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Color and protein are historically the two most common criteria used to evaluate hay quality, but they have limits. Green, high protein hay is usually of good quality, but actual performance of two hay lots that appear identical may be quite different.
Relative feed value (RFV) is an index developed by the Hay
Marketing Task Force of the American Forage and Grassland Council. It provides an objective way of ranking forages according to their relative nutritional value and quality.
An RFV ranking is based on the voluntary intake of the forage dry matter. This is calculated from predicted values of digestible dry matter (DDM) and dry matter intake (DMI). These two values are calculated from lab analysis results of acid detergent fiber (ADF) and neutral detergent fiber (NDF).
DDM and DMI provide an estimate of: 1) how much of the forage will be consumed, and 2) how much of the consumed forage will be digested. Neither protein nor color alone can accurately predict these two values.
The forage component called "fiber" contains the less digestible portions and is also responsible for "bulkiness". Fiber analysis provides a more accurate prediction of voluntary intake. The fiber content is usually lowest in leaves, highest in stems. ADF and NDF are the two forage fiber fractions used to determine DDM and DMI.
Forage ADF content is related to digestibility. Increased maturity, weathering, rain damage, and weeds can increase ADF content and decrease digestibility. DDM is an estimate of total digestibility of the feed and is calculated from ADF as follows:
The numerator (120) in the DMI calculation indicates maximum feed intake in alfalfa-based dairy rations when consumption is 1.2 lb of NDF per 100 lb of body weight.
RFV was developed for hay or haylage from cool season legumes, grasses, or legume/grass mixtures. It is not considered equally valid for corn silage or other forages.
RFV has no units and is calculated as follows:
• RFV = [(DDM% x DMI%) ÷ 1.29]
It ranks forages relative to the digestible dry matter consumption of full bloom alfalfa, assuming an average of 41% ADF and 53% NDF.
The divisor (1.29) was chosen so that the RFV of this “average” alfalfa has a value of 100. Protein content is important, but is not included in the RFV calculation because protein is influenced by factors unrelated to those that affect RFV.
Forage prices cannot be directly calculated from the RFV value. For example. hay with an RFV of 150 is not necessarily twice as good as hay with an RFV of 75. The RFV value does allow individuals to distinguish between high-quality or low-quality forages.
Color, smell. moisture. weed content, and other factors should also be considered when pricing forages, especially if they are obvious problems.
Table 1 compares appearance, chemical analysis, and RFV for quality grades established by the American Forage and Grassland Council. Tables 2 and 3 show quality guidelines that the USDA Agricultural Marketing Service established to report market prices for various types of alfalfa and grass hay. The market reports are available at ams.usda.gov/market-news/hay-reports.
¶ Table 1. Quality Grades for Legume and Grass Forages (1972, AFGC) |
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| Grade | RFV | Hay Type and Description | % CP | % ADF | % NDF | NEL |
| Prime | Leafy, green | |||||
| > 150 | Legume – prebloom or bud stage | >19 | < 30 | < 39 | > 0.68 | |
| 1 | Leafy, green | |||||
| 125 – 150 | Legume - early bloom (one-tenth to one fourth of plant in bloom) |
17 - 19 | 31 - 35 | 40 – 46 | 0.64 | |
| 105 - 110 | Grass - vegetative | 16 - 18 | 30 - 33 | 45 - 55 | 0.73 | |
| 115 – 137 | Grass/legume mix - less than 20% grass | 17 – 19 | 31 – 35 | 44 – 50 | 0.64 | |
| 2 | Leafy, light-green to green | |||||
| 101 – 120 | Legume - midbloom (half the plant in bloom) | 14 – 16 | 36 – 40 | 47 – 53 | 0.59 | |
| 92 – 107 | Grass - early head stage | 13 – 18 | 33 – 38 | 55 – 60 | 0.68 | |
| 98 – 113 | Grass/legume mix - less than 30% grass | 14 – 16 | 36 – 40 | 50 – 55 | 0.59 | |
| 3 | Stemmy, light-green to yellow-green | |||||
| 87 – 101 | Legume - full bloom (most plants in bloom) | 11 – 13 | 40 – 42 | 53 – 60 | 0.55 | |
| 82 – 89 | Grass - head (milk to dough) | 10 – 12 | 39 – 41 | 61 – 65 | 0.55 | |
| 85 – 99 | Grass/legume mix - less than 40% grass | 10 – 12 | 39 – 41 | 55 – 62 | 0.55 | |
| 4 | Predominantly stems, brown to green | |||||
| 77 – 84 | Legume - full bloom (all plants in bloom) | 8 - 10 | 43 – 45 | 61 – 65 | 0.55 | |
| 77 – 84 | Grass - head (late dough stage) | 8 – 10 | 43 – 45 | 61 – 65 | 0.5 | |
| 77 – 84 | Grass legume mix - less than 50% grass | 8 – 10 | 43 – 45 | 61 – 65 | 0.5 | |
| Fair | Predominantly stems, brown to green | |||||
| < 77 | Mostly grass in late head | < 8 | > 45 | > 65 | < 0.45 | |
¶ Table 2. USDA Hay Quality Designation Guidelines |
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| Quality designation | Alfalfa (domestic livestock use and not more than 10% grass) | Grass hay | |||||
| RFV | ADF % | NDF % | TDN %, 100% DM | TDN %, 90% DM | Crude protein % | Crude protein % | |
| Supreme | > 185 | < 27 | < 34 | > 62 | > 55.9 | > 22 | --- |
| Premium | 170 – 185 | 27 – 29 | 34 – 36 | 60.5 – 62 | 54.5 – 55.9 | 20 – 22 | > 13 |
| Good | 150 – 170 | 29 – 32 | 36 – 40 | 58 – 60 | 52.5 – 55.9 | 18 – 20 | 9 – 13 |
| Fair | 130 - 150 | 32 – 35 | 40 – 44 | 56 – 58 | 50.5 – 52.5 | 16 – 18 | 5 – 9 |
| Utility | < 130 | > 35 | > 44 | < 56 | < 50.5 | < 16 | < 5 |
¶ Table 3. Visual and Sensory Criteria Typically Used to Designate Hay Quality |
|
| Supreme | Very early maturity (pre-bloom), soft fine-stemmed, extra leafy. Excellent green color and no damage. |
| Premium | Early maturity - pre-bloom in legumes or pre-head in grasses; extra leafy and fine-stemmed. Green and free of damage. |
| Good | Early to average maturity - early to mid-bloom in legumes or early headed grasses. Leafy, fine to medium-stemmed. Free of damage other than slight discoloration. |
| Fair | Late maturity- mid to late-bloom in legumes or headed grasses; moderate or less in leaf content, generally coarse-stemmed, with slight damage. |
| Utility | Very late maturity such as mature seed pods in legumes or mature grass heads; coarse stems. This category may include hay discounted due to excessive damage, mold or weed content. (Defects will be identified in the market report for this category). |
Moore & Undersander. 2002. Relative Forage Quality: An Alternative to Relative Feed Value and Quality Index. Proc. of 13th Annual Florida Ruminant Nutrition Symposium. pp 16-32.
Undersander, Mertens, & Thiex. 1993. Appendix A1: Relative Feed Value Index in Forage Analysis Procedures. National Forage Testing Association. pp. 112-113.
Redfearn & Zhang. 2017. Pub. No. PSS-2117, Forage Quality Interpretations Oklahoma State Coop. Ext. Serv. 4 pg.
Jeranyama & Garcia. 2004. Understanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ), Extension Extra. Paper 352. South Dakota State Univ. Coop Ext., Brookings SD. 3 pg
USDA. Hay Quality Designation Guidelines. Livestock, Poultry, and Grain Market News, Agricultural Marketing Service. accessed 08Aug2022