Forage Nutrition For Ruminants AS1250 Quality Forage Series

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AS1250(Revised May 2018)Quality ForageForage Nutritionfor RuminantsReviewed byGreg LardyDepartment HeadAnimal Sciences DepartmentPlants utilized in feedinglivestock have long been afundamental link in the foodchain. Native grasses supportedgrazing animals well beforeman began to domesticatelivestock. Forages always havebeen an extremely importantsource of nutrients in livestockrations. Ruminants, with theirsymbiotic relationships withmicrobes, are able to utilizeforages as a primary portionof their diet. Through theirconversion into milk andmeat products, foragescontinue to be one of theprimary sources of nourishmentin the human diet.North Dakota State UniversityFargo,North Dakota1 AS1250Forage Nutrition for RuminantsFeed costs represent the singlelargest expense in most livestockoperations. Producing andproperly preserving high-qualityforages can help reduce thecosts associated with feedingconcentrates and supplements.Astute producers recognizethe economic significance ofproducing high-qualityforage crops.Forage TerminologyThe primary methods ofharvesting and preservingforage crops include silagemaking, hay making, greenchopping and pasturing.Each of these methods of forageharvest and/or preservation hasbenefits and limitations. Anygiven operation may use eachof the methods at varying times,depending on the availabilityof resources. Producers mustreview each managementpractice and evaluate their ownproduction situation to determinewhich method to use to gain themaximum economic return.Forages contain significantportions of plant cell-wallmaterial. From the standpointof a forage user, the amount andtype of plant cell wall is extremelyimportant because it greatlyinfluences how a particular foragewill be utilized by animals toproduce meat or milk.Plant StructureForages have been described asbulky feeds that have relativelylow digestibility. However, cornsilage is a forage, but it can bemore than 70 percent digestible.Perhaps the best way to understand forages is to look at theproperties that make them unique.A young plant cell has a singleouter layer referred to as theprimary cell wall. Later, as theplant matures, a second layer islaid down on the inside of thecell. This is called the secondarycell wall.The secondary wall is thickerand gives the plant cell tensilestrength. The main structuralcomponents of the primary andsecondary walls are the complex

carbohydrates, cellulose andhemicellulose. Together, theprimary and secondary cellwalls make up a large portionof the forage (40 to 80 percent).Humans and other monogastricspecies have limited ability todigest plant cell wall compounds.Forage eaters, however, havebacteria and other microbialpopulations in their digestivetracts than can ferment thesecompounds into usable nutrients.Animals that have the ability toutilize forages as the primaryportion of their diet do not havethe enzymes necessary to digestthe cellulose and hemicellulosecompounds found in foragesthemselves. They must rely onthe microbial populations intheir digestive system.With advancing growth andmaturity, forage cells insert anoncarbohydrate material,known as lignin, into theprimary and secondary walls.This complex compound gives theplant additional tensile strengthand rigidity. Lignin can be thoughtof as the primary skeleton of theplant cell. It is important from anutritional perspective becauseit is a nondigestible substanceand its presence limits the abilityof the microorganisms to fermentthe cellulose and hemicelluloseportions of the forage.A simplified analogy is to think ofthe young plant cell wall as a wallcontaining two layers. The initialprimary cell wall is the outer brickwall, lacking mortar. The secondary cell wall is like cinder blockson the inside of the brick wall, butalso lacking mortar. The brick andblock could be broken down bythe microbial populations in thedigestive tract of the animal.Lignin represents the mortarthat is added later to cementthe cell building blocks together.As the plant advances in maturity,more and more lignin is added tothe complex of brick and blocks,making them more difficultto break down.Forage EvaluationVisual AppraisalMeasuring quality with visualappraisal, such by as sight, smelland feel, has distinct limitations,but they are important tools forevaluating forages. Color; leafcontent; stem texture; maturity;contamination from weeds,molds or soil; and observationson palatability are examples ofuseful visual determinations.“Wet Chemistry” AnalysisTraditional laboratory methodsinvolve various chemical,drying and burning proceduresto determine the major chemicalcomponents in the forage.This is the older, well-establishedmethod of forage analysis.Wet chemistry procedures arethe most widely used for forageevaluation in this country.The procedures are based onsound chemical and biochemicalprinciples and take considerablymore time to complete thanthe newer electronic methods.Accurate results are dependenton good sampling techniqueswhen the samples are gathered,proper handling of the samplesafter collection and good analytical procedures in the laboratoryconducting the evaluation. The forage analysisis only as goodas the sampling,handling and analyticalprocedures used.Figure 1. Diagram of a plant cell showing cell wall structure.2 AS1250Forage Nutrition for Ruminants

Proximate AnalysisThis wet chemistry set of procedures analyzes for the following: Dry matter content (100 percentminus moisture content) Crude protein (total nitrogenis measured) Ether extract (lipids and fats) Ash (mineral content) Crude fiber (most of thecellulose and some lignin)Using this analysis, the proximatesystem estimates the following: Nitrogen-free extract(sugars, starch and some ofthe hemicellulose and lignin) Total digestible nutrients(estimate of digestibility)While the proximate system hassome limitations for the analysis offorages, portions of it are widelyused today. Most typical forageanalyses use the dry-matter andcrude-protein procedures fromthe proximate system to determine percent of dry matter andcrude protein. Ash (total mineralcontent) and ether extract are notdetermined commonly in a typicalforage analysis. The original crudefiber analysis has been replacedwith the newer detergent analysis.Dry-matter DeterminationDry matter is the percentageof the forage that is not water.Dry-matter content is importantbecause all animal requirementsare made on a dry-matter basis.Comparing different forageswithout using the percent ofdry matter as a baseline wouldbe impossible. The dry matterof fermented feeds (haylage andsilage) often is underestimated3 AS1250 Forage Nutrition for Ruminantsbecause of the volatile fermentation products that are used by theanimal. Dry matter is also veryimportant because the moisturecontent will give clues as to how aforage will preserve when storedby baling or ensiling.Protein AnalysisProtein is an important nutrientsupplied by forages. In legumes,protein is the primary nutrientsupplied and is likely the principlereason a particular forage is beingfed. Understanding what proteinanalysis tells about the quantityand quality of the protein in theforage is important.When a laboratory uses wetchemistry, crude protein mostlikely will be measured by thestandard Kjeldahl procedure.This measures total nitrogen,which then is multiplied by6.25 to arrive at the crudeprotein value for the forage.The 6.25 figure is used becausemost proteins contain about16 percent nitrogen (100 dividedby 16 6.25). The crude proteinvalue includes true protein andnonprotein nitrogen compounds.True-plant protein is roughly70 percent of the protein in freshforages, 60 percent of the totalin hay forage and less than60 percent in fermented forages.Ruminant animals are able toutilize a portion of both typesof protein.Many laboratories reporta digestible protein value.This is a calculated number,such as 70 percent of the crudeprotein or crude protein minus4.4. It is an estimate of proteindigestibility only and has limitedvalue in formulating rations.When excessive heating hasoccurred in the forage, suchas in poorly managed silageor hay, a portion of the crudeprotein may be unavailable.The crude protein analysis givesno indication that excessiveheating may have rendered aportion of the protein unavailable. If heat damage is suspected,an analysis for bound protein orunavailable or insoluble proteinshould be requested. Laboratoriestypically report the bound proteinas ADF-CP, unavailable orinsoluble crude protein.A portion of the crude proteinin forages always is unavailable;the percentage will increase ifheating has occurred. If the boundor insoluble protein is greater than12 percent of the crude protein,enough heating has occurredto reduce protein digestibility.If the bound protein exceeds15 percent, extensive heatinghas occurred in the forage.In formulating rations, thenormal amount of bound proteinhas been taken into account whendetermining protein requirementsfor animals. Unless heating inthe feed has occurred, the crudeprotein value can be used informulation of the ration. If theamount of bound protein is higherthan 12 percent, available crudeprotein (ACP) should be used.Crude Fiber AnalysisCrude fiber determination wasthe primary analytical procedureused to analyze forage samples formany years. Crude fiber analysisuses alkali and acid treatmentsto isolate the cell wall residue(crude fiber) that representsundigestible portions of the

The steps used to calculate the percentage of bound proteinand available crude protein (ACP) are:1. Find the percentage of the crude protein that is bound.Bound protein may be expressed as ADF-CP or Insoluble CP.Example:Crude Protein 17.68%ADF-CP 2.36%% bound 2.36 17.68 13.35%Because this value exceeds 12 percent, it indicates heating hasoccurred in the forage and available protein should be calculatedand used.2. Calculate percentage of ACP.Example:% ACP [CP% x (100 – (% bound – 12%))] 100% ACP [17.68 x (100 – (13.35 - 12))] 100 17.44Note: The ACP value in this case is lower than crude protein,17.68, because the bound protein value is greater than 12 percent.If the forage analysis reports the bound protein as boundnitrogen (ADIN), the bound crude protein can be determinedby multiplying by 6.25.Example:ADIN 0.29% (dry basis)Bound crude protein is: 0.29 x 6.25 1.81%Some laboratories report percent ACP as crude protein minus boundprotein. Technically, this is incorrect because it does not account forthe normal amount of bound protein in the forage.forage. Researchers later learnedthat ruminants could digesta portion of the crude fiber.Even with its faults, the crudefiber system provides valuableinformation concerning thenutritive value of forages.A modified version of thecrude fiber analysis (MCF)that includes the insoluble ashstill is used in portions of thecountry to evaluate alfalfa.4 AS1250 Forage Nutrition for RuminantsDetergent or Van SoestMethod of Cell WallDeterminationA newer method for evaluatingthe cell wall content of forageswas developed in the 1960s byPeter Van Soest at the U.S.Department of AgricultureAgricultural Research Service’sBeltsville Agricultural ResearchCenter (BARC) in Maryland.This system was developedbecause research determined thatthe crude fiber system did notdifferentiate the componentsof the cell wall well enough togenerate accurate energy estimatesfor a wide range of forages speciesand maturities. The crude fibersystem was criticized for oftenunderestimating good-qualityforages and overestimatingpoor-quality forages. Figure 2shows how the crude fiber andthe newer detergent systemsfractionate forages.The Van Soest or detergent system of forage analysis is the mostcommon way to partition forages.The forage sample is boiled in aspecial detergent at a neutral pHof 7.0. The material then is filtered.The soluble portion contains thesehighly digestible cell contents: sugars starch pectins lipids (fat) soluble carbohydrates protein nonprotein nitrogen water-soluble vitamins andmineralsNeutral Detergent Fiber(NDF) and Acid DetergentFiber (ADF)The insoluble portion of theforage (neutral detergentfiber) contains the cellulose,hemicellulose, lignin and silica.It commonly is referred to as thecell wall fraction. Research showsneutral detergent fiber (NDF)is negatively correlated withdry-matter intake. In other words,as the NDF in forages increases,animals will consume less forage.NDF increases with the advancing maturity of forages. A betterprediction of forage intake canbe made using NDF; therefore,better rations can be formulated.

The fraction of the forage cell wallthat is most commonly isolatedand reported is the acid detergentfiber (ADF). This may be the mostimportant determination of theforage analysis.Acid detergent fiber is theportion of the forage that remainsafter treatment with a detergentunder acid conditions. It includesthe cellulose, lignin and silica(Figure 2). Acid detergent fiber isimportant because it is negativelycorrelated with how digestiblea forage may be when fed.As the ADF increases, theforage becomes less digestible.Acid detergent fiber sometimesis misinterpreted as indicatingthe acid content of fermentedforages. The term acid detergentfiber has nothing to do withthe acid content of a forage.The name is derived from theprocedure used to determinethe cellulose and lignin content.In contrast to nonstructuralcarbohydrates (NSC), also referredto as non-fiber carbohydrates(NFC), the carbohydrates inquestion are actually neutraldetergent-soluble carbohydrates(NDSC).The NDSC include structural andfiber carbohydrates (Figure 4).As a class, NDSC are highlydigestible (see Van Soest, Figure 3)and rapidly fermented. However,they are a compositionally diversegroup, which has tended topreclude their direct measurementby chemical analysis.Table 1. Classification of forage fractions using the VanSoest method.Nutritional AvailabilityFractionComponents includedRuminantNon-ruminantCellcontents sugars, starch, pectin soluble carbohydrates protein, nonprotein N lipids (fats) other tehighhighhighCell wall(NDF) hemicellulose cellulose heat-damaged protein lignin urce: Van Soest, JAS 26:119.Lignin, the indigestiblenoncarbohydrate componentthat decreases cellulose andhemicellulose availability,can be determined by furthertreatment with a stronger acid.Figure 3 shows a schematic ofthe detergent system of a forageanalysis. Table 1 classifies thedigestibility of forage fractionsusing the Van Soest method.The average cell contents and cellwall fractions for forages commonto our area are listed in Table 2.Neutral Detergent-solubleCarbohydrates (NDSC)The carbohydrates soluble inneutral detergent include themost digestible portion of theplant and are the most difficultto describe nutritionally.5 AS1250Forage Nutrition for RuminantsFigure 2. Fractions of feed dry matter.

NDSC is calculated as thedifference between NDF andnoncarbohydrate fractionsby the equations:100 – (crude protein NDF ether extract ash)or100 – ((crude protein (NDF –NDIN) ether extract ash))The second equation corrects forprotein in the NDF and avoidssubtracting the protein twice.Because it is calculated bydifference, all of the errorsfrom the component analysesaccumulate in NDSC.Figure 3.Schematic of the detergentsystem of forage analysis.Table 2. Average cell contents and cell wall fractions incommon forages.ForageCell ContentsNDFADFCrude FiberLigninPercent, Dry-matter BasisAlfalfalate vegetative60402922early bloom58423123midbloom54463526full bloom5050372978910Red clover445641910Birdsfoot trefoil534736319Bromelate vegetative356535304late bloom326843378Orchardgrassmidbloom326841336late te vegetative455529273midbloom336736315late bloom326855317Corn silagestover32685531well eared49512824few ears47533032Source: U.S.-Canadian tables of feed composition, third revision. 1982.6 AS1250 Forage Nutrition for Ruminants745The source of crude protein in afeed may be a source of error inthe NDSC calculation. Crudeprotein is simply an estimationof protein mass arrived at bymultiplying nitrogen contentby 6.25. When the nitrogenouscompounds present are notone-sixteenth nitrogen, factorsother than 6.25 may beappropriate. However, nopractical way is available todetermine the correct multiplier.The effect of miscalculatingcrude protein mass in theNDSC calculation is of specialconcern with feeds high innonprotein nitrogen.One of the greatest challengesto using NDSC in rationformulation is its diversity ofcomponents. The NDSC includesorganic acids, sugars, disaccharides, oligosaccharides, starches,fructans, pectic substances,ß-glucans and other carbohydratessoluble in neutral detergent.Different carbohydratespredominate in the NDSC ofdifferent feeds. Beyond their

composition, these carbohydratesalso vary in their digestion andfermentation characteristics(Table 3).Organic acids, such as acetateand lactate, do not supportmicrobial growth to the extentof other carbohydrates. The rateof starch fermentation in therumen is highly variable andchanges with the processingmethod, source and other rationcomponents. Pectic substancessupport a microbial yield similarto starch, but their fermentationis depressed at low pH.upon the current situation,more work needs to be doneto determine how to formulaterations optimally using thedifferent fractions and how toseparate organic acids from sugarsand starches to better predictnutrients available to the animal.Thus far, differences in NDSCamong feeds have been used ina qualitative fashion for rationformulation because no practicalway is available to measurethe component carbohydrates.Recent work offers a way ofanalyzing feeds to separateneutral detergent-soluble fiberfrom starches, sugars and organicacids. Although this improvesMineral AnalysisForage analyses typically reportthe content of major minerals.The minerals typically determinedare calcium and phosphorus.In laboratories using wetchemistry, atomic absorption andcolorimetric procedures are usedmost commonly to determine themineral content of the forage.Figure 4. Carbohydrate composition of chemicallyanalyzed fractions.Table 3. Characteristics of neutral detergent-soluble carbohydrates (NDSC).PredominantNDSC FractionCompositionDigestible byMammalianEnzymes1May Fermentto LacticAcid1FermentationDepressedat Low pH1Common SourcesOrganic acidsacetate propionate,yesnonosilage, feed, additives, wheylactate, butyrateSugars anddisaccharidesglucose, fructose,yesyesnosucrose (glucose fructose)Starchglucoseyesyesnodifferencemolasses, citrus pulp,sugar beet pulpcorn and small grain products,bakery waste, potatoesFructansfructosenoyesunknowntemperate cool season grasses,Jerusalem artichokePecticsubstancesgalacturonic acid, arabinose,galactose, rhamnose, etc.nonoyeslegume forages, citrus pulp,beet pulp, soybean hullsß-glucansglucosenosmall grainsRelative to starch.Reference: M.B. Hall, U.S. Forage Research Center17 AS1250 Forage Nutrition for Ruminantsnoyes/unknown

Near-infrared ReflectanceSpectroscopy (NIRS)AnalysisNear-infrared reflectancespectroscopy is a rapid andlow-cost computerized methodto analyze forage and graincrops for their nutritive value.Instead of using chemicals,as in conventional methods,NIRS uses near-infrared lightto determine protein, fiber,energy and mineral content.This method of analysis involvesthe drying and grinding ofsamples, which then are exposedto infrared light in a spectrophotometer. The reflected infraredradiation is converted to electricalenergy and fed to a computerfor interpretation. Each majororganic component of forages(and grain) will absorb and reflectnear-infrared light differently.By measuring these differentreflectance characteristics,the NIRS unit and a computerdetermine the quantity of th

1 AS1250 Forage Nutrition for Ruminants AS1250 (Revised May 2018) Quality Forage Feed costs represent the single largest expense in most livestock operations. Producing and Plant Structure properly preserving high-quality forages can help reduce the costs associated with feeding

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