AS1250 (Revised May 2018) Quality Forage Forage Nutrition for Ruminants

Reviewed by Feed costs represent the single Forage Terminology Greg Lardy largest expense in most livestock Department Head operations. Producing and Plant Structure Animal Sciences Department properly preserving high-quality Forages have been described as forages can help reduce the bulky feeds that have relatively costs associated with feeding low digestibility. However, corn Plants utilized in feeding concentrates and supplements. silage is a forage, but it can be livestock have long been a Astute producers recognize more than 70 percent digestible. fundamental link in the food the economic significance of Perhaps the best way to under- chain. Native grasses supported producing high-quality stand forages is to look at the grazing animals well before forage crops. properties that make them unique. man began to domesticate The primary methods of Forages contain significant livestock. Forages always have harvesting and preserving portions of plant cell-wall been an extremely important forage crops include silage material. From the standpoint source of nutrients in livestock making, hay making, green of a forage user, the amount and rations. Ruminants, with their chopping and pasturing. type of plant cell wall is extremely symbiotic relationships with Each of these methods of forage important because it greatly microbes, are able to utilize harvest and/or preservation has influences how a particular forage forages as a primary portion benefits and limitations. Any will be utilized by animals to of their diet. Through their given operation may use each produce meat or milk. conversion into milk and of the methods at varying times, depending on the availability A young plant cell has a single meat products, forages of resources. Producers must outer layer referred to as the continue to be one of the review each management primary cell wall. Later, as the primary sources of nourishment practice and evaluate their own plant matures, a second layer is in the human diet. production situation to determine laid down on the inside of the which method to use to gain the cell. This is called the secondary maximum economic return. cell wall. The secondary wall is thicker and gives the plant cell tensile strength. The main structural components of the primary and North Dakota State University secondary walls are the complex Fargo,1 • AS1250 Forage North Dakota Nutrition for Ruminants carbohydrates, cellulose and This complex compound gives the Forage Evaluation hemicellulose. Together, the plant additional tensile strength primary and secondary cell and rigidity. Lignin can be thought Visual Appraisal walls make up a large portion of as the primary skeleton of the Measuring quality with visual of the forage (40 to 80 percent). plant cell. It is important from a appraisal, such by as sight, smell nutritional perspective because and feel, has distinct limitations, Humans and other monogastric it is a nondigestible substance but they are important tools for species have limited ability to and its presence limits the ability evaluating forages. Color; leaf digest plant cell wall compounds. of the microorganisms to ferment content; stem texture; maturity; Forage eaters, however, have the cellulose and hemicellulose contamination from weeds, bacteria and other microbial portions of the forage. molds or soil; and observations populations in their digestive on palatability are examples of A simplified analogy is to think of tracts than can ferment these useful visual determinations. the young plant cell wall as a wall compounds into usable nutrients. containing two layers. The initial Animals that have the ability to “Wet Chemistry” Analysis primary cell wall is the outer brick utilize forages as the primary Traditional laboratory methods wall, lacking mortar. The second- portion of their diet do not have involve various chemical, ary cell wall is like cinder blocks the enzymes necessary to digest drying and burning procedures on the inside of the brick wall, but the cellulose and hemicellulose to determine the major chemical also lacking mortar. The brick and compounds found in forages components in the forage. block could be broken down by themselves. They must rely on This is the older, well-established the microbial populations in the the microbial populations in method of forage analysis. digestive tract of the animal. their digestive system. Wet chemistry procedures are Lignin represents the mortar With advancing growth and the most widely used for forage that is added later to cement maturity, forage cells insert a evaluation in this country. the cell building blocks together. noncarbohydrate material, The procedures are based on As the plant advances in maturity, known as lignin, into the sound chemical and biochemical more and more lignin is added to primary and secondary walls. principles and take considerably the complex of brick and blocks, more time to complete than making them more difficult the newer electronic methods. to break down. Accurate results are dependent on good sampling techniques when the samples are gathered, proper handling of the samples after collection and good analyti- cal procedures in the laboratory conducting the evaluation.

■ ■ ■ The forage analysis is only as good as the sampling, handling and analytical procedures used.

Figure 1. Diagram of a plant cell showing cell wall structure. ■ ■ ■

2 • AS1250 Forage Nutrition for Ruminants Proximate Analysis because of the volatile fermenta- When excessive heating has This wet chemistry set of proce- tion products that are used by the occurred in the forage, such dures analyzes for the following: animal. Dry matter is also very as in poorly managed silage important because the moisture or hay, a portion of the crude • Dry matter content (100 percent content will give clues as to how a protein may be unavailable. minus moisture content) forage will preserve when stored The crude protein analysis gives • Crude protein (total nitrogen by baling or ensiling. no indication that excessive is measured) heating may have rendered a • Ether extract (lipids and fats) Protein Analysis portion of the protein unavail- • Ash (mineral content) Protein is an important nutrient able. If heat damage is suspected, • Crude fiber (most of the supplied by forages. In legumes, an analysis for bound protein or cellulose and some lignin) protein is the primary nutrient unavailable or insoluble protein supplied and is likely the principle should be requested. Laboratories Using this analysis, the proximate reason a particular forage is being typically report the bound protein system estimates the following: fed. Understanding what protein as ADF-CP, unavailable or • Nitrogen-free extract analysis tells about the quantity insoluble crude protein. (sugars, starch and some of and quality of the protein in the A portion of the crude protein the hemicellulose and lignin) forage is important. in forages always is unavailable; • Total digestible nutrients the percentage will increase if (estimate of digestibility) When a laboratory uses wet chemistry, crude protein most heating has occurred. If the bound While the proximate system has likely will be measured by the or insoluble protein is greater than some limitations for the analysis of standard Kjeldahl procedure. 12 percent of the crude protein, forages, portions of it are widely This measures total nitrogen, enough heating has occurred used today. Most typical forage which then is multiplied by to reduce protein digestibility. analyses use the dry-matter and 6.25 to arrive at the crude If the bound protein exceeds crude-protein procedures from protein value for the forage. 15 percent, extensive heating the proximate system to deter- The 6.25 figure is used because has occurred in the forage. mine percent of dry matter and most proteins contain about In formulating rations, the crude protein. Ash (total mineral 16 percent nitrogen (100 divided normal amount of bound protein content) and ether extract are not by 16 = 6.25). The crude protein has been taken into account when determined commonly in a typical value includes true protein and determining protein requirements forage analysis. The original crude nonprotein nitrogen compounds. for animals. Unless heating in fiber analysis has been replaced True-plant protein is roughly the feed has occurred, the crude with the newer detergent analysis. 70 percent of the protein in fresh protein value can be used in forages, 60 percent of the total formulation of the ration. If the Dry-matter Determination in hay forage and less than amount of bound protein is higher Dry matter is the percentage 60 percent in fermented forages. than 12 percent, available crude of the forage that is not water. Ruminant animals are able to protein (ACP) should be used. Dry-matter content is important utilize a portion of both types because all animal requirements of protein. Crude Fiber Analysis are made on a dry-matter basis. Many laboratories report Crude fiber determination was Comparing different forages a digestible protein value. the primary analytical procedure without using the percent of This is a calculated number, used to analyze forage samples for dry matter as a baseline would such as 70 percent of the crude many years. Crude fiber analysis be impossible. The dry matter protein or crude protein minus uses alkali and acid treatments of fermented feeds (haylage and 4.4. It is an estimate of protein to isolate the cell wall residue silage) often is underestimated digestibility only and has limited (crude fiber) that represents value in formulating rations. undigestible portions of the

3 • AS1250 Forage Nutrition for Ruminants of the cell wall well enough to The steps used to calculate the percentage of bound protein generate accurate energy estimates and available crude protein (ACP) are: for a wide range of forages species 1. Find the percentage of the crude protein that is bound. and maturities. The crude fiber Bound protein may be expressed as ADF-CP or Insoluble CP. system was criticized for often underestimating good-quality Example: forages and overestimating Crude Protein = 17.68% poor-quality forages. Figure 2 ADF-CP = 2.36% shows how the crude fiber and % bound = 2.36 ÷ 17.68 = 13.35% the newer detergent systems fractionate forages. Because this value exceeds 12 percent, it indicates heating has occurred in the forage and available protein should be calculated The Van Soest or detergent sys- and used. tem of forage analysis is the most common way to partition forages. 2. Calculate percentage of ACP. The forage sample is boiled in a Example: special detergent at a neutral pH % ACP = [CP% x (100 – (% bound – 12%))] ÷ 100 of 7.0. The material then is filtered. The soluble portion contains these % ACP = [17.68 x (100 – (13.35 - 12))] ÷ 100 = 17.44 highly digestible cell contents: Note: The ACP value in this case is lower than crude protein, • sugars 17.68, because the bound protein value is greater than 12 percent. • starch If the forage analysis reports the bound protein as bound • pectins nitrogen (ADIN), the bound crude protein can be determined • lipids (fat) by multiplying by 6.25. • soluble carbohydrates Example: • protein ADIN = 0.29% (dry basis) • nonprotein nitrogen Bound crude protein is: 0.29 x 6.25 = 1.81% • water-soluble vitamins and minerals Some laboratories report percent ACP as crude protein minus bound protein. Technically, this is incorrect because it does not account for Neutral Detergent Fiber the normal amount of bound protein in the forage. (NDF) and Acid Detergent Fiber (ADF) The insoluble portion of the forage. Researchers later learned Detergent or Van Soest forage (neutral detergent that ruminants could digest Method of Cell Wall fiber) contains the cellulose, a portion of the crude fiber. Determination hemicellulose, lignin and silica. It commonly is referred to as the Even with its faults, the crude A newer method for evaluating cell wall fraction. Research shows fiber system provides valuable the cell wall content of forages neutral detergent fiber (NDF) information concerning the was developed in the 1960s by is negatively correlated with nutritive value of forages. Peter Van Soest at the U.S. dry-matter intake. In other words, A modified version of the Department of Agriculture- as the NDF in forages increases, crude fiber analysis (MCF) Agricultural Research Service’s animals will consume less forage. that includes the insoluble ash Beltsville Agricultural Research NDF increases with the advanc- still is used in portions of the Center (BARC) in Maryland. ing maturity of forages. A better country to evaluate alfalfa. This system was developed prediction of forage intake can because research determined that be made using NDF; therefore, the crude fiber system did not better rations can be formulated. differentiate the components

4 • AS1250 Forage Nutrition for Ruminants The fraction of the forage cell wall In contrast to nonstructural The NDSC include structural and that is most commonly isolated carbohydrates (NSC), also referred fiber carbohydrates (Figure 4). and reported is the acid detergent to as non-fiber carbohydrates As a class, NDSC are highly fiber (ADF). This may be the most digestible (see Van Soest, Figure 3) (NFC), the carbohydrates in important determination of the and rapidly fermented. However, question are actually neutral forage analysis. they are a compositionally diverse detergent-soluble carbohydrates group, which has tended to Acid detergent fiber is the (NDSC). preclude their direct measurement portion of the forage that remains by chemical analysis. after treatment with a detergent under acid conditions. It includes the cellulose, lignin and silica Table 1. Classification of forage fractions using the Van (Figure 2). Acid detergent fiber is Soest method. important because it is negatively correlated with how digestible Nutritional Availability a forage may be when fed. Fraction Components included Ruminant Non-ruminant As the ADF increases, the Cell • sugars, starch, pectin complete complete forage becomes less digestible. contents • soluble carbohydrates complete complete • protein, nonprotein N high high Acid detergent fiber sometimes • lipids (fats) high high • other solubles high high is misinterpreted as indicating the acid content of fermented Cell wall • hemicellulose partial low (NDF) • cellulose partial low forages. The term acid detergent • heat-damaged protein indigestible indigestible fiber has nothing to do with • lignin indigestible indigestible the acid content of a forage. • silica indigestible indigestible The name is derived from the Source: Van Soest, JAS 26:119. procedure used to determine the cellulose and lignin content.

Lignin, the indigestible noncarbohydrate component that decreases cellulose and hemicellulose availability, can be determined by further treatment with a stronger acid. Figure 3 shows a schematic of the detergent system of a forage analysis. Table 1 classifies the digestibility of forage fractions using the Van Soest method. The average cell contents and cell wall fractions for forages common to our area are listed in Table 2.

Neutral Detergent-soluble Carbohydrates (NDSC) The carbohydrates soluble in neutral detergent include the most digestible portion of the plant and are the most difficult to describe nutritionally. Figure 2. Fractions of feed dry matter.

5 • AS1250 Forage Nutrition for Ruminants NDSC is calculated as the difference between NDF and noncarbohydrate fractions by the equations:

100 – (crude protein + NDF + ether extract + ash) or 100 – ((crude protein + (NDF – NDIN) + ether extract + ash))

The second equation corrects for protein in the NDF and avoids subtracting the protein twice.

Because it is calculated by Figure 3. difference, all of the errors Schematic of the detergent from the component analyses system of forage analysis. accumulate in NDSC.

The source of crude protein in a feed may be a source of error in the NDSC calculation. Crude protein is simply an estimation of protein mass arrived at by Table 2. Average cell contents and cell wall fractions in multiplying nitrogen content common forages. by 6.25. When the nitrogenous Forage Cell Contents NDF ADF Crude Fiber Lignin compounds present are not Percent, Dry-matter Basis one-sixteenth nitrogen, factors Alfalfa other than 6.25 may be late vegetative 60 40 29 22 7 appropriate. However, no early bloom 58 42 31 23 8 midbloom 54 46 35 26 9 practical way is available to full bloom 50 50 37 29 10 determine the correct multiplier. Red clover 44 56 41 9 10 The effect of miscalculating Birdsfoot trefoil 53 47 36 31 9 crude protein mass in the NDSC calculation is of special Brome late vegetative 35 65 35 30 4 concern with feeds high in late bloom 32 68 43 37 8 nonprotein nitrogen.

Orchardgrass One of the greatest challenges midbloom 32 68 41 33 6 late bloom 28 72 45 37 9 to using NDSC in ration Sorghum-sudangrass 32 68 42 36 6 formulation is its diversity of components. The NDSC includes Timothy late vegetative 45 55 29 27 3 organic acids, sugars, disaccha- midbloom 33 67 36 31 5 rides, oligosaccharides, starches, late bloom 32 68 55 31 7 fructans, pectic substances, Corn silage ß-glucans and other carbohydrates stover 32 68 55 31 7 soluble in neutral detergent. well eared 49 51 28 24 4 few ears 47 53 30 32 5 Different carbohydrates Source: U.S.-Canadian tables of feed composition, third revision. 1982. predominate in the NDSC of different feeds. Beyond their

6 • AS1250 Forage Nutrition for Ruminants composition, these carbohydrates upon the current situation, Mineral Analysis also vary in their digestion and more work needs to be done Forage analyses typically report fermentation characteristics to determine how to formulate the content of major minerals. (Table 3). rations optimally using the The minerals typically determined different fractions and how to Organic acids, such as acetate are calcium and phosphorus. separate organic acids from sugars and lactate, do not support In laboratories using wet and starches to better predict microbial growth to the extent chemistry, atomic absorption and nutrients available to the animal. of other carbohydrates. The rate colorimetric procedures are used of starch fermentation in the most commonly to determine the rumen is highly variable and mineral content of the forage. changes with the processing method, source and other ration components. Pectic substances support a microbial yield similar to starch, but their fermentation is depressed at low pH.

Thus far, differences in NDSC among feeds have been used in a qualitative fashion for ration formulation because no practical way is available to measure the component carbohydrates. Recent work offers a way of analyzing feeds to separate neutral detergent-soluble fiber from starches, sugars and organic acids. Although this improves Figure 4. Carbohydrate composition of chemically analyzed fractions.

Table 3. Characteristics of neutral detergent-soluble carbohydrates (NDSC).

Digestible by May Ferment Fermentation Predominant Mammalian to Lactic Depressed NDSC Fraction Composition Enzymes1 Acid1 at Low pH1 Common Sources Organic acids acetate propionate, yes no no silage, feed, additives, whey lactate, butyrate Sugars and glucose, fructose, yes yes no molasses, citrus pulp, disaccharides sucrose (glucose + fructose) sugar beet pulp Starch glucose yes yes no corn and small grain products, difference bakery waste, potatoes Fructans fructose no yes unknown temperate cool season grasses, Jerusalem artichoke Pectic galacturonic acid, arabinose, no no yes legume forages, citrus pulp, substances galactose, rhamnose, etc. beet pulp, soybean hulls ß-glucans glucose no no yes/unknown small grains

1 Relative to starch. Reference: M.B. Hall, U.S. Forage Research Center

7 • AS1250 Forage Nutrition for Ruminants Near-infrared Reflectance distinguish color when light The typical forage analysis Spectroscopy (NIRS) strikes a material that absorbs generated with NIRS is similar Analysis some wavelengths and reflects to that using proximate Near-infrared reflectance others. and detergent analysis. spectroscopy is a rapid and The detection of specific nutrients low-cost computerized method is possible because reflectance In addition, NIRS typically to analyze forage and grain spectra from forage samples of reports bound protein, crops for their nutritive value. established nutrient values (by available crude protein, Instead of using chemicals, wet chemistry procedures) are potassium and as in conventional methods, programmed into the computer. magnesium values. NIRS uses near-infrared light When a similar feed sample is to determine protein, fiber, evaluated by NIRS, the computer In Vitro and In Vivo energy and mineral content. compares the wavelength Disappearance Evaluation This method of analysis involves reflections caused by the In vivo (in animal) and in vitro (in the drying and grinding of sample and matches them to glass or in test tube) procedures samples, which then are exposed previously tested samples. are seldom used for farm forage to infrared light in a spectropho- The NIRS method of determining analysis. However, scientists tometer. The reflected infrared forage nutritional content is commonly use them to evaluate radiation is converted to electrical very rapid and less expensive forage quality. Most often, dry- energy and fed to a computer than wet chemistry methods. matter disappearance in a specific for interpretation. Each major Accuracy depends on good period of time is measured, and organic component of forages sample collection, storage and this value will indicate how (and grain) will absorb and reflect consistent drying, grinding digestible a forage may be. near-infrared light differently. and mixing of samples prior to By measuring these different analysis. The calibration set that The term in situ (in bag) may be reflectance characteristics, is used must be developed from used to describe the procedure the NIRS unit and a computer an adequate number of wet in which small polyester bags determine the quantity of these chemistry samples similar to containing samples of forage components in the feed. those being analyzed. Without are placed in the rumen of live animals consuming similar diets The procedure is similar to proper calibration, the NIRS to the forage being evaluated. the human ability to visually analysis can have serious errors. This is done through a sealed ex- ternal opening into the rumen of an animal, called a canula.

In vitro is usually a two-step procedure done in test tubes. First the forage sample is digested using rumen fluid from a donor animal to simulate rumen diges- tion. The sample then is digested in an acidic enzyme solution to simulate digestion in the true stomach (abomasum).

In situ and in vitro are excellent techniques for forage evaluation when more expensive and time- Figure 5. Diagram of how NIRS reads a prepared plant sample. consuming digestion or feeding trials are not possible.

8 • AS1250 Forage Nutrition for Ruminants Digestion trials are an excellent While TDN values are common the usable energy content of feeds way to evaluate forages or other on forage analysis reports, TDN can be made. Seeing the terms feeds for nutrient availability. is not commonly used in ration net energy-maintenance (NEM), formulation because it does not net energy-gain (NEG) and net In this procedure, the forage is fed account for all the losses that can energy-lactation (NEL) is very to several animals. The amount of occur in the fermentation and common on laboratory or NIRS forage fed and feces produced in metabolism when forages are fed. forage reports. These terms are a 10- to 14-day period is recorded These losses can be large for used commonly in formulating and sampled for analysis. forages, so improved energy today’s rations. Figure 6 shows An estimate of digestibility can estimate systems have been the losses subtracted to arrive then be calculated as follows: developed. at these energy terms. ((dry-matter intake – dry-matter The total energy content of a output feces) ÷ dry-matter intake) Energy Terminology feed can be determined by bomb x 100 = apparent dry-matter digestibility Consumed forage can be calorimetry (completely burning) thought of as a fuel and the the sample and measuring the Example: In a digestion trial using animal that consumes it as six animals, the average feed intake heat produced to obtain the gross and fecal production were: a vehicle. No vehicle is energy value of the feed. However, 100 percent efficient at burning it does not indicate how digestible ((48 lb. – 17.8) ÷ 48) x 100 = 62.9% apparent dry-matter digestibility fuel. No animal uses 100 percent the feed is. For example, wood of the forage to produce the chips and corn grain have about Because an analysis can be products we derive from them. the same gross energy value, but done on the feed and feces, if both were fed, the digestibility By accounting for losses during determining the digestibility would be very different. Table 4 digestion, absorption and for each nutrient in the feed is compares some common forages. utilization, better predictions of possible. For example, the protein digestibility could calculate to be 75 percent digestible while the cell wall fractions may be only Gross Energy 59 percent digestible. In scientific Energy lost in fecal material research, this procedure is (Portion of feed not digested) followed to determine total digestible nutrients (TDN). Digestible Energy

The actual formula is: Energy lost in urine Also methane (gas) loss in ruminants % digestible crude protein + (from fermentation in the ruman) % digestible crude fiber + Metabolizable Energy % digestible starch and sugars + % digestible fats x 2.25 = % TDN Losses from the production of heat - Heat of metabolism The fats are multiplied by 2.25 - Heat produced in digestive tract because they contain that much Net Energy more energy per unit weight.

Total digestible nutrients may be Energy used for Energy used estimated when the forage analy- maintenance for production of animal sis is determined using the proxi- (NEM) mate analysis. This is done using Gain Milk - Lactation average digestion numbers from (NEG) (NEL) previous digestion trials. Figure 6. Energy losses when forages are fed.

9 • AS1250 Forage Nutrition for Ruminants Table 4. Four forages showing total digestible nutrient and net energy values.1 Forage Terms

Net Energy, Mcal Per Pound Digestible Dry Matter (DDM) Forage % TDN Maintenance Gain Lactation Many forage analyses will Bermudagrass, 43 to 56 day growth 43 0.33 0.09 0.42 include a value called digestible Alfalfa hay, full bloom 55 0.52 0.26 0.56 dry matter. While different Alfalfa hay, late vegetative 63 0.64 0.38 0.65 laboratories may use different Corn silage, well eared 70 0.74 0.47 0.73 formulas to calculate this value, 1All values on a dry-matter basis. one common formula is: Source: NRC, Nutrient Requirements of Dairy Cattle, 1989, 2001. 88.9 – (0.779 x % ADF) = %DDM Example: If % ADF = 31%: 4. Laboratory digestibility and Important Points 88.9 – (0.779 x 31) = 64.75% 1. Net energy values for forages net energy values are not produced from digestion are best for ration formulation Dry-matter Intake (DMI) because they account for the trials or metabolism studies. Feeding studies have shown that major losses in digestion and The feeding value of forges as the percent of NDF increases utilization of the feed. has been shown to be associated negatively with in forages, animals consume less. 2. Each feed has three net energy cell wall contents (as the ADF Therefore, the percent of NDF can values because animals use and NDF values go up, energy be used to estimate dry-matter feeds with different efficien- values decrease). Because of intake. The formula used for cies, depending on how the this, energy values, estimates the calculation is: energy is being utilized. Net of digestibility and relative feed energy-gain is the least efficient 120 ÷ %NDF = DMI values reported on laboratory (as a percent of body weight) and will have the lowest value. analysis are calculated using NEM and NEL are utilized with the ADF content in the forage. Example: about equal efficiencies because Neutral detergent fiber content NDF value for a forage is 40%: milk is predominantly water is used to estimate the amount 120 ÷ 40 = 3% of body weight DMI (about 87 percent). In most of forage an animal will be dairy formulations, the same able to consume. Relative Feed Value (RFV) value is used for NE and NE . M L The dry-matter intake potential 3. Total digestible nutrients, (DMI) may not be reported as which are calculated from The fact that ADF and NDF such, but it may be used to digestion trials, do not account calculate a term called relative for all the losses. Forages tend values are used to generate feed value (RFV). This combines to have a large loss of energy many of the relative feeding dry-matter intake and the digest- due to fermentation in the values further emphasizes ible dry-matter (DDM) values of rumen of the animal. Unless the importance that cell the forage. it is below the thermal neutral wall content has on animal zone of the animal, this heat performance. (%DDM x %DMI) ÷ 1.29 = RFV loss represents total loss to Example: the animal. For this reason, From the previous examples TDN tends to overestimate DDM = 64.75%, DMI = 3.0% the energy value of forages. (64.75 x 3) ÷ 1.29 = 151 Therefore, net energy values, This estimates the intake of not TDN, normally are used digestible dry matter relative to a in ration formulation. forage that contains 1.29 percent of body weight as digestible dry matter and represents the quality

10 • AS1250 Forage Nutrition for Ruminants of an average to below average Table 5. Relative feed values of various forages. forage. Forage CP ADF NDF RFV Relative feed value has no units, ———————— % ———————— but it is a way to compare the Alfalfa, pre-bud 23 28 38 164 potential of two or more like Alfalfa, bud 20 30 40 152 Alfalfa, mid-bloom 17 35 46 125 forages for energy intake. Alfalfa, mature 15 41 53 100 Forages with NDF values of Alfalfa-grass, bud 19 30 45 135 53 percent and ADF values of Alfalfa-grass, mid-bloom 15 38 55 100 41 percent represent the value Alfalfa-grass, mature 12 42 52 101 of 100 RFV (typical first-cutting Brome, late vegetative 14 35 63 91 alfalfa in full bloom). Brome, late bloom 8 49 81 58 Bermudagrass, early 12 32 70 85 Forages with values greater Bermudagrass, late 8 43 78 66 than 100 are of higher quality. Corn silage, well eared 9 28 48 133 If a forage has a value lower than Corn silage, few ears 8 30 53 115 100, it is lower in value compared Cornstalks 6 43 68 76 with the forage with 53 percent Sorghum-sudangrass, vegetative 15 29 55 112 NDF and 41 percent ADF. Note Surghum-sudangrass, headed 8 40 65 83 Wheat straw 4 54 85 51 that the forage with an RFV of 100 would not be considered excellent-quality forage. Dairy producers with high-producing As a result, the RFV index has and scale the same as with RFV. cows often require RFVs of come under increasing scrutiny Dairy-quality hay will still score 150 or greater. as scientists have learned more above 150, for example. about fiber digestibility. Relative feed values do not take On average, alfalfa will get into account the protein content A forage’s energy content has a the same scores as it does now. of the forage. Protein content lot to do with the digestibility of Individual samples, though, has to be evaluated separately. its fiber, and forages similar in may differ by up to 50 points Table 5 shows forages with most other quality parameters can when evaluated by RFQ instead different relative feed values vary widely in fiber digestibility. of RFV. But the results will more and expected CP levels. The current RFV formula uses accurately reflect the forage’s ADF to estimate energy content. true value. However, ADF only explains Relative Feed Quality (RFQ) In general, grasses will get about 55 percent of the variation Recently approved, relative feed higher scores under RFQ. in the digestibility of a forage. quality (RFQ) is an improved They tend to be high in NDF, version of RFV. Developed by the The proposed RFQ will predict so they score too low when all University of Wisconsin, it adds the energy content and potential fiber is assumed to be equally measures for fiber digestibility as intake of forages, just as RFV does. digestible. Changing RFV likely well as quantity. The difference: With RFQ, NDF will broaden its applicability. digestibility will be included in The proposed new RFQ index, both calculations. originally called digestible relative feed value (dRFV), will replace That’s because digestibility RFV is appropriate only for RFV, which was implemented impacts the energy content of alfalfa and cool-season grasses, in 1978. Although RFV is used a forage as well as the amount although it often is used more widely. widely, what has become apparent animals will eat. To avoid The new index probably can is that hay lots with identical confusion and ensure broad be used on corn silage and RFV scores don’t necessarily acceptance of the switch to RFQ, perhaps other types of forage, too. produce the same amount of milk. the scientists kept the numbers

11 • AS1250 Forage Nutrition for Ruminants The equations have been validated RFQ Index not only in Wisconsin but also in numerous other environments RFQ = (DMI, % of BW) x (TDN, % of DM) ÷ 1.23 from California to New York. When the divisor, 1.23, is used to adjust the equation to have a mean and range similar to RFV (Moore and Undersander, 2002, Proc. Natl. Forage Testing Assn.). Because regression equations are difficult and somewhat 1) For alfalfa, clovers and legume/grass mixtures, the equations for TDN and DMI time-consuming in a production will be: field situation, tables have been Total digestible nutrients for alfalfa, clovers and legume/grass mixtures are calculated from NRC 2001 recommendations using in vitro estimates of digestible developed using computer NDF as follows: spreadsheet programs that help make for rapid in-field estimates TDNlegume= (NFC x 0.98) + (CP x 0.93) + (FA x 0.97 x 2.25) + (NDFn x (NDFD ÷ 100) – 7 of NDF or relative feed value where: CP = crude protein (% of DM) (RFV). EE = ether extract (% of DM) Additionally, several seed FA = fatty acids (% of DM) = ether extract – 1 companies have developed NDF = neutral detergent fiber (% of DM) “PEAQ sticks” that can be used NDFCP = neutral detergent fiber crude protein easily to determine plant height NDFn = nitrogen-free NDF = NDF – NDFCP, else estimated as NDFn = NDF x 0.93 and forage quality. The original NDFD = 48-hour in vitro NDF digestibility (% of NDF) “five maturity stage” system used NFC = nonfibrous carbohydrate (% of DM) = 100 – (NDFn + CP + EE + ash) with PEAQ has been simplified to a “three maturity stage” system Dry matter intake calculations for alfalfa, clover and legume/grass mixtures without a loss of precision. will be:

DMIlegume = 120 ÷ NDF + (NDFD – 45) x .374 ÷ 1350 x 100 with NDFD adjustment. 45 is an average value for fiber digestibility of alfalfa and Estimating Alfalfa RFV alfalfa/grass mixtures. in the Field Using PEAQ DMI is expressed as % of body weight (BW), NDF as % of DM and NDFD as % of NDF Step 1 Select a representative 2) For warm- and cool-season grasses, the equations for TDN and DMI will be: 2-foot-square area in the field. Total digestible nutrients for warm- and cool-season grasses are calculated as:

TDNgrass = (NFC x 0.98) + (CP x 0.87) + (FA x 0.97 x 2.25) + Step 2 (NDFn x NDFDp ÷ 100) – 10 Determine the stage of growth Where terms are as defined previously and NDFDp = 22.7 + .664 x NDFD for the most mature alfalfa plant Dry-matter intake calculations for warm- and cool-season grasses will be: stem in the selected area by

2 DMIGrass = -2.318 + 0.442 x CP - 0.0100 x CP – 0.0638 x TDN + 0.000922 x referring to Table 6, Alfalfa growth TDN2 + 0.180 x ADF – 0.00196 x ADF2 – 0.00529 x CP x ADF stages. An example log sheet has

DMI is expressed as % of BW, and CP, ADF and TDN are expressed as % of DM been provided on Page 14.

Step 3 Predictive Equations The two equations predict ADF Select the tallest most mature for Alfalfa Quality and NDF when the height of alfalfa plant within the 2-foot- the tallest stem is measured and Predictive equations for alfalfa square area. Measure the height the maturity stage of the most quality (PEAQ) is a method to from the soil surface (next to the advanced plant is determined. predict the forage quality of plant crown) to the top of the stem standing alfalfa. It was developed by agronomists at the University Many state and county Extension staff are using PEAQ along with other of Wisconsin - Madison. methods to help farmers predict the optimum harvest time for alfalfa. This has proved especially useful for first cutting.

12 • AS1250 Forage Nutrition for Ruminants (not the tip of the highest leaf Table 7. Predictive Equation of Alfalfa Quality (PEAQ). blade). Straighten the stem Stage of Most Mature Stem for an accurate measure of Height of LATE BUD STAGE FLOWER STAGE its length and record your tallest stem VEGETATIVE 1 or more nodes 1 or more measurement in inches. (from soil surface Vegetative (<12”) with visible buds. nodes with to stem tip) No buds visible. No flowers visible. open flower(s). Note: The tallest stem may not be the most 16 237 225 210 mature stem. Do your measurements on the tallest stem with the most 17 230 218 204 mature stage of growth. 18 224 212 198 19 217 207 193 Step 4 20 211 201 188 Based on the length of the 21 205 196 183 tallest and most mature stem, use Table 7, Predictive Equation of 22 200 190 178 Alfalfa Quality (PEAQ), to estimate 23 195 185 174 relative feed value (RFV) based on 24 190 181 170 plant height and maturity value. 25 185 176 166 26 180 172 162 Step 5 27 175 168 158 For best results, repeat steps 28 171 164 154 1 to 4 in multiple (four or five) representative areas in your 29 167 160 151 field and average the results. 30 163 156 147 Sample more times for fields 31 159 152 144 larger than 30 acres. 32 155 149 140 Note: This procedure estimates alfalfa 33 152 145 137 relative feed value for a standing 34 148 142 134 crop. PEAQ does not account for changes in quality because of 35 145 139 131 wilting, harvesting, weather damage 36 142 136 128 and storage. To estimate harvested 37 138 133 126 relative feed values, subtract 15 to 20 RFV units (assuming good 38 135 130 123 wilting and harvesting conditions) 39 132 127 121 from the calculated values. 40 129 124 118 This procedure is most accurate for a good stand of pure alfalfa 41 127 122 115 with healthy growth. 42 124 119 113

The PEAQ system for estimating alfalfa quality in the field was developed by agronomists at the University of Wisconsin - Madison.

Table 6. Alfalfa growth stages.

Maturity Value Description Late vegetative (L) Stem length >12 inches Keep in mind: To target 150 RFV alfalfa in storage, Bud stage (B) 1 or more nodes start cutting at 170 RFV to compensate with visible buds. No flowers visible. for harvesting losses, which can account Flower stage (F) 1 or more nodes for 10 percent to 15 percent reduction with open flower(s). in quality from respiration and leaf loss.

13 • AS1250 Forage Nutrition for Ruminants PEAQ Log Sheet Plant Maturity Date Field Identification Height Value Est. RFV Comments 5/23 North 80 29 B 160 example entry

14 • AS1250 Forage Nutrition for Ruminants Formulas Used in Forage Analysis Reports

Various laboratories may 1. Estimating Percent Digestible Protein (DP): use different formulas for Corn silage: % DP = (% crude protein x 0.908) – 3.77 reporting calculated values or for forages. Some of the more = crude protein x 0.70 common ones are shown. Alfalfa: % DP = % crude protein – 4.4 or Note that because the = % crude protein x 0.72 same formulas are not used by all laboratories, 2. Estimating Percent TDN: comparing the values Legumes and grasses: = 88.9 – (0.79 x ADF%) from one laboratory with those of another Corn silage: = 87.84 – (0.70 x ADF%) may not be possible. 3. Estimating Net Energy-Lactation, Mcal/lb: Alfalfa: = 1.044 – (ADF% x 0.0123) Grasses: = 1.50 – (ADF% x 0.0267) Alfalfa – grass mixtures: = 1.044 – (ADF% x 0.0131) or = (TDN% x 0.1114) - 0.054

4. Estimating Percent Digestible Dry Matter (DDM): % DDM = 88.9 – (ADF% x 0.779)

5. Estimating Dry-matter Intake as a Percent of Body Weight (DMI): % DMI = 120 ÷ % NDF

6. Relative Feed Value (RFV): RFV = (%DDM [from No. 4 above] x %DMI [from No. 5 above]) ÷ 1.29

7. Relative Feed Quality (RFQ): RFQ = (TDN [from No. 2 above] x DMI [from No. 5 above]) ÷ 1.23

15 • AS1250 Forage Nutrition for Ruminants NDSU EXTENSIONNDSU SERVICE EXTENSION SERVICE

Other publications in the Quality Forage series

➤ AS1251 “Interpreting Composition and Determining Market Value” ➤ AS1252 “Haylage and Other Fermented Forages” ➤ AS1253 “Corn Silage Management” ➤ AS1254 “Silage Fermentation and Preservation” ➤ AS1255 “Storage, Sampling and Measuring” ➤ AS1256 “Stressed or Damaged Crops”

References

In addition to sources cited, materials were adapted with permission from Pioneer Forage Manual, which no longer is in print.

Replaces AS991, “Know Your Forages”

This publication was authored by J.W. Schroeder, former dairy specialist, NDSU, 2006.

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