How to read a hay test, and why "good-looking hay" cost you $2,000 last year

Two round bales can look identical and differ by a third in feed value. In a year when hay is $20 to $30 higher than last year and a lot of it was cut late or rained on, buying or feeding on looks is expensive. A forage test costs $20 to $30 through most extension offices and commercial labs and takes a week. Here is how to read one.

Getting a sample worth testing

Use a hay probe, not a handful. Core 15 to 20 bales from the same lot (same field, same cutting), mix the cores in a bucket, and send a quart. Most county extension offices lend probes. A grab sample off the outside of one bale tells you about the weather, not the hay.

The numbers

Dry matter (DM) / moisture. Everything else on the test is reported "as fed" and "dry matter basis." Use the dry matter numbers to compare hays. Hay above 18 to 20 percent moisture in a round bale is a heating and mold risk.

Crude protein (CP). The headline number. A dry, mid-gestation beef cow needs about 7 to 8 percent CP on a dry matter basis. Late gestation, 8 to 9. Lactating, 10 to 12. Growing calves, 12 to 14. Grass hay in a drought year commonly tests 6 to 9; good alfalfa tests 16 to 20.

TDN (total digestible nutrients). Energy. A dry cow needs about 50 to 55 percent TDN; lactating, 58 to 62; growing calves, 65-plus. Mature, stemmy grass hay tests 48 to 52. Energy is the nutrient more likely to be short in drought hay than protein, and it is the one people forget.

ADF and NDF. Fiber. ADF (acid detergent fiber) predicts digestibility; higher is worse, and above 40 to 45 means old, coarse hay. NDF (neutral detergent fiber) predicts how much a cow can physically eat; above 65 and intake drops.

RFV / RFQ. Relative feed value and relative forage quality are indexes built from the fiber numbers, with 100 as full-bloom alfalfa. They are for comparing hays and pricing them, not for balancing rations. A grass hay at 90 RFV and one at 110 are different feeds.

Nitrates. Drought hay, especially sorghum-sudan, millet, and any annual grass that was fertilized and then stressed, can carry toxic nitrate. Ask for the test. Below 0.5 percent NO3 (5,000 ppm) is generally safe; above 1 percent is dangerous; between, dilute with clean feed. Nitrates do not go away in storage.

Using it

To buy hay. Ask for the test before you agree on price; a seller who will not test has told you something. Price on the numbers: a $180 hay at 9 percent CP and 56 TDN beats a $160 hay at 6 and 50 by a wide margin once you count the supplement you will not have to buy.

To match hay to cattle. Feed the best hay to the animals with the highest requirement: first-calf heifers, thin cows, weaned calves. The mature dry cows in a 5 can eat the 7 percent hay all winter and be fine.

To decide on supplement. If the hay is short on protein, a couple pounds of distillers or a 20 percent tub fixes it cheaply. If it is short on energy, that is corn, gluten, or soyhulls, and it is a different bill. If it is short on both, the cheapest fix may be better hay. You cannot know which until you test.

Most extension services have a free ration-balancing spreadsheet that takes the test numbers directly. An hour with one in October saves a lot of guessing in February.