Forage Quality: How Is It Defined and Measured?

Edward Twidwell, Han, Kun-Jun

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Ed Twidwell and Kun-Jun Han

Forages, the key element in grassland agriculture, are plants such as grasses and legumes used in livestock production and soil conservation. Forages are edible plants grown for livestock feed, land conservation and reclamation and other uses. Forage crops are an important component of Louisiana agriculture, as about 2 million acres are devoted to pastureland, and about 370,000 acres are devoted to hay production. In addition to the productivity of various forage crops, livestock producers are also interested in determining the nutritive value of these crops. Estimating the nutritive value, or forage quality, of these crops is somewhat difficult. Forage quality is defined in various ways, but it is often poorly understood. It is a simple concept that encompasses much complexity, and it often receives far less consideration than it deserves. Forage quality can be defined as the potential of forage to produce a desired animal performance. It includes the acceptability of the forage, its chemical composition and the digestibility of the nutrients. In practical terms, it has been referred to as “animal weight gain” or “milk in the bucket.”

There are many factors that influence forage quality. Maturity stage at harvest is the most important factor. As plants mature and become more fibrous, forage intake and digestibility decrease. Another factor is the leaf-to-stem ratio of the plants harvested. The relative amount of leaves to stems is important as leaves contain higher levels of nonstructural carbohydrates and protein than stems. Thus, forages with a greater amount of leaves are more likely to be of higher quality. Finally, environmental conditions such as temperature and humidity can affect forage quality. As temperatures rise during the summer months, larger amounts of cell wall material are deposited within the plant, causing the forage quality to decline. Rain can have a dramatic negative impact on forage quality. Rain can remove high quality soluble nutrients within the plant, which reduces the forage quality of the harvested crop. Rain can also cause the harvested crop to develop mold, which also reduces the feeding value of the forage.

When attempting to measure forage quality, there are two major methods used: visual appraisal and chemical analysis. Visual appraisal is the oldest and most common method of determining forage quality. This method involves evaluating the forage by examining the color, odor, leafiness, maturity and presence of foreign material, such as weeds (Figure 1). Although this method is quick and inexpensive, it is a subjective method, and results typically vary substantially from person to person. Chemical analysis is the most accurate method to assess forage quality. This method involves taking a representative sample of the forage and sending it to a forage laboratory for analysis. A hay probe should be used to collect the sample (Figure 2). Samples should be taken from a minimum of 10 hay bales, and these cored samples should be mixed in a 1-quart plastic bag and sent to a laboratory for analysis.

The desirable forage sample amount of about 10 ounces is enough for forage analysis. Once samples are delivered to the LSU AgCenter Forage Quality Lab on the LSU campus in Baton Rouge, all samples are re-dried in a drying oven to standardize the moisture content. The drying time differs depending on the sample conditions. The dried forage will be ground using specialized mills to a 1-millimeter particle size. Finally, samples are ready for the necessary chemical analyses or nondestructive analyses, depending upon the client’s request. Currently, general forage quality analysis is conducted using near infrared reflectance spectroscopy, a nondestructive method that is rapid and more economical than destructive methods, such as wet chemistry.

The LSU AgCenter collaborates with a national forage and feed testing consortium to use the consortium’s forage quality analysis protocols. The “routine analysis” option will fit the nutrient value analysis demands of most forage and livestock producers for an economical service fee of $15 per sample. This analysis provides nutrient value information, such as dry matter, crude protein, energy, macro minerals, sugar and a relative forage quality index. Also, conventional wet chemistry analysis is available at the laboratory for nonconventional feed samples or research samples for specific analysis purposes. Forage test results will be returned to the client within seven to 10 days upon receipt. Sample submission forms and other information about the testing can be found at the AgCenter Forage Quality Lab website:

Forage test results can be used in several applications. Producers can use the test results to aid them in formulating livestock rations. By knowing the exact chemical composition of the forages used, producers can supplement these forages with the correct amount of energy or protein supplements to form a balanced ration. Producers can also use forage test results to help them market their hay. This practice aids the seller in pricing hay and provides valuable information to the buyer about how to use a forage most effectively in a livestock feeding program. Finally, producers can use the test results to aid them in making changes to their forage management operation, such as cutting their hay at an earlier maturity stage or perhaps storing their hay in a barn.

Ed Twidwell is a professor, and Kun-Jun Han is an associate professor, both in the LSU School of Plant, Environmental and Soil Sciences.

This article appeared in the fall 2022 issue of Louisiana Agriculture.

A man smells a handful of hay.

Figure 1A: Smelling hay can help determine forage quality. Photo by Kyle Peveto

A man feels of a handful of hay.

Figure 1B: Visual appraisal, the most common method of determining forage quality involves evaluating the forage by examining the color, odor, leafiness and maturity as well as the presence of foreign material, such as weeds. Photo by Kyle Peveto

A man puts a sensor into a square bale of hay.

Figure 2: A hay probe can be used to collect samples of forage. LSU AgCenter photo.

12/15/2022 9:57:42 PM
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