Why it's Important to Test Forages

Why it's Important to Test Forages

Know what you have on hand before winter arrives.

As the season draws to a close, we often find we have made some good hay and some that was less good because of rain delay, less legume than expected or other reasons. We often do not test the lesser quality hay and simply feed it to heifers or other animals. This can be a big mistake! Knowing what is in the hay can make the difference between getting the animal performance expected or not and the need to buy supplement or not. Often individuals do not test hay assume certain needs and buy and feed supplements without knowing whether or not the supplements are really needed.

Check it out

The table below is an example of analysis of four alfalfa and grass hays. Note that clovers have about the same content of protein, fiber, energy and minerals at the same stage of maturity, so the samples could also be representative of clover/grass hays as well as the alfalfa/grass listed.



First look at the crude protein. Animal needs range from approximately 7% for mid-gestation mature dry cows to approximately 13% for beef cows nursing calves and higher for milking dairy cows. Sheep and horses generally need around vary from about 8% for idle, not lactating mature animals to 13 to 14% for growing and lactating animals. You can see that all samples, except 3 are adequate for non-lactating, idle adult animals and samples 1 and 4 are adequate for growing or lactating animals without additional protein supplement.

ADF is the old test to estimate energy. Now most forage testing laboratories can analyze for digestible fiber (NDFD) to better estimate energy of the forage. You can see that samples 2 and 4 have about the same ADF content but sample 2 has much higher digestible fiber and would result in better animal performance.

NDF is an estimate of the total fiber (neutral detergent fiber). The normal range is from 40% on early bloom legume hay to 72% on late cut grass hay. All cattle, sheep, horses and other ruminants need fiber. However too much fiber can limit the total feed intake and animal performance. If the NDF comes from grass it is more digestible than the NDF from legumes. Samples 1 and 4 would generally be adequate for growing animals with little additional supplement. Sample 2 is adequate for non-lactating, idle adult animals and animals fed sample 3 may need some additional concentrate, especially over winter.

It is also worthwhile to look at the mineral content of the forage. Phosphorus is often low in forage. Levels approaching 0.25 percent phosphorus on a DM basis are at the critical level. Samples 2 and 4 are low in phosphorus. Lactating cows and growing animals have higher phosphorus requirements. Thus animals fed hay from samples 1 and 3 need little additional phosphorus supplement (except for milking dairy cows) while animals fed sample 2 and 4 should receive additional phosphorus

Potassium levels of 0.6 to 0.8percent of the ration dry matter is considered adequate for growing dairy animals, beef cattle and sheep. Thus all forages have adequate potassium for animals and no further potassium supplement would be recommended. However, 2% and 3% potassium on a dry matter basis is the maximum tolerable concentration for sheep and beef cattle, respectively. So forage from sample 1 should not be fed to these animals. Sample 1 is acceptable for milking dairy cows.

The calcium level in sample 1 is high, indicating a high level of legume in the hay, while the other three samples are likely primarily grass. Lactating cows and growing calves will have the highest requirements needing approximately 0.39% and 0.45% calcium, respectively. All samples except 3 meet these requirements.

Magnesium requirements are generally met by the forages.

One can see that individual hays would need differing supplements depending on the category of animals being fed. Some hays could be more cost effectively being fed to certain animal types. The only way to know what is needed or to be able to most effectively use the hay is to test the forage and determine what is present.

Undersander is a University of Wisconsin-Madison Extension and research forage agronomist.

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