Quick answer: A hay (forage) test reports a handful of numbers that tell you how much animals will eat and how much nutrition they will get. The ones that matter most: crude protein (CP) — total protein; ADF — fiber that drives digestibility (lower is better); NDF — total fiber that drives intake (lower means animals eat more); and TDN — an energy estimate. The two index scores, RFV and RFQ, roll those into a single grade where dairy-quality alfalfa runs 150–185+. Counterintuitively, protein barely affects RFV/RFQ — those indexes are built from fiber (ADF and NDF), not CP. Good dairy alfalfa tests roughly CP 20%+, ADF under 30%, NDF under 40%; good grass hay runs about CP 12%+, ADF under 35%, NDF under 50%. The catch: the numbers are only as honest as your sample — core about 20 bales per lot with a hay probe.
If you sell hay or buy it, sooner or later someone hands you a lab report full of acronyms — CP, ADF, NDF, TDN, NDFD, RFV, RFQ — and the numbers only help if you can read them. Plenty of producers never bother. As one grower put it after a buyer rejected a third of his alfalfa over a moisture probe, the common complaint on the forums is that people "didn't bother with testing because no one could interpret the results" (HayTalk). This guide fixes that. It is written for hay producers and buyers who want to turn a forage analysis into real feeding and pricing decisions — not a nutrition lecture.
We will walk every number on a standard report, explain what "good" looks like for alfalfa and grass, clear up the single most common misunderstanding (why high protein does not guarantee a high RFV), and show you how to pull a sample that actually represents your hay. The science here is drawn from Penn State Extension and the National Forage Testing Association, cross-checked against real producer experience on the hay forums.
Why test at all? The ~$15 that pays for itself
A forage test is the cheapest agronomic decision you will make all year. Penn State Extension notes that a lab analysis "usually costs less than $15.00 per sample," while guessing at quality quietly costs far more. In their dairy example, underestimating forage protein by a couple of points pushed feed costs up about $0.09 per cow per day — roughly $9.00 a day for a 100-cow herd, paying back the test in about three days.
For hay sellers the math is just as direct. At Pennsylvania hay auctions, each one-point increase in crude protein historically brought about $8.00 more per ton (a 1990–91 auction study — directional, not a current price). Sell 20%-protein hay as "18%" because you never tested, and you give that premium away on every load. A test lets you prove quality with numbers instead of asking a buyer to take your word.
The core numbers: CP, ADF, NDF, TDN, NDFD
Most of a standard report comes down to five values. Here is what each one means in plain terms:
- Crude Protein (CP) — total protein, on a dry-matter basis. Drives growth, milk, and gain. Higher is generally better, and it is the number most buyers ask about first.
- ADF (Acid Detergent Fiber) — the cellulose-and-lignin fraction. It tracks digestibility: the higher the ADF, the more mature and stemmy the hay, and the less of it the animal can actually digest. Lower is better.
- NDF (Neutral Detergent Fiber) — total fiber (cellulose, hemicellulose, lignin). It tracks intake: high-NDF hay is bulky and fills an animal up before it gets enough nutrition, so animals eat less of it. Lower means higher intake.
- TDN (Total Digestible Nutrients) — an estimate of usable energy, expressed as a percent. Higher TDN means more energy per pound.
- NDFD (NDF Digestibility) — the share of the fiber that is actually digestible, usually measured at 30 or 48 hours. A newer, more useful number, especially for grasses and dairy rations — higher is better.
The pattern to remember: CP and TDN you want high; ADF and NDF you want low. Maturity at cutting moves all four at once — let hay get stemmy and protein and energy fall while fiber climbs.
RFV vs RFQ: the two index scores
Because four numbers are awkward to compare bale-to-bale, the industry rolls them into a single index. There are two, and the difference matters.
Relative Feed Value (RFV) is the original. It combines just ADF and NDF into one score, calibrated so that full-bloom alfalfa lands at 100. The formula is:
RFV = [ (88.9 − 0.779 × ADF) × (120 ÷ NDF) ] ÷ 1.29
where 120 ÷ NDF estimates intake and 88.9 − 0.779 × ADF estimates digestibility (both on a %-of-dry-matter basis).
Relative Forage Quality (RFQ) is the newer, better index. It adds fiber digestibility (NDFD) and an energy (TDN) estimate, which makes it far more accurate for grasses and mixed stands that RFV tends to underrate. When both appear on a report and disagree, trust RFQ for grass and grass-legume hay.
Here is the part that trips up almost everyone: protein is not in either formula. A high-protein hay can still post a mediocre RFV if its fiber is high. A grower watching exactly that play out on pure alfalfa got the cleanest explanation on the forum:
"Protein really doesn't figure into RFV/RFQ, it is more about fiber digestibility. What are the ADF/NDF levels?"
In that thread the alfalfa tested 22.5% CP but only 132 RFV, because its ADF (33%) and NDF (44%) were higher than the lush look suggested. If your RFV seems low next to a strong protein number, the answer is always in the ADF and NDF — not the CP.
What "good" looks like (alfalfa and grass)
Numbers only mean something against a benchmark. These ranges line up with university-extension quality tables — use them as a yardstick, then match the grade to the animal:
| Measure | Excellent alfalfa | Excellent grass hay |
|---|---|---|
| Crude protein | 20%+ | 12%+ |
| ADF (lower = better) | under 30% | under 35% |
| NDF (lower = more intake) | under 40% | under 50% |
| TDN | 58–62%+ | 55%+ |
| RFV / RFQ | 150–185+ | 100–130+ |
Match the grade to the job. Supreme alfalfa at RFV 185+ earns its premium in a high-producing dairy ration; a dry beef cow on maintenance does fine on mid-range hay, and paying dairy money to feed it is waste. As a red flag, ADF above about 40% (alfalfa) or 45% (grass) means stemmy, low-digestibility hay, and CP under 8% on grass usually needs protein supplementation. The biggest single lever on every one of these numbers is cutting maturity — one bermudagrass producer tracking years of tests found "the biggest impact on crude protein percentage" was simply the number of days between cuttings (HayTalk).
How to take a sample that doesn't lie
A lab result is only as good as the handful of forage you send it. Grab-sampling a few flakes off one bale gives a number that means nothing. Penn State's protocol is the standard, and it is simple:
- Sample by lot. One lot = same field, same cutting, same conditions. Test each cutting and field separately — never blend them.
- Use a bale corer, not your hands. A hay probe pulls a uniform plug through many flakes; a grabbed "slice" over-samples leaf or stem and skews the result.
- Core about 20 bales per lot, inserting the probe to full depth into the end of round bales (or the end of square bales), choosing bales at random across the lot.
- Combine and seal. Mix the ~20 cores in a clean pail, fill one labeled, airtight plastic bag, and squeeze out the air. Keep it cool and ship promptly.
- Label completely — your name, the lot, forage type, cutting, and harvest date — so the lab's report ties back to the right hay.
For buying or selling, send the sample to a lab certified by the National Forage Testing Association so both sides trust the numbers. And test at the moisture you actually baled — a hay moisture tester at baling protects the quality you are about to measure.
Turning test numbers into a price
A test is also your best sales tool: it lets you advertise a specific RFV/RFQ and protein figure instead of "good clean hay." Quality-sensitive buyers — dairies and horse owners especially — will pay up for tested numbers, and the premium is well documented. We cover the full method in our guide to how to price hay, and how density and presentation factor in under net-wrap roll weight vs. quality. The short version: prove the quality with a test, then protect it from the baler to the buyer so the bale that arrives still matches the report.
Frequently asked questions
What is a good RFV for alfalfa hay?
For dairy-quality alfalfa, aim for an RFV of roughly 150 to 185 or higher; "supreme" hay tops 185. Mid-100s RFV is solid beef-cow hay, and anything near 100 is mature, lower-energy forage. Pair the RFV with crude protein and your animal's needs before deciding what it is worth.
What is the difference between RFV and RFQ?
RFV uses only ADF and NDF, so it works best for legumes like alfalfa. RFQ adds fiber digestibility (NDFD) and an energy estimate, making it more accurate for grasses and mixed stands. When a report shows both and they disagree, trust RFQ for grass or grass-legume hay.
Does high protein mean a high RFV?
No. Protein is not part of the RFV or RFQ formula at all — both are built from fiber (ADF and NDF). Hay can test high in crude protein yet post a mediocre RFV if its fiber is high. If your RFV looks low next to strong protein, check the ADF and NDF.
How many bales should I sample for a hay test?
Core about 20 bales per lot with a hay probe, sampling each field and cutting separately. Insert the probe to full depth into the end of the bale, mix the cores in a clean pail, and send one sealed, labeled bag. Twenty random cores capture the variation a few grab samples miss.
What is a good protein level for grass hay?
Quality cool-season grass hay generally tests 12% crude protein or higher; 10–12% is average and 8% or below is low and may need supplementing. Grass protein falls fast as the plant heads out, so cutting maturity matters more than species for the protein number.
The bottom line
Reading a hay test comes down to four working numbers — CP and TDN you want high, ADF and NDF you want low — plus an RFV or RFQ index that rolls the fiber side into one grade. Remember that protein lives outside those indexes, benchmark your results against the alfalfa and grass ranges above, and never trust a number that came from a careless sample. Do that and a $15 test stops being a mystery and starts setting your rations and your asking price.
Tested quality is only worth something if it survives storage and handling. A tight, full-width XES® bale net wrap holds leaf, color, and shape from the field to the buyer, so the bale they open still matches the report you sent — compare options in our best bale net wrap guide.
Sources: Penn State Extension, "Forage Quality Testing: Why, How, and Where" (extension.psu.edu, accessed June 21, 2026); National Forage Testing Association (foragetesting.org, accessed June 21, 2026); University of Kentucky Forage Extension, forage testing resources (uky.edu/Ag/Forage, accessed June 21, 2026); HayTalk.com forum threads "Hay Testing Results Interpretation" (#99734), "High CP low RFV 28 day alfalfa" (#92790), and "Hay Sample Results, 2008 — Coastal Bermuda in Texas" (#11558), accessed June 21, 2026. The $8/ton-per-protein-point and per-cow cost figures are dated extension examples (early 1990s), directional rather than current; verify against today's market data.
Featured photo: Alfalfa round bales in a Montana field by Gary D Robson, licensed under CC BY-SA 3.0, via Wikimedia Commons.
