Feed quality of alfalfa harvested as haylage or hay depends, to a great extent, on the maturity of the stand. With increasing maturity, plant structural carbohydrates, as measured by the ADF and NDF fractions, increase. These fiber fractions represent the more indigestible parts of the plant. As a result, digestibility and energy obtained through fermentation decrease with maturity. Relative feed value (RFV) has been used for years to compare the quality of legume and legume/grass hays and silages. Having one index to price hay and predict animal performance has been very useful for livestock producers and hay farmers

Garcia, Alvaro D.

Jeranyama, Peter

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South Dakota State UniversityOpen PRAIRIE: Open Public Research Access InstitutionalRepository and Information ExchangeExtension Extra SDSU Extension8-1-2004Understanding Relative Feed Value (RFV) andRelative Forage Quality (RFQ)Peter JeranyamaSouth Dakota State UniversityAlvaro D. GarciaSouth Dakota State UniversityFollow this and additional works at: http://openprairie.sdstate.edu/extension_extraThis Other is brought to you for free and open access by the SDSU Extension at Open PRAIRIE: Open Public Research Access InstitutionalRepository and Information Exchange. It has been accepted for inclusion in Extension Extra by an authorized administrator of Open PRAIRIE: OpenPublic Research Access Institutional Repository and Information Exchange. For more information, please contact michael.biondo@sdstate.edu.Recommended CitationJeranyama, Peter and Garcia, Alvaro D., "Understanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ)" (2004).Extension Extra. Paper 352.http://openprairie.sdstate.edu/extension_extra/352Feed quality of alfalfa harvested as haylage or haydepends, to a great extent, on the maturity of the stand.With increasing maturity, plant structural carbohydrates,as measured by the ADF and NDF fractions, increase.These fiber fractions represent the more indigestibleparts of the plant. As a result, digestibility and energyobtained through fermentation decrease with maturity. Relative feed value (RFV) has been used for years tocompare the quality of legume and legume/grass haysand silages. Having one index to price hay and predictanimal performance has been very useful for livestockproducers and hay farmers.Relative Feed Value (RFV)The Relative Feed Value index estimates digestibledry matter (DDM) of the alfalfa from ADF, and calcu-lates the DM intake potential (as a percent of bodyweight, BW) from NDF. The index is then calculated  asDDM multiplied by dry matter intake (DMI as a % ofBW) and divided by 1.29.  The index ranks forages relative to the digestibleDMI of full bloom alfalfa, assuming 41% ADF and 53%NDF. The RFV index is 100 at this growth stage.DDM = Digestible Dry Matter = 88.9 - (0.779 x % ADF) DMI = Dry Matter Intake (% of BW) = 120 / ( % NDF )RFV = (DDM x DMI) / 1.29where the numerator, 120, in the DMI calculation indi-cates maximum feed intake in alfalfa-based dairy rationswhen NDF is 1.2 lb per 100 lb of body weight; the divi-sor, 1.29 in the RFV calculation was chosen so that theRFV of full bloom alfalfa has a value of 100.Example:  Alfalfa hay or haylage with 32% ADF              and 40% NDF(Plug in values for ADF and NDF on a dry matter basis) DDM = 88.9 - (0.779 x 32) = 63.97 DMI = 120 / 40 = 3 RFV = (63.97 x 3) / 1.29 = 149 Relative Feed Value reflects both digestibility (from% ADF) and intake potential (from % NDF) of alfalfa. Limitations of the RFV method include:1. DDM and DMI are assumed constants for all forages. 2. ADF and NDF are the only laboratory values used in the calculation. 3. Crude protein concentration of forage is not used.4. RFV cannot be used in ration formulation or  evaluation. Forage quality parameters including RFV ranking foreach type of forage are in Table 1.Higher RFV values indicate higher forage quality.Since the RFV system was developed using legumeforages and intake responses of lactating dairy cows,it works best when applied to that situation.Relative Forage Quality (RFQ)Relative feed value is calculated by estimating thedigestibility of the forage dry matter, and how muchthe cow can eat based on its “filling” capacity. However,cows sometimes perform differently even when fedforages of identical RFV. Variations in the digestibilityof the NDF fraction can probably account for thesedifferences. 1ExEx8149August 2004COLLEGE OF AGRICULTURE & BIOLOGICAL SCIENCES / SOUTH DAKOTA STATE UNIVERSITY / USDAUnderstanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ)Peter Jeranyama, Plant Science Department, andAlvaro D. Garcia, Dairy Science Department Fiber from grass and legumes naturally differs indigestibility, as it also does when grown under differentambient temperatures. RFV of first-cutting alfalfa willbe similar to that of second and third cuttings harvestedat similar stages of maturity.  However, fiber fractiondigestibility from each cutting will be different, as thisis influenced by ambient temperatures at the time ofgrowth and development.  Therefore, differences infiber digestibility are not taken into account in the RFVcalculation and cows may perform differently when fedforages from different cuttings.Researchers at the University of Wisconsin havedesigned the relative forage quality (RFQ) index thatuses fiber digestibility to estimate intake as well as thetotal digestible nutrients (energy) of the forage. The RFQ index is an improvement over the RFVindex for those that buy and sell forages, and it betterreflects the performance that can be expected fromcattle fed those forages. One other advantage of the RFQ prediction is that itdifferentiates legumes from grasses. The higher neutral detergent fiber in grasses willmake RFQ a better predictor of quality than RFV. TheRFQ emphasizes fiber digestibility while RFV usesdigestible dry matter intake. Although grasses have higher fiber fractions (ADF and NDF), they also havelower lignin content (Table 2).  A comparison of data generated by the OlsonBiochemistry Laboratory, SDSU shows that RFQ isslightly higher than RFV for the same sample. A rela-tionship between RFV and RFQ has been derived fromthis limited data set and is presented in Figure 1.The RFV generally penalizes grasses because of thehigher fiber fraction compared with alfalfa. The RFQcredits grasses because the grass fiber tends to be moredigestible than alfalfa fiber. Table 2 shows higher cellwall digestibility for timothy than alfalfa when incubat-ed for 72 hr in rumen fluid-buffer solution.Relative Forage Quality CalculationIn the RFQ calculation total digestible nutrients(TDN) substitutes for DDM.  Intake and TDN arecalculated from fiber digestibility obtained in thelaboratory. For RFQ:RFQ = (DMI, % of BW) * (TDN, % of DM) / 1.23The value 1.23 ensures the equation has a mean andrange similar to that of RFV. Calculations to estimate TDN and DMI for alfalfa,clovers, and legume/grass mixes are as follows:For TDN:TDN = (NFC*.98) + (CP*.93) + (FA*.97*2.25) + (NDFn * (NDFD/100) – 7 Where: CP = crude protein (% of DM) EE = ether extract (% of DM) FA = fatty acids (% of DM) = ether extract - 1 NDF = neutral detergent fiber (% of DM)NDFCP = neutral detergent fiber crude proteinNDFn = nitrogen free NDF = NDF – NDFCP, else estimated as NDFn = NDF*.93NDFD = 48-hour in vitro NDF digestibility (% of NDF)NFC = non fibrous carbohydrate (% of DM) = 100 – (NDFn + CP + EE + ash).Table 1. Forage quality values of some forages at        different growth stages.Forage type CP        ADF        NDF        RFV%Alfalfa-prebud 22 28 38 164Alfalfa-bud 20 30 40 152Alfalfa-early bloom 18 33 43 138Alfalfa-full bloom 16 41 53 100Alfalfa-seed pod 14 43 56 92Alfalfa + grass 13 39 54 101Bromegrass, late vegetative 10 35 63 91Bromegrass-late bloom 7 49 81 58Corn silage-well eared 10 28 48 133Corn silage-few ears 8 30 83 115Sorghum silage 8 32 52 114Source: Dunham (1998)Table 2. Nutrient composition of selected forages.Cell       wall Forage type CP        NDF       ADF     Lignin  digestibility*%Alfalfa 16 49 34 7 46Corn silage 10 51 28 4 68Timothy 10 66 34 4 57* The % of NDF lost in 72 hr of incubation. Source: Collins (1988)For DMI:DMI = 120/NDF + (NDFD – 45) * .374 / 1350 * 100Where: DMI is expressed as % of body weight (BW) NDF as % of DMNDFD as % of NDF45 = average value for fiber digestibility of alfalfa and alfalfa/grass mixtures. ConclusionRelative feed value continues to be widely used asan index to assess quality, compare forage varieties,and price forages. However, differences in thedigestibility of the fiber fraction can result in a differ-ence in animal performance when forages with a simi-lar RFV index are fed. The RFQ index has been developed to overcome thisdifference. This index takes into consideration the dif-ferences in digestibility of the fiber fraction and can beused to more accurately predict animal performanceand match animal needs. Although hay base prices vary with supply anddemand, the market premium for quality is fairly con-stant. Long-term auction data indicate that the premiumfor quality forage is worth $0.90/ton as RFQ changesfrom one value to another; therefore improving RFQ ofharvested forage can improve profitability.ReferencesCollins, M. 1988. Composition and fiber digestion in morpho-logical components of alfalfa-timothy sward. Anim Feed DciTech 19:135-143.Dunham, J.R. 1998. Relative feed value measures forage quality.Forage Facts# 41. KState AES and CES.Undersander, D., and J.E. Moore. Relative forage quality. Focuson Forage, accessed at  http://www.uwex.edu/ces/crops/uwforage/RFQvsRFV.htm#homeUndersander, D. 2003. The new Relative Forage Quality Index-concept and use. World’s Forage Superbowl Contest, UWEX.3Table 3. Forage quality needs of cattle by relative     forage quality.Relative ForageQuality Suggested Cattle Type100-200 Heifer, 18-24 moDry cow115-130 Heifer, 12-18 mo Beef cow and calf125-150 Dairy, last 200 daysHeifer, 3-12 moStocker cattle140-160 Dairy, 1st three months of lactationDairy calfSource: Undersander (2003)Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the USDA. Larry Tidemann, Directorof Extension, Associate Dean, College of Agriculture & Biological Sciences, South Dakota State University, Brookings. SDSU is an AffirmativeAction/Equal Opportunity Employer (Male/Female) and offers all benefits, services, and educational and employment opportunities without regardfor ancestry, age, race, citizenship, color, creed, religion, gender, disability, national origin, sexual preference, or Vietnam Era veteran status.  ExEx8149, August 2004. Access at http://agbiopubs.sdstate.edu/articles/ExEx8149.pdfRFQ vs. RFV608010012014016018020022024070 85 100 115 130 145 160 175 190Relative Feed ValueRelative Forage QualityFig 1. Relative Forage Quality versus Relative Feed Value.

Understanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ)

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Understanding Relative Feed Value (RFV) and Relative Forage Quality (RFQ)

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