Concern among some dairy nutritionists has recently been expressed that  high potassium  content of hay and silage is reducing milk production in some high-producing dairy herds. Alfalfa and grass hay and com and grass silage, which have been heavily fertilized, are the objects of this concern. The nutritional question being considered in this article is whether an animal diet excessively high in potassium (

Dougherty, C. T.

Mitchell, G. E.

Wells, Kenneth L.

English

University of Kentucky

University of KentuckyUKnowledgeAgronomy Notes Plant and Soil Sciences1995Sodium in Pasture Species and Grazing LivestockC. T. DoughertyUniversity of KentuckyKenneth L. WellsUniversity of KentuckyG. E. MitchellUniversity of KentuckyRight click to open a feedback form in a new tab to let us know how this document benefits you.Follow this and additional works at: https://uknowledge.uky.edu/pss_notesPart of the Agronomy and Crop Sciences CommonsThis Report is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in AgronomyNotes by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu.Repository CitationDougherty, C. T.; Wells, Kenneth L.; and Mitchell, G. E., "Sodium in Pasture Species and Grazing Livestock" (1995). Agronomy Notes.37.https://uknowledge.uky.edu/pss_notes/37UNIVERSITY OF KENTUCKYCOLLEGE OF AGRICULTURELexington, Kentucky 40546COOPERATIVE EXTENSION SERVICEronomynoleBVol. 28, No.5, 1995Sodium in Pasture Species and GrazingLivestock©C.T. Dougherty, K.L. Wells, and G.E. MitchellIntroductionConcern among some dairy nutri-tionists has recently been expressedthat "high potassium" content of hayand silage is reducing milk productionin some high-producing dairy herds.Alfalfa and grass hay and com andgrass silage, which have been heavilyfertilized, are the objects of this con-cern. The nutritional question beingconsidered in this article is whether ananimal diet excessively high in potas-sium (1<) is likely to bring on sodium(Na) deficiency in the animal due toion antagonism. If, in fact, this is thecase, a knowledge of Na accumula-tion by forages and the need to offsetsueh an imbalance by feeding supple-mental Na becomes important.Salt (sodium chloride:NaCI) fer-tilizationofpastures has been recentlyproposed in a popular dairy publica-tion as a means ofpromoting produc-tion of grazing dairy cows. Thatarticle was based on British researchon dairy cows grazing perennialryegrass pastures and has spurredconsiderable interest among dairyfarmers. Salt fertilization may appearto bean attractiveoption to salt supple-mentation because of its low cost, oras a partial substitute for more expen-sive K fertilizers, and because it mayreduce some ofthe problems ofdairycows reportedly associated with for-ages with a high K content (>4% K inDM). A review of sodium in plantsand animals seems appropriate at thistime.Role of Na in Animalsand PlantsThe ionic nature of Na and K re-sults in their being mutually competi-tive in biological systems. In fact,there is substantial evidence that eachcan substitute for thy '6ther to somedegree in cellular functions. Thefollowing discussion highlights thecurrent knowledge about the role ofNa in plants and animals.Sodium in plantsSodium is not essential for plantgrowth, but it is considered beneficial.Plants can be classified according totheirNauptake. Halophytes are plantsthat have evolved a tolerance to Naand are adapted to saline soils. An-other class, natrophiles (salt-lovingplants), also known as Na accumula-tors, have variable Na concentrationsin their tissues, depending on the Nacontent ofthe soil. Sodium accumula-tors increase their Na content in re-sponse to fertilization with salt.Natrophobes (salt-hating plants), alsoknown as non-accumulators of Na,typically have low Na concentrationsin their herbage «2 glkg). Even ifnon-accumulators are fertilized withsalt their herbage remains low in Na.Thereare two subclasses ofnon-accu-mulators. One class absorbs Na intoroots but40es nottranslocate Nato itsaerial parts. Another class absorbsvery little Na by selectively excludingit. A classification of most pasturespecies used in Kentucky according toNa type is shown in Table 1.Sodium content of herbageSome of the herbage species usedin Kentucky grassland agriculture donot have enough Na to meet the needsoflivestock, ifthey are the sole sourceoffeed. Content ofNa in forage DMranges from 0.005% to 2.13 %, withan average of0.22% (Table 2). Thelower levels may be those ofherbageof non-accumulators or of Na accu-mulators grown on soils of low Nacontent. Herbage grown on soilsheavily fertilized with K may be oflow Na content because uptake of Kby plants invariably depresses Nauptake. Red clover and alfalfa areknown to have low Na content. Sur-Educatronal programs of rhe Kentucky Cooperative Exlensl(Jn Service serve all people regardless 01 fsce. color, ag9, sex, feligion, disability, or national of/gm.UNIVERSITY OF KENTUCKY, KENTUCKY STATE UNIVERSITY, U.S. DEPARTMENT OF AGRICULTURE, AND KENTUCKY COUNTIES, COOPERATINGAgronomy Notesprisingly,whitecloversuppliesenoughNa for livestock. Sodium content ofalfalfa herbage DM grown at the Uni-versity of Kentucky's Spindletop re-search fann in FayetteCounty in 1994ranged from 0.02 to 0.09 % with anaverage of0.04 %. Sub-tropical spe-cies, such as sudangrass, sorghum,crabgrass, pearl millet, andbermudagrass are low Na plants andmay be exceptions for they may actu-ally require some Na, albeit in verysmall amounts. Sudangrass appearsto be very low in herbage Na (Table2). Temperate grass species, such asannual and perennial ryegrass, andorchardgrass containsufficientNaforlivestock, but Na may be limiting intimothy. Classification oftall fescuewith regard to Na accumulation is notclear. The Na content of tall fescue(Table 2) and its close genetic rela-tionship to the ryegrasses would sug-gest that it is a Na accumulator.Sodium requirements ofanimalsAnimals need Na because it is theirmost important extracellular cation.Sodium has many functions in animalmetabolism, including electrolyte bal-ance, nutrient absorption and trans-port, water balance and in the centralnervous system. Bodies ofadult cattlecontain an average of 0.2% Na ofbody mass. Normally, only smallregular inputs of Na are needed, be-cause large Na reserves are main-tained in their extracellular fluid vol-ume (0.32 to 0.35% Na), particularlyin the fluid of the reticulo-rumen.About 0.15 % Na (1.5g Na/kg) inherbage dry matter (DM) maintainssatisfactory Na dietary levels in mostclasses of livestock, however, non-lactating beef cattle perfonn well at0.06 to 0.08% Na (6-8 g/kg) in herb-age OM. Lactating beef and dairycows need more Na (0.18 % Na or18g/kg) in diet DM "because largeamounts of Na are excreted in milk,which is relatively rich in Na(0.4% or4g/kg).Sodium deficiencyoflivestockhasbeen recognized fordecades. A recentsurvey revealed that most Kentuckybeef cattle producers fed salt, trace-mineralized saltora complete mineralmix to their herds. Recently, grazingsystems researchers at the ForageSystems Research Center of Univer-sity ofMissouri in Linneus found thatdiets of beef cattle grazing pastures,which are very similar to those ofKentucky, were deficient in Na allyear around. Salt-based mineral mix-tures are also routinely used to deliverother macronutrients, micronutrients,larvacides, rumen modifers (e.g.,monensin, lasalocid etc.) and bloat-preventing agents.Cattle, like humans, can discrimi-nate between salt, sweet, sour andbitter tastes. Theyalso havea specificappetite for salt and will, given theopportunity, consume much more saltthan they need for their physiologicalprocesses. If given the opportunity,livestock seJectively-graze plants thathave higher Na content and this maycompensate for ingestion of herbagethat is low in Na.Potential for NaDeficiency inLivestockSalt deficiency in livestock is ex-pressed in behavior such as languor,debility and pica (licking or eatingsoil), licking sweat off other animalsor drinking urine and usually is re-flected in low productivity. Manyresponses oflivestock toNa deficiencyare complex. The British researchmentioned previously showed that saltfertilization of perennial ryegrass (aNa accumulator) increased milkfatPage 2production from grazing dairy cowseven when dietary Na levels were ad-equate. It appears that Na substitutedfor K and delayed senescence ofplanttissues and this led to greater herbageintake.We might anticipate Na deficien-cies ofgrazing livestock in Kentuckyin the absence ofNa supplementationwhen the species being grazed is anon-accumulatorofNa, is underheavyK fertilization, is in monoculture, or isassociated with herbage or weed spe-cies that are also Na non-accumula-tors. This scenario may seem unlikelybut it describes a weed-free stand ofalfalfa, or an alfalfa stand with acomplement of crabgrass or foxtailthat is intensivelygrazed bybeefcattle,or one grown on high K soils. Sodiumdeficiencies are less likely to occur inweedy stands or in alfalfa-grass mix-tures where the sown grass is a Naaccumulator (e.g., orchardgrass).Their penchant for salt also explainswhy cattlemay selectivelygrazeweedsbefore they graze alfalfa. Animalbehavior experts do not regard suchresponses as examples of"nutritionalwisdom."At the University of KentuckySpindletop research farm, we foundthat salt applied to alfalfa canopiesincreased herbage DM intake of drybeef cows by 8%, a response appar-entlynot related to taste and measuredwithin days of removal offree-ehoicesalt supplements. We thought thatthis response may be caused by "cecaldilatation and torsion."In a series oflamb and beefstockergrazing trials on alfalfa in NewZealand, poor animal growth rateswere attributed to low Na content ofalfalfa herbage OM (0.03 to 0.04%Na). Death rates of lanlbs on weed-free alfalfa reached over 20%, soonafter lambs were exposed to alfalfa.Mortality of lambs receiving saltAgronomy Notessupplements or grazing weedy alfalfawas near zero. The weed herbage thatwas preferentially grazed had over 10times more Na than the alfalfa herb-age. Postmortems revealed the deathwas not due to legume bloat but to"intestinal torsion." Essentially, thehindgut rotated more than 270°, cut-ting offthe blood flow ofthe anteriormesenteric artery and causing mas-sive hemorrhaging of the intestines("red gut" syndrome). Hindgut oflambs that survived rotated less than90°. Intestinal torsion of sheep ap-pears similar to cecal dilatation andtorsion, supposedly a rare problem ofcattle and, possibly, to abomasal dis-placement frequently reported in dairycattle. Intestinal torsions may furtherintensifY Na deficiency by reducingthe volume ofthe Na reservoir. SomeUS scientists implicate Na and K intheetiology ofabomasal displacement.Thus, it is possible that "red gut syn-drome" ofsheep, cecal dilatation andtorsion and abomasal displacement ofcattle are expressions ofNa status ofanimal diet, moderated by differentmorphology of the ovine and bovinegastrointestinal tract.ImplicationsOneimplicationofthesalteconomyofpasture species is obvious. In Ken-tucky, grazing beefcattle need accessto salt supplements all year around.This is also the recommendation oftheForage Systems Research Center ofthe University ofMissouri. Fertiliza-tion of pastures with salt cannot el-evate the Na content of herbage ofpasture species that do not accumu-late Na sufficiently to meet animal Naneeds. As an example ofNa requiredby grazing cattle, consider the needsofa 1000 lb beefcow grazing alfalfa.In this case, she may eat 30 lb ofherbage DM per day. If the Na con-tent ofal fal fa herbage DM was 0.04%(0.4 gNalkg), she would ingest 0.012lb ofNa (5.44 g) from alfalfa herbageeach day. Because livestock require0.15 %Naintheir diet DM (1.5 glkg),this 1000 Ib cow needs 0.045 Ib Na(20.4 g). To provide her Na require-ments, herdiet shouldbe supplementedwit40.033 Ib Na each day. Thisistheequivalent ofO.0841b ofcommon saltper day (about 1.33 ounces).Fertilization of both Na accumu-lating and non-accumulating pasturespecies with K is likely to depressherbage Na content and, possibly, in-duce or intensifY Na deficiency inlivestock. Potassium fertilization ofgrazed alfalfa may further increasethe potential for K-induced Na defi-ciency in animals because most oftheingested herbage K is recycled backonto the field in urine. Grazed alfalfafields should be soil-tested each yearto determine the amount ofK fertilizerneeded.Sodium-accumulating grasses(orchardgrass or ryegrass) are prefer-able to Na non-accumulating grasses(timothy) as companion grasses inalfalfa-grass mixtures>SummarySome concern has been raised inKentuckythat feeding "high K" hayorsilage may cause a Na deficient diet indairy herds. At the current time, nosuch questions have been raised con-cerning Na deficiency in beef herds.This probably is due to alfalfa beingmuch less used in diets ofbeefherds,and the fact that beefherds are grazedon pasture while dairy herds are keptin drylots for confined feeding.Producers ofalfalfa hay and silageshouldnot "over-fertilize"alfalfa fieldseither with commercial fertilizers orwith animal manures. Annual soiltesting is the best way to determinewhether K fertilization is needed. Thebest way to reduce the potential for NaPage 3deficiency inanimal diets is to providesupplemental Na in mineral mixes or .as common salt to dairy and beefherds. This is of particular impor-tance where alfalfa is a major compo-nent of the animal diet.InformationResourcesBurris, WR, K Laurent, M Bertram &CW Absher. 1992. Characteristics ofKentucky cow-calf producers- a survey(unpublished).Carlson, G.P. 1989. Fluid, electrolyte, andacid-base balance. In n. Kaneko (edi-tor). Clinical BiochemislIy ofDomesticAnimals. 4th edition.Chiy CP & CJC Phillips. 199 J. The ef-fects of sodium chloride application topasture or its direct supplementation, ondail)' cow production and grazing prefer-enee. Grass & Forage Science. 46:325-33 J.Jaguseh KT, RC Gumbrell, MC Mobley& NP Jay. 1976. ElTects of saIl blocksand roughage as supplements to grazinglueeme 'on growth rate of lambs andincidence of deatlis from red gut. NewZealand Journal of Experimental Agri-culture, 5: 19-22.Jubb KVF, PC Kennedy & N Palmer.1993. Pathology of Domestic Animals.4th edition.Martz, FA, JR Gerrish, RE Morrol>' &PR Peterson. 1993. Macromineral in-take of Polled Hereford cows in fourgrazing systems. 1993 AFGC Proceed-ings, 95-99.Minson DJ. 1990. Forage in RuminantNutrition. Academic Press.Morris JG. 1980. Assessmentofsodiumrequirements of grazing beef cattle: Areview. Journal of Animal Science.50:145-152.SmithGS,KRMiddleton&ASEdmonds.1978. A classification of pOsture andfodder plants according to their ability totranslocate sodium from their roots intoaerial parts. New Zealand Journal ofExperimental Agriculture. 6: 183-188.~(c~Extension Soils Specialist .---COOPERATIVE EXTENSION SERVICEU.S. DEPARTMENT OF AGRICULTUREUNIVERSITV OF KENTUCKYCOLLEGE OF AGRICULTURELEXINGTON. KENTUCKY 40546OFFICIAL BUSINESSPENALTV FOR PRIVATE USE. $300AN EQUAL OPPORTUNITY EMPLOYER, Table 1. Common Grassland Sllecies• Used In Kentucky Agriculture Classified: According to their Na Uptake.BULK RATEPOSTAGE & FEES PAID. USDAPERMIT No. G268Species thataccumulate sodium: Perennial ryegrass• Annual ryegras5, Prairie (rescue) grass: Birdsfoot trefoil· Turnips. kaleWhite cloverOrchardgrassBermudagrassSpecies that do notaccumulate sodiumSorghumTimothyA1sike cloverRed cloverAlfalfaSoybeanMaizeCrabgrass •.,Table 2. TYllical Ranges of Sodium Found in Herbage Dry, Matter.· Plant Species Average Na % DM Range Na % DMAnnual ryegrass 0.11 0.02 10 0.35· Perennial ryegrass 0.42 0.11 10 0.87Orchardgrass 0.51 0.04 to 1.01Timolhy 0.05 om 10 0.19Prairie grass (Malua) 0.14 0.08 10 0.19· Tall fescue 0.29 0.06 to 0.69Bermudagrass 0.03 0.01 10 0.09Sudangrass 0.01 Trace to 0.01Maize 0.03 0.02 to 0.03Alfalfa 0.04 0.02 10 0.08Red clover 0.09 0.02 to 0.16White cloyer 0.11 0.01 to 0.35

Sodium in Pasture Species and Grazing Livestock

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Sodium in Pasture Species and Grazing Livestock

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