Applied · 11 min · Topic universe
Physically effective fiber
Particle size is what makes a high-energy diet still chew. Learn the sieves, the mat, and the ration the cow actually eats.
The system
Four-compartment stomach · educational plate
Field notes
Short articles on this topic
Two to four minutes. The weekly unit an agent can add without rebuilding the system.
3 min · 2026-09-07
Shake the bunk, not the memory
The particle box is only honest if the sample is the diet the cow can reach.
Read the note3 min · 2026-09-07
The top sieve is not the goal
Long stems look like fiber and often become refusals.
Read the note
The numbers
Benchmarks, not a ration
Ranges from extension and textbooks. Use them to read the cow, not to write a formula.
TMR on the 19 mm sieve
2–8%
Alarm: A heap of stems cows will not eat
Penn State’s high-producing TMR guide. More is not better if cows sort.
Penn State Particle Separator — Penn State ExtensionTMR classified physically effective
60–70%
Share retained on the top three sieves. Multiply by NDF only after you judge grain sitting on the 4 mm screen.
Penn State Particle Separator — Penn State ExtensionTMR in the bottom pan
≤30–40%
Alarm: A pan that looks like meal
Too much pan usually means the mat will not hold. Confirm with chewing and manure, not the box alone.
Penn State Particle Separator — Penn State Extension
Spot it
What you see · what it means · what to check
Check yourself
Five questions from this universe
1 of 5
What does physically effective fiber do that NDF on paper may not?
Sources
- Penn State Particle Separator — Penn State Extension
- Methods Used to Measure Forage and Ration Particle Size — Penn State Extension
- From Feed to Milk: Understanding Rumen Function — Penn State Extension
Stomach figure adapted from the public-domain 1905 plate Interior of a cow (The Household Physician; Wikimedia Commons) and standard ruminant-stomach teaching figures. Educational only.
Not a veterinary diagnosis, prescription, or ration formula.