AtlasRumenFIG. 01Foundation12 min
Inside the rumen
A dairy cow is a microbial fermentation system. Open the vat: four compartments, a stratified rumen, chewing, acids, and what leaves downstream.
ShareInside the rumen
Numbers
| Measure | Value | Spread · alarm | Why it matters |
|---|---|---|---|
| Rumen share of stomach capacityMerck Veterinary Manual | ~80% | The rumen is the fermentation vat. The reticulum, omasum, and abomasum are smaller and do different jobs. Teach capacity from this split, not from four equal bags. |
Quick check
Q 01 / 01
Which compartment is the true glandular stomach?
Field notes on this sheet
- Note 01Air at the face spoils the packDense packing and oxygen-barrier cover lock fermentation in. A ragged, slow face lets air back in and burns dry matter at the bunk.3 min · 2026-09-09
- Note 02Read manure before you rewrite the ticketThe alley is a daily report card on the ration the cow actually ate and fermented — consistency, fiber, and grain tell you before the mixer does.3 min · 2026-09-09
- Note 03The sensor is a barn alarm, not a diagnosisRumination and activity collars flag deviations from a cow’s own baseline — useful alarms that still need the cow, bunk, and stall before you act.3 min · 2026-09-09
Sources
- From Feed to Milk: Understanding Rumen Function — Penn State Extension
- Ruminant Digestive System — Merck Veterinary Manual
- Nutrient Requirements of Dairy Cattle, 8th revised edition — National Academies (NASEM, 2021)
- RUMINANT NUTRITION SYMPOSIUM: Role of fermentation acid absorption in the regulation of ruminal pH — Aschenbach et al. 2011, Journal of Animal Science
Plate credit
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.