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Introduction

The producer of ruminant livestock canprotect profits by managing land for optimalpasture production. Acomplex array of deci-sions on the use and ma-nipulation of plant andanimal species and man-agement contribute to thecentral goal of meetingthe livestock nutrient re-quirements primarilythrough grazing, with aminimum of harvestedforages and purchasedfeedstuffs.

A major problemencountered in trying tomeet nutritional requirements of animals frompasture is that most ruminant nutrition researchhas been conducted with harvested forages. Many of the typical livestock feedingrecommendations are questionable, becausethey were either not developed from grazing-based research at all or were developed undergrazing that was poorly managed. For example,low forage quality is most frequently given asthe reason for the poor performance of grazinganimals. In reality, the reason is probably aninadequate availability of quality forage, which isprimarily determined by how pastures aremanaged.

Nutritional Parameters and ForageAvailability

Estimates of dry matter intake based onnutritional parameters(acid detergent fiberand neutral detergentfiber) probablyunderestimatepotential intake byanimals, under goodgrazing managementwith adequateamounts of forage. The most commonlypublished estimates ofintake by livestock,particularly beef cattle,are too low forproductive animals.

How much cattle eat on pasture is determinednot only by quality parameters but also by theamount of forage available and by the grazingbehavior of the animal.

Research indicates that cattle will takeabout 30,000 bites a day. If the pasture is ofsufficient height or density, the animal can get a"mouthful" with each bite. For cattle, this heightis 6-10 inches, averaging 1800-2400 pounds ofdry matter per acre for cool-season grasses andlegumes. Bermuda grass need not be as tallbecause it is denser. When dry matteravailability drops below 1000-1200 pounds peracre, the intake decreases significantly. Sheepwill graze closer to the ground than cattle orgoats. Goats need a higher availability of foragethan cattle or sheep, as they tend to graze higheron the plant. When available forage falls belowthe dry matter threshold (forage is 3-4 inchestall), total intake drops. The animal mayincrease grazing time to some degree, but

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What�s Inside Nutritional Parameters & Forage Availability ........................................................ 1 Supplemental Feeding ................................................. 3 Feed Budgeting & Management................................... 4 Suggested Reading...................................................... 5 Enclosures.................................................................... 5

LIVESTOCK TECHNICAL NOTES

MEETING THE NUTRITIONAL NEEDS

OF RUMINANTS ON PASTURE

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usually not enough to offset the decline in bitesize. Production decreases because livestock aresimply unable to consume enough nutrientseven though forage quality may be adequate.

Estimates of fiber (ADF and NDF) andcrude protein (CP) are excellent indicators forevaluating the nutrient value of harvestedforages, but should be used carefully in regardto grazing animals. These parameters primarilyreflect the stage of maturity of plants whenharvested. The intent of a good grazingmanagement program is to keep the plantsvegetative. If that is accomplished, other factorswill influence animal production more, and theestimates of fiber and crude protein will be lessuseful as grazing behavior and quantity ofavailable forage will have a greater impact ontotal nutrient intake than quality. In fact, mostpastures, with the exception of some nativewarm season grasses, when kept in thevegetative state are 12-25% CP so that theconcern actually becomes one of wastingprotein, not suffering a shortage of it. The ratioof nitrogen to energy can be too high for goodperformance in that energy required to use theprotein (nitrogen) will be taken from theproduction of the animal, which is therebydecreased. Without energy available to use theexcess nitrogen, it is excreted. In such cases, thequality of the forage is too high, as measured byhigh protein and low fiber, i.e., the forage is too�vegetative�, containing too much degradableprotein and not enough digestible fiber. This canbe of concern to grass-based dairy producers. Some producers have reported incidences ofacidosis when grazing highly vegetativepastures. Cows also tend to lose body conditionbecause they use body fat as an energy sourcewhen the carbon to nitrogen ratio is out ofbalance.

Ruminants grazing pasture require twotypes of digestible protein. Non-proteinnitrogen is degraded in the rumen (rumendegradable protein). The N is used by therumen microbes to produce microbial protein. The other type is escape or bypass protein,which is not degraded in the rumen (rumenundegradable protein) and is digested in the

small intestine. The degradable protein needsmust be met before a benefit of escape proteinwill occur. That is the reason low qualityforages (less than 6-8% CP) should besupplemented with a degradable protein suchas soybean meal. This happens mostly with therange-type grasses and very seldom with cool-season grasses in a grazing situation. The nativewarm-season grasses, such as switchgrass, arethought to have more bypass protein and mayat times benefit from a degradable proteinsupplement whereas a cool season grass such astall fescue or bromegrass has a largerdegradable protein component. This alsoexplains why producers who use cool seasongrasses for hay do not necessarily need proteinsupplementation, particularly if the hay is cut atthe proper time.

Most vegetative forages, particularlycool season grasses and legumes that do notcontain tannins, contain high levels of CP, ofwhich about 70-80% is degraded in the rumenfor use by the rumen microbes while 20-30%escapes to the small intestine for absorption. Astandard recommendation is that 62-68% of thetotal protein should be rumen degradable. Thissituation varies with type of plant and grazingmanagement. The protein in legumes, such asbirdsfoot trefoil, is less degradable in the rumenbecause of tannin content.

Grazing management decisions have animpact on total diet quality. When animalsselectively graze as in slow rotations, theyconsume the leafy, vegetative forage first,whereas in a daily rotation animals are more aptto eat the whole plant including a higherpercentage of stems. This is because the stockdensity is high enough that the animals must eatmore than just the tops of the plants. The use ofcrude protein in determining quality of pastureis misleading due to a lack of knowledge abouthow much of the protein is degraded where. Recent research indicates that if the animal eatsa diet with more stems, provided the stems arestill immature, rather than grazing the tops(leaves), less percentage of the protein isdegraded in the rumen, and it is better utilized. An example is grazing alfalfa with a high stock

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density (daily rotation) versus a low stockdensity where selective grazing determineswhat part of the plant the animal consumes. When the animal eats the whole plant, there is ahigher level of undegradable protein ascontrasted to when the animal only eats the top(leaves).

Supplemental Feeding

After grazing management,supplemental feeding can have the next mostimportant impact on animal production. Normally we think of supplemental feeding inconjunction with low quality forages. However,we now believe we can increase production inanimals that have potential for highperformance and are grazing high-qualityforages by furnishing either rumen-escapeprotein or a source of energy to better utilize thesoluble protein being degraded in the rumen. Insuch cases supplementation is justified bypotential profits, especially if the feed isproduced on the farm. Thus, the return can beinfluenced by type of forages being grazed, asmentioned earlier. One must know about levelsof degraded and escape protein to properlysupplement the grazing animal.

On the other hand, supplementationsometimes interferes with digestibility if thelevel of grain is too high. Until recently, about1% of body weight was the recommended levelof grain to feed. For example, a 500-pound steerwould have been fed five pounds of grain on adry matter basis. Now the recommended levelis .3% or 1-2 pounds for that same steer becauseresearch indicates that the higher grain levelinterfered with fiber digestion. This is due tothe fact that different rumen microbes areresponsible for fiber digestion. It may not beeconomical to feed the higher level of grainbecause of the reduced efficiency of grainconversion at levels higher than 0.5% of bodyweight. Another question is when to feedsupplements. Research shows that feedingsteers on pasture during the morning hoursdecreases intake by interfering with normalgrazing patterns of the animal. Feeding in theafternoon is preferable.

Another area of concern regardingsupplemental feed is in grass-based dairyproduction. Excellent research in grazing dairycows is being conducted at the Penn StateUniversity Grazing Research and EducationCenter. The recommendations from thisresearch indicate that the best way to utilizehighly degradable protein is to provide energyfrom shelled corn or other grains. Energy islimiting when pastures are the major source offorage. If energy is lacking and the rumendegradable protein is high, the rumen ammoniais converted to urea, which appears in the bloodand milk and eventually excreted in the urine. Formation and excretion of urea requiresenergy, which could be used by the cow formilk production or gain. Since energy isnecessary for optimum reproduction and sincegrazing cows have a higher level of activity thancows in confinement, the supplementation ofadditional energy should be considered. Research shows that cows on pasture havelower body condition. Therefore, whensupplementing with grain, the body conditionof the cow should be considered in additionamount of milk produced by the cow.

An interest in by-product feeds, such ascorn gluten feed, wheat middlings, brewersgrain, rice bran, and soyhulls has developedbecause these feedstuffs are high in digestiblefiber and do not negatively impact foragedigestion the way grains do. Fibrous feeds havean energy value about 85% that of corn. Supplementation studies have shown them toproduce gains equivalent to those from cornsupplementation. They have polysaccharidessimilar to forages, which means these feedssupport the growth of rumen microbesresponsible for forage digestion. Therefore,these by-product feeds can be used tosupplement high-quality pasture withoutdecreasing forage intake or digestibility. Thesefeeds have become quite popular with dairyproducers, and are receiving considerableattention from other livestock producersbecause of the above-mentioned benefits. Askyour local extension person or feedrepresentative for more information on by-product feeds.

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Feed Profiling, Feed Budgeting andManagement of Rotations

In the US we are accustomed to allowinglivestock access to pasture without any forwardplanning. In other words, too often producersjust turn cattle on pasture without planninghow to manage the pasture to stretch feedsupplies or how to extend the grazing season. Ifpasture is not sufficient, production decreasesand/or we have to supplement with harvestedor purchased supplements which are usuallyexpensive. The point is we need to have morecontrol consumption and growth of pasture. Hence the term controlled grazing.

In New Zealand two useful concepts,feed budgeting and feed profiling, are used toplan the management of pastures. Feed profilingis used to determine the type of livestockproduction system that matches the quantityand quality of forage on the farm. Long termplanning must include feed profiling.Management decisions such as optimum milkproduction, breeding season and calving(lambing, kidding), or when to purchase andsell animals determine the efficiency of alivestock enterprise on pasture.

Feed budgeting is more of a short-termevaluation of forage availability, growth rateand animal demand. This process isparticularly useful when surplus or shortage ofpasture is developing. By forward planning wecan match the nutritional requirements of theanimals with availability of quality forage fromgrazing. This requires timing parturition withgrass production, fertilizing at the proper timefor optimal growth, making short-term livestockmanagement decisions to match nutritionalrequirements with available forage, and usinggrazing management techniques to efficientlyutilize forage. A skillful manager canmanipulate quality and quantity. Animals do notneed maximum intake at all times. If we determinethe critical time periods when maximum weightgain is necessary, pasture can be rationed atother times, making more efficient utilization ofthe pasture. A producer may develop a feedingplan based on how much each animal should

eat for optimal production. Note that optimumis not necessarily maximum production. Veryfew animals need maximum intake every day ofthe year.

Pasture rationing can be accomplishedthrough the use of electric fencing in much thesame way as putting feed into a trough. Rationing is best accomplished through rotationof livestock every 1-3 days. Higher producinganimals may be grazed on pastures first andthen rotated to a fresh paddock when theavailable dry matter is down to 1200-1500pounds per acre. In order to have high-qualitypastures for the next rotation, the paddocksshould probably be grazed down to 800-1000pounds of dry matter using animals that have alower nutrition requirement. Intake of foragedecreases rapidly as dry matter availabilitydrops below 1200 pounds. This practice isreferred to as first and second grazers or follow-up grazing in New Zealand. Proper grazingallows for more efficient utilization of pastureand increases the gain per acre of land inproduction.

It is useful to note that beef cattlemaintain better intake levels as pasture declinesthan do sheep and goats. Goats, in particular,will decrease grazing time as forage availabilitydeclines. Therefore, cattle may be a betterchoice than sheep or goats to "clean up"pastures, but only if they have low nutritionrequirements, such as nonlactating cows inadequate condition for calving.

Paddocks, which are out of control, wheregrowth is slowing because of the reproductivestage of plant growth, are best removed from agrazing rotation and harvested for hay. Thepaddock can be added back to the rotation at alater time when it will be higher quality and willextend the grazing season through the summer. Had the paddock been grazed instead, then a highpercentage of the pasture would have been wastedthrough trampling and forage quality would havebeen marginal for maximum performance. Also,regrowth would have been limited unless thepaddock were mowed or brushhogged aftergrazing.

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Summary

The information presented here isintended to give an overview of theconsiderations in raising livestock on grass andminimizing the use of grain and harvestedfeedstuffs. Several steps are involved inplanning a grazing system to meet thenutritional requirements of ruminants.

� Inventory the pastures. Determine when thebest quantity of high-quality forage isavailable and establish the animalproduction system that utilizes forage mostefficiently.

� Know the nutritional requirements ofvarious classes of animals and how tomanipulate those requirements (earlyweaning in extremely dry weather, forexample) to match the forage resources withnutritional needs.

� Learn to assess the forage and determinewhether the animals are getting optimalintake. Remember that many nutritionrecommendations are based on harvestedforages and are questionable under goodgrazing management.

� Remember that nutritional requirements ofanimals are actually based on the amount ofnutrient intake and not on a percentage. In agrazing situation, where animals are on ahigh-quality forage, the animal may nothave to consume as much forage every dayto meet its requirements, particularly forprotein.

� Remember that cool-season grasses, warm-season grasses and legumes differ innutrient content. This is certainly criticalwhen evaluating research results in oneregion of the country as to application inanother area. Of greatest importance isresearch on supplementation of pasture;therefore, one needs to know what species of

forages were used in research beforetransferring the results.

Suggested reading:

Forage-Animal Management Systems by Roy Blaser. 1986. 90 p. Virginia Tech University.Grazing Management by John F. Vallentine. 1990. 533 p.

Grazing Management: Science into Practice by JohnHodgson. 1990. 203 p.

Livestock Feeding on Pasture by the New ZealandSociety of Animal Production. 1987. 145 p.

Pastures: Their Ecology and Management by R.H.M.Langer. 1990. 490 p.

The Ecology and Management of Grazing Systems byJ. Hodgson and A. W. Illius. 1996. 466p.

Enclosures:

Holden, L 1998. Feed budgeting with pasture. Pas-ture Talk, Vol. 4, No. 1.

Klopfenstein, T. 1996. Need for escape protein bygrazing cattle. Animal Feed Science Technology60:191-1909.

Gerrish, J. and R. Morrow. 1997. Grazing basics. Missouri Grazing Manual, University of Missouri,Columbia.

Muller, L. D. 1996. Nutritional considerations fordairy cattle on intensive grazing systems. 1996Maryland Grazing Conference.

Prepared by Ron MorrowNCAT Agriculture Specialist

June 1998 CT082

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