Extension
- TMR Management – Ensuring Formulated Rations Make it to the Bunk — Penn State Extension
- Total Mixed Rations for Dairy Cows — Penn State Extension