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Relative feed value (RFV) is widely accepted as one of the best single values to estimate alfalfa quality. The RFV index tends to be oriented toward dairy production, but it has application for forages used by other types of livestock.
The basis for the RFV index calculation is discussed in Crop File 6.01.057, "Relative Feed Value". RFV is most applicable to both hay and silage of legumes, cool season grasses, and grass/legume mixtures. The equation can be applied to other forages (like warm season grasses, small grains, or sorghum forages), but should not be interpreted in the same way.
Grasses and other forages have more fiber than alfalfa, resulting in a lower RFV ranking. That fiber often is more digestible than alfalfa fiber, but the actual fiber digestibility does not affect the RFV if the total fiber content is the same. Grass hay, for example, is frequently ranked lower than it should by the RFV index even when it is a high-quality forage.
RFV was initially developed to help rank the potential energy intake of different hays by lactating dairy cows and their potential for milk production. Energy intake does not have as much influence on performance by other types of animals, like beef cows. This makes RFV less useful for comparing the impact of forage sources on performance of non-dairy livestock.
When forages are fed to animals in limited quantities, such as supplements for cow-calf herds and dry cows, the importance of RFV changes. Forage intake is then limited by limiting the amount fed, so the NDF content of the forage becomes less important to overall performance.
RFV can be used to help producers accurately distinguish between higher and lower quality forages, then make decisions about the potential use of the forage. Lab analyses can be used to set up a forage inventory for a livestock operation. The RFV values can help classify various forages according to potential use for livestock other than lactating dairy cows.
For example, if price ratios are correct, then it may be the best to sell the best quality forage off-farm as a cash crop. Medium quality forages could remain on the farm and be used for heifers, for bred cows, or for backgrounding. Poor quality forages could be used for maintaining stock cows.
The poorest forages might even be best used as bedding, if the cost of supplementing is too high.
Relative feed value is an "index" value with no units, so forage prices cannot be directly correlated with the RFV value. Hay with an RFV of 150 is not necessarily twice as good as hay with an RFV of 75. Pricing decisions may need to be based on the value of production differences and the intended use of the forage.
The RFV calculation does not account for forage protein level. Protein content generally decreases as fiber content increases - but not always - so the protein content may need to be considered separately from RFV when pricing forages.
Generally, the less fibrous the forage, the higher the RFV. Higher RFV indicates a higher energy, less bulky forage, so animals will tend to consume more of it. The final pricing decision should also consider other factors, like moisture content, color, odor, heat damage, weed content, and hay package type (stacks, bales, etc.)
Final use of the forage is also important when pricing. For example, a buyer of backgrounding quality hay is not likely to pay a premium for dairy quality hay since it probably exceeds the hay quality specifications. The buyer may require higher quality only in the starter or grower rations for feedlot cattle. The following table lists a series of RFV ranges with some suggested livestock uses, typical laboratory analysis values, and forage descriptions that might represent each range.
Table 1 has suggestions for forage use based on RFV ranking. Table 2 shows quality guidelines that the USDA Agricultural Marketing Service established to report market prices for various types of alfalfa and grass hay. The market reports for various locations are available at https://www.ams.usda.gov/market-news/hay-reports.
¶ Table 1. Suggested Livestock Uses for Legume and Grass Forages Using RFV |
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| RFV | Suggested for use with: | Typical values* | Description of Typical Hay Quality | ||||
| ADF % | NDF % | NE-L, Mcal/lb | DDM % | DMI % | |||
| >150 | Prime dairy cows; fresh and high producers | < 31 | < 40 | > 0.68 | > 65 | > 3.0 | Legumes: pre-bloom or bud stage |
| 125 – 150 | Good dairy cows; young heifers Excellent for backgrounding | 31 – 35 | 40 – 46 | 0.64 – 0.66 | 62 – 65 | 2.6 – 3.0 | Legumes: early bloom (one-tenth to less than one- fourth of the plants in bloom) |
| 103 – 124 | Good beef cattle; older heifers Marginal quality for dairy cows | 36 – 40 | 47 – 53 | 0.58 – 0.62 | 58 – 61 | 2.3 – 2.5 | Legumes: mid-bloom (half the plants in bloom) Grass: vegetative stage Grass/legume mix: less than 20% to 30% grass |
| 87 – 102 | Maintenance of beef cows Maintenance of dry dairy cows | 41 – 42 | 54 – 60 | 0.54 – 0.56 | 56 – 57 | 2.0 – 2.2 | Legumes: full bloom (most of plants in bloom) Grass: early head stage Grass/legume mix: less than 30% to 40% grass |
| 75 – 86 | Poor quality: may require supplementing with higher quality energy feeds and maybe other nutrients | 43 – 45 | 61 – 65 | 0.50 – 0.52 | 53 – 55 | 1.8 – 1.9 | Legumes: full bloom Grass: head stage (seeds in milk to late dough) Grass/legume mix: less than 50% to 60% grass |
| < 75 | Very poor quality: will require supplementing with higher quality energy feeds and other nutrients | >45 | > 61 | < 0.50 | < 53 | <0.19 | Legumes: very mature plants, predominantly stems Grass: late head stage, predominantly stems |
*RFV = Relative Feed Value; ADF = Acid Detergent Fiber; NDF = Neutral Detergent Fiber; NE-L = Net Energy of Lactation; DDM = Digestible Dry Matter; DMI = Dry Matter Intake (as percent of body weight)
¶ 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 – 54.5 | 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 |
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. accessed 08Aug2022 https://extension.okstate.edu/fact-sheets/forage-quality-interpretations.html
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. http://openprairie.sdstate.edu/extension_extra/352