Never drop the digestibility clock
NDFD30 and NDFD48 are different measurements because the microbes had different amounts of time.
4 min read · 2026-09-17
Fiber disappearance increases with incubation time. Reporting only “NDFD 52” removes the information needed to interpret or compare the value. The same problem applies to uNDF time points. Thirty hours and forty-eight hours are not two spellings of one test.
Laboratory keys and NASEM both require the method and the clock. Keep the incubation time, laboratory, and basis attached to the result. The useful habit is to compare NDFD30 with NDFD30 — not with NDFD48 because the numbers happen to share a name.
Check in the barn
What to check: Is the time point printed next to NDFD and uNDF? Are you trending one laboratory and one method, or mixing NIR and wet chemistry across weeks? If a number arrived without its clock, it is incomplete — ask for the time point before you rank the forage.
Sister notes on this universe cover same-ndf-different-forage and a-number-without-a-unit-is-not-a-result. The physically-effective-fiber universe’s particle-size-holds-the-mat note reminds you that a digestibility clock still does not measure the particle the cow chewed. Educational only — not a diagnosis, prescription, or ration formula.
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The same NDF can describe a different forage
NDF gives cell-wall amount; digestibility, lignin, uNDF, rate, and particle form determine how that wall behaves.
Sister note · 4 min
Home plate: Rumen · Reading fiber fractions · NDF digestibility
- NDF digestibilityDisappearance by timePlaced here
- A number without a unit is not a resultPercent, ppm, mg/kg, Mcal/lb, and Mcal/kg can turn the same digits into very different decisions.Sister note
- Chemical fiber is not effective fiberGrinding can leave the NDF percentage intact while removing much of the particle structure that stimulates chewing.Sister note
Mark size is the kind. Color is the atlas area.
- Focus
- Field note
- Rumen
Sources
- Understanding and Significance of Forage Results — Dairy One Forage Laboratory
- Nutrient Requirements of Dairy Cattle, 8th revised edition — NASEM (2021)
- In Vivo Digestibility of Forages — Penn State Extension