Milk Urea Nitrogen & Read Your Feeding Balance
Diagnoses protein vs energy
Read your herd's bulk-tank MUN against milk-protein % to see whether protein is over- or under-fed. Target MUN is 10–14 mg/dL — high means excess degradable protein or short energy; low means a protein deficit.
Enter your herd milk test
Next: Reduce dietary CP/RDP 1–2 points to cut wasted N and feed cost; recheck MUN.
MUN target ≈ 10–14 mg/dL; milk protein ≈ 3.0–3.4%. High MUN = excess rumen-degradable protein vs energy; low MUN = protein deficit. Wasted urinary N ≈ 12.54 × (MUN above 14) g/cow/day (Jonker/Kohn/Erdman 1998), converted to feed CP × 6.25. Interpretation per Penn State / Wisconsin dairy extension. Bulk-tank planning estimate.
MUN — key facts
- Target MUN
- 10–14 mg/dL
- Target milk protein
- 3.0–3.4%
- High MUN
- excess RDP / short energy
- Low MUN
- protein deficit
- Urinary N
- ≈ 12.54 g/cow per mg/dL MUN
- Wasted N basis
- MUN above 14 mg/dL
- MUN ≈ BUN
- milk proxy for blood urea
- Privacy
- Runs in your browser; nothing uploaded
MUN × milk-protein feeding-diagnosis grid
The classic dairy interpretation grid. Find your MUN band down the side and your milk-protein band across the top.
| MUN \ Milk protein | Low (< 3.0%) | OK (3.0–3.4%) | High (> 3.4%) |
|---|---|---|---|
| High (> 14) | Excess RDP + energy shortfall | Protein over-fed | High protein, high energy |
| Target (10–14) | Energy-limited milk protein | Well balanced | Balanced, strong protein |
| Low (< 10) | Protein deficit | Mild RDP shortfall | Efficient N use |
Source: Penn State / Univ. of Wisconsin / Virginia Tech dairy extension MUN interpretation guides.
A free milk test that tells you how to feed
Milk urea nitrogen comes on every routine milk test, and it is one of the cheapest diagnostics in dairy nutrition. It reflects the balance between rumen-degradable protein and fermentable energy: when the rumen has more degradable protein than it can capture as microbial protein, the surplus nitrogen becomes urea and shows up as a high MUN. Read alongside milk protein %, MUN separates a protein problem from an energy problem.
This tool plots your herd into the four-quadrant feeding-diagnosis chart, names the imbalance, gives the specific ration fix, and — when MUN is above target — puts a daily dollar figure on the protein you are buying and excreting. Use it on every test day to keep the ration in the efficient window. Pair it with the RDP/RUP Protein Balance and Dairy Cow Energy Balance tools for a complete feeding review.
How to use it — 5 steps
- 1Get the values. Take the bulk-tank or DHI MUN and the milk-protein percent.
- 2Enter them. Type MUN, milk protein, herd size and your protein-feed cost.
- 3Read the quadrant. See which feeding-diagnosis quadrant the herd lands in.
- 4Apply the fix. Follow the ration adjustment captioned for that quadrant.
- 5Re-test. Re-check MUN next test day to confirm it moved into the 10–14 window.
Frequently Asked Questions
What is a good MUN level for dairy cows?+
The widely used target window is about 10–14 mg/dL, read together with a milk-protein percent of roughly 3.0–3.4%. Within that box the ration's rumen-degradable protein and fermentable energy are in balance. Values outside it point to a specific imbalance — high MUN to excess protein or short energy, low MUN to a protein deficit.
What does a high MUN mean?+
A MUN above ~14 mg/dL usually means the rumen is receiving more degradable protein (RDP) than its fermentable energy can capture, so the surplus nitrogen is converted to urea and excreted. If milk protein is also low it points to an energy (starch) shortfall as well. The fix is to trim soluble/RDP protein and/or add fermentable energy, then re-test.
What does a low MUN mean?+
A MUN below ~10 mg/dL generally signals a protein deficit — not enough rumen-degradable protein to feed the microbes for peak microbial-protein yield. If milk protein is also low, the whole ration is short of protein. Adding degradable protein (e.g. soybean or canola meal, or a measured amount of urea) typically lifts both MUN and milk yield.
How do you read MUN against milk protein?+
Plot MUN on one axis and milk protein on the other to land in one of four quadrants. High MUN with low protein is excess RDP plus an energy shortfall; high MUN with adequate protein is simply protein over-fed; low MUN with low protein is a protein deficit; and on-target MUN with good protein is well balanced. The calculator places your herd and captions the quadrant with its fix.
How much money does high MUN waste?+
Every mg/dL of MUN above the upper target is protein the cow was fed and then excreted. Urinary nitrogen rises about 12.54 g per cow per day for each mg/dL of MUN (Jonker, Kohn & Erdman 1998); converted back to dietary crude protein that is roughly 0.08 kg of CP per cow per day per excess mg/dL. Multiply by herd size and your protein-feed cost to see the daily waste.
Is high MUN bad for the cow or the environment?+
Both. Producing and excreting excess urea costs the cow energy and has been associated with poorer reproduction at very high levels, and the excreted nitrogen loads slurry and increases ammonia and nitrate emissions. Trimming MUN back into the target window saves feed money and reduces the farm's nitrogen footprint at the same time.
Can MUN be too low and still be fine?+
Sometimes. A low MUN with high milk protein indicates very efficient nitrogen capture — the cow is turning most of its dietary nitrogen into milk rather than urine. That is generally good, but you should still confirm that rumen-degradable protein is not so low that it caps microbial growth, feed intake or peak yield.
Does MUN change through the day or season?+
Yes. MUN rises after feeding and varies with sampling time, diet changes, heat stress and forage quality, so single readings can mislead. Use bulk-tank or DHI averages and look at the trend across test days rather than reacting to one figure. Sampling consistently (same time relative to feeding) makes the trend reliable.
What is the difference between MUN and BUN?+
MUN is milk urea nitrogen, measured in the milk; BUN is blood urea nitrogen, measured in plasma. They track each other closely because urea diffuses freely between blood and milk, so MUN is a convenient, non-invasive proxy for the cow's protein-energy balance that you get for free on every milk test.
How do I lower MUN without losing milk?+
Reduce the most soluble, rapidly degradable protein sources first and replace some with rumen-undegradable (bypass) protein or fermentable energy so microbial yield holds. Improving the synchrony of energy and protein release in the rumen — for example pairing degradable protein with starch — captures more nitrogen as microbial protein and lowers MUN while protecting milk yield.
Why is on-target MUN with good milk protein the goal?+
It means the rumen is fermenting protein and energy together efficiently: degradable protein is being captured as microbial protein rather than lost as urea, and there is enough energy and metabolizable protein to support milk-protein synthesis. That quadrant gives the best combination of milk output, feed efficiency and low nitrogen waste.
Does this work for any breed or ration?+
Yes — the MUN target window and the quadrant interpretation apply across breeds and forage systems, because they reflect rumen protein-energy balance rather than a specific feed. Enter your bulk-tank MUN and milk protein and the diagnosis holds; only the magnitude of the ration tweak changes with your particular feeds.