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Laboratory Forage Analysis Issues

by Don Ball

The last issue of Cooperative Farming News contained an article that discussed laboratory analysis of forage. Laboratory analyses can be extremely useful, but having such analyses run does not necessarily eliminate all problems associated with assessment of forage quality. Examples of issues that sometimes arise include the following.

Sampling Bias

The biggest source of variation in laboratory analysis results is sampling. Laboratory personnel report that they receive everything from huge flakes of hay to small quantities of pulverized feed or forage in a bag or bottle. The proper way to sample hay is to use a hay probe and take at least 20 sub-samples from randomly chosen bales from a single lot (a "lot" is defined as hay from the same field and cut under uniform conditions within a 48-hour time period).

Failure To Accept Some Variation

People who are in the business of selling hay sometimes complain that a customer wants hay at a minimum specific level of energy or a maximum level of fiber and absolutely will not accept anything less. For example, a customer may have stated he wants no less than 56% total digestible nutrients (TDN) and would not accept hay containing 55.6% TDN.

While it is commendable to have high standards, it is important to remember that there is some variation in hay analysis results. For example, leaves are much better in quality than stems, so only a small difference in the amount of leaves versus stems in a sample can impact substantially on laboratory analysis results. Another example is that the presence of weeds in hay can likewise affect analysis results. Finally, there is even a bit of laboratory variation (i.e., there can be slight differences in results even when a test is run twice on identical material).

The point is that laboratory analyses are subject to some variation, especially due to differences in sampling technique, as discussed earlier. A laboratory analysis might be best viewed as a reliable indicator of the approximate forage quality of a lot of hay or other feed material.

Misunderstandings About Dry Matter

Some people apparently are confused about the practical implications of the percent dry matter in a forage sample, especially with regard to buying and selling hay. Dry matter is simply the part of a forage or feed other than water. The nutritive value of forage lies primarily in the energy, protein, and minerals it contains, because water is inexpensive and provided to animals separate from forage. Thus, although animal nutritionists may use "as fed" laboratory analysis values in calculating animal rations, the forage quality of various lots of hay should normally be compared on a dry matter basis.

The dry matter content of hay can be of importance, however. For example, a ton of hay that is 10% moisture actually contains about 200 more pounds of dry matter than a ton of hay that is 20% moisture. In addition, high moisture hay is more likely to contain mold and very low moisture hay of some forage species may not be eaten readily by animals, either of which may affect intake and animal performance.


Laboratory forage analysis can be a valuable tool for assessing forage quality. There is invariably some variation in results, but this can be minimized (mainly through careful sampling). While there are limitations to the value of such analyses, in conjunction with sensory evaluation they can be a valuable indicator of probable animal performance and thus provide an indication of the economic value of the hay or other feed material. For more information on forage quality and other forage topics see the website www.alabamaforages.com.

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Date Last Updated January, 2006