Measuring forage quality

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Source: University of Minnesota Extension

Quick facts

  • Forage sampling is important to maximize forage utilization and animal performance.
  • Ideally forages should be sampled soon after harvest as well as prior to feeding.
  • Visual assessments should be used along with forage testing to evaluate forage quality.

Importance of testing forage quality

Testing forage quality is important whether you plan to keep the forage or sell it. Forage testing will help match the forage to animal requirements, improve ration efficiency and provide a better estimate of quality than visual assessment alone. Testing will also help sell unnecessary forages because potential buyers will have a better idea of quality.

Matching animal requirements

Forage quality should match an animal’s nutritional intake needs. Different classes of livestock have different nutritional requirements. Testing forage quality allows you to better match forage sources to animal requirements. Forage quality can also be used to determine which forages to produce or purchase. More expensive, high-quality forages may not be necessary depending on the class of livestock being fed.

Forage sales

Forage quality sampling is also helpful for forage sales. Testing forages allows you to compare your forage against other sources. Most hay auctions and sales require forage quality testing. Referencing local forage sales and their associated quality can help determine approximately what your forage is worth. Different producers value quality factors differently, and will most likely look at what their forage quality needs are when determining value. A fair price is easier to achieve when both parties involved know the forage quality.

Visual assessment

Visual assessments of hay quality are recommended in addition to a lab analysis. However, visual estimations are no replacement for a forage analysis. Visual assessments should consider factors such as stage of maturity, color, leafiness, foreign material, odor and overall condition.

Visual assessments are also very important to detect potential quality issues that may not show up on a forage quality test. However, visual assessments cannot place an actual value on forage quality factors that are important when feeding hay. The following list includes factors that influence the quality of forages:

  • Time of day harvested
  • Stage of maturity at harvest
  • Temperature, rainfall, and climate
  • Variety grown
  • Cutting schedule
  • Harvest techniques
  • Harvest equipment
  • Proper or improper storage
  • Nutrient management
  • Foreign materials
  • Weeds, insects, fungal pathogens, etc.

Improve ration efficiency

While a few of these factors will come up in a visual assessment, the degree of influence on important quality factors such as crude protein (CP) and neutral detergent fiber (NDF) will vary. Under or overestimation of these quality factors will lead to reduced animal production and efficiency. Testing forage quality allows adjustments to be made in feed rations, which increases feeding efficiency of the forage.

Quality designations

The following quality designations have been adopted by the USDA Agricultural Marketing Service. These values are used in hay auction reports as a way to create unique categories for hay that can be used consistently across the country.

Very early maturity, pre-bloom, soft fine stemmed, extra leafy. Factors indicative of very high nutritive content. Hay is excellent color and free of damage.

  • Acid detergent fiber: under 27
  • Neutral detergent fiber: under 34
  • Relative feed value: over 185
  • Total digestible nutrients-100%: over 62
  • Total digestible nutrients-90%: over 55.9
  • Crude protein: over 22

Early maturity, i.e., pre-bloom in legumes and pre-heading in grass hays, extra leafy and fine-stemmed factors indicative of a high nutritive content. Hay is green and free of damage.

  • Acid detergent fiber: 27-29
  • Neutral detergent fiber: 34-36
  • Relative feed value: 170-185
  • Total digestible nutrients-100%: 60.5-62
  • Total digestible nutrients-90%: 54.5-55.9
  • Crude protein: 20-22

Early to average maturity, i.e., early to mid-bloom in legumes and early-heading in grass hays, leafy, fine to medium stemmed, free of damage other than slight discoloration.

  • Acid detergent fiber: 29-32
  • Neutral detergent fiber: 36-40
  • Relative feed value: 150-170
  • Total digestible nutrients-100%: 58-60
  • Total digestible nutrients-90%: 52.5-54.5
  • Crude protein: 18-20

Late maturity, i.e., mid to late-bloom in legumes, heading in grass hays, moderate or low leaf content, and generally coarse stemmed. Hay may show light damage.

  • Acid detergent fiber: 32-35
  • Neutral detergent fiber: 40-44
  • Relative feed value: 130-150
  • Total digestible nutrients-100%: 56-58
  • Total digestible nutrients-90%: 50.5-52.5
  • Crude protein: 16-18

Hay in very late maturity, such as mature seed pods in legumes or mature head in grass hays, coarse stemmed. This category could include hay discounted due to excessive damage and heavy weed content or mold. Defects will be identified in market reports when using this category.

  • Acid detergent fiber: over 35
  • Neutral detergent fiber: over 44
  • Relative feed value: under 130
  • Total digestible nutrients-100%: under 56
  • Total digestible nutrients-90%: under 50.5
  • Crude protein: under 16

Forage quality factor definitions

In order to interpret your forage quality report properly, you must understand the different terms used and their meanings. There are many different quality factors that can be reported-all with unique importance. The factors reported can vary depending on which lab you submit your samples and the services they provide. There are also certain quality factors that do not change from lab to lab and the most common ones are listed below.

is an estimate of a feed’s protein content. Crude protein can also be estimated as 6.25 times the nitrogen content for forages, because protein is approximately 16% Nitrogen.

The portion of dry matter in forages made up of cellulose, hemicellulose, lignin and ash. NDF consists of both the indigestible and partially digestible fiber. There are separate tests that can estimate the partially digestible portion of NDF. Because this is the total fraction of fiber it is negatively correlated with feed intake.

The portion of dry matter in forages consisting of cellulose, lignin and silica. It is negatively correlated with digestibility.

The sum of crude protein, fat times 2.25, digestible NDF, and structural carbohydrates. The equations used to calculate TDN can vary by region and by nutritionist.

Relative Feed Value (RFV) versus Relative Feed Quality (RFQ)

Both Relative Feed Value and Relative Feed Quality are based around the same concept.

(Intake x Energy content)/Standard

The RFV and RFQ standard is set at 100 for full bloom alfalfa, and designed to have similar responses so they could be used interchangeably. However, there are differences in how they are calculated and how they may be used.

RFV is based on combining digestibility and intake potential, and is calculated from the ADF and NDF portions of the hay. This works well for alfalfa hay as legumes tend to have lower fractions of digestible NDF as compared to grass hay. This also means it is not as good of a predictor for grass hay quality due to increased digestible NDF in grasses.

RFQ incorporates TDN into the equation to better estimate quality. RFQ also incorporates the digestible portion of fiber into the calculations. While both RFQ and RFV should be very similar as it pertains to alfalfa hay quality, RFQ typically does a better job estimating quality for grass hay sources. They will also differ when a legume hay source’s digestible fiber portion is not average. In this situation RFQ should do a better job when estimating quality in that situation.

Nathan Drewitz, University of Minnesota Extension agriculture production systems educator and Jared Goplen, University of Minnesota Extension crops educator

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