SCS-2003-09

Managing Fescue Pasture for HorsesDavid Kee and Byron Housewright*

Texas A&M University

*Assistant Professor and Extension Agronomist, Assistant Professor andAnimal Nutritionist; The Texas A&M University System; Commerce.

“Kentucky-31” tall fescue has been the primary coolseason perennial forage in Northeast Texas andSoutheast Oklahoma since its introduction in the1940’s. Nutritive value and dry matter production datafrom plot studies indicate livestock productivity fromtall fescue can match that seen in other cool seasongrasses. Animal production, however, never matchedthis potential. Fescue foot, summer slump and avariety of other “diseases” have plagued animalsgrazing endophyte-infected tall fescue. Soon, it wasconsidered another poor “Dry Cow” grass; othergrasses were selected to fill the high animalproduction niche. In the 80’s, research at AuburnUniversity associated poor cattle and horseproduction with infestation of fescue with the fungiNeotyphodium coenephialum. The relationship ismutually beneficial one between the grass and thefungus. The relationship benefits the fungus byproviding food, protection and a site for reproductionand benefits the grass by providing protection fromruminant grazing, nematodes, disease, drought andpossible insect attack. Because of this protection,endophyte-infected pastures have improved stand

growth and vigor when compared to endophyte-freefescue pastures.

Fescue toxicosis is caused when animals eat tallfescue infected with the endophyte fungus,Neotyphodium coenephialum. Generally, it does notaffect most fed horses. Infected tall fescue has beenfound to increase the occurance in laminitis in horsesgrazing mature (seedheads present) endophyte-infected tall fescue. Pregnant mares are especiallysensitive to the some of the toxins in infected fescue.Both mare and foal may be affected when the mareeats endophyte-infected fescue. Fescue pasture maylook great, but it is often deceptive. Broodmareconsumption of the endophyte is not the end of theworld. Treatment is available, but prevention is best.

Neotyphodium coenephialum

The endophyte, Neotyphodium coenephialum, growssymbiotically within tall fescue. The endophyte issimilar to ergot fungus found in rye and Dallisgrass.The endophyte grows between the plant cells andoverwinters in the tiller base of the plant. As the plantgrows, the fungus spreads up the plant into theseedhead, increasing toxin concentration ascarbohydrate production by the plant increases. Toxinconcentration is greatest in the seedhead. The

H O R S E S

fungus is spread to uninfected sites through the seed.Plant to plant or field-to-field transmission of theendophyte is very limited.

Fescue Alkaloids and Toxic Effects

The endophyte produces several toxic substances,but the major toxin is ergovaline, an indole alkaloid.The toxins produced by the fungus gives the fescueinsect and disease resistance, suppression of weedseed germination, and reduction in defoliation byanimals. Ergopeptines also have a positive influenceon plant hormones and/or growth regulators. It doeshowever result in livestock toxicity that interferes withprolactin secretion, body temperature regulation, andfeed intake of livestock grazing the infected fescue.Additionally, these alkaloids constrict blood vessels,and reduce blood flow to the extremities. The poorbody temperature regulation and restricted blood flowcauses increased fever and loss of body parts (hoofs,ear tips and tail switches).

Neotyphodium coenephialum produces both lolineand ergopeptine classes of alkaloids. The lolines aresaturated pyrrolizidine alkaloids with mildvasoconstrictive properties. These toxins areassociated with hyperthermia (elevated bodytemperature), fescue foot (gangrene of the feet andtail) observed in cattle and sheep grazing fescue. Theergopeptine class of alkaloids produced byNeotyphodium coenephialum, however was shownin the mid-1980s to be the primary cause of fescuetoxicity. These ergopeptines are primarily ergovaline,ergosine, ergonine, and lysergic acid amine(structurally similar to LSD).

Fescue Toxicosis — Effects on Broodmares

As horses are, unlike other livestock, largelysupplement with grain, the signs of fescue toxicity inhorses are almost exclusively related to poorreproduction. Mares that consume large amounts ofendophyte-infected tall fescue can suffer from anumber of reproductive problems. These can includeprolonged gestation, abortion, premature chorionseparation, dystocia (difficult birth), thickenedplacenta, retained placenta and aglactia (suppressionof lactation, i.e. no milk). Gestation length has beenreported to be extended an additional month in somecases, resulting is severe dystocia and low foalsurvival rates. This dystocia is a result of severalfactors including inadequate preparation of thereproductive tract, as well as increased size of thefoal prepartum and in some cases a rotation of the

foal before birth of 90 to 180 degrees. Additionally,mares that graze endophyte-infected fescue pasturesin early pregnancy may have delayed pregnancy ratesor early embryonic death.

Prolonged Gestation

The normal gestation length in horses isapproximately 11 months, however, mares grazingendophyte-infected fescue can have longerpregnancies (13 months or more). As the fetuscontinues growing during the extra time, dystocia mayresult. These foals may also appear to be immaturedespite their extended fetal development. Largeframe size, poorly developed muscles, overgrownhooves, and premature, irregular erupting baby teethare characteristics of the newborn foal born afterprolonged gestation. New born foals may also exhibithyperthyroidism, poor suckling reflex, incoordination,and low body temperature. Fetal deaths in the lastthird of pregnancy range from 0 to 100%. Becauseendophyte intake can result in aglactia, foals mayalso suffer from starvation, weakness and poorimmunity.

Poor Immunity in Foals

Foals born to mares grazing endophyte-infectedfescue may have reduced immunity, making themhighly susceptible to infections. Normally, foalsreceive colostrum from the mare soon after birth,passing antibodies from the mare to the foal. Mareswith fescue toxicity are often agalactic, their milkproduction, limited or nonexistent. Thus, the newborndoes not consume enough colostrum to receive anadequate amount of antibodies from the mare. Thesefoals are at risk for a number of illnesses andinfections.

If an adequate amount of milk or colostrum is notsupplied to the newborn foal, then the foal should begiven colostrum, from a donor mare, or storedcolostrum from a colostrum bank. Colostrum fromanother species may be used if these options areavailable. Intravenous antibodies and a diet ofsupplemental milk should follow. Sugar spiked cowor goat milk may be used. The sugar is added tomake the solution more closely resemble mare’s milk.

Treatment of Fescue Toxicity

The best form of treating fescue toxicosis in horsesis prevention. If this is not possible, supplementednon-pregnant horses can safely graze on vegetative

(no seedheads) endophyte-infected fescue pastures,as can broodmares during the second trimester ofpregnancy. If a pregnant horse must graze onendophyte-infected fescue, drugs are available tohelp reduce the adverse effects. These includedomperidone (prevents ergovaline from inhibitingprolactin release, thus prevents aglactia),perhenazine and reserpine. The best methods ofpreventing or coping with fescue toxicosis involve thefollowing principles: eradication of the endophyte;diluting the endophyte; and avoiding to the endophyte.

Prevention

The endophyte can be eradicated by killing infectedstands of tall fescue with by replanting with othergrasses. Mechanical control can be achieved bymultiple mowing in May and June, followed by diskingin July. This will, however, provide a respectableseedbed for the previously produced endophyteinfected seed. A one to three year period is requiredto eradicate infected tall fescue from a pasture. Twoherbicides are effective for fescue control. Roundupshould be applied at 1 pint/acre 2-3 times in May toearly June, the pasture disked and planted to a warmseason annual, escape fescue should be killed withadditional Roundup or Gramoxone (applied at 1 pint/acre in two applications two weeks apart inSeptember), the site disked and planted to a coolseason annual, or held fallow, then disked and plantedto a warm season perennial in the following spring.A non-infected fescue variety may also be used.However, because non-infected fescue is not ashardy as endophyte-infected varieties, a commitmentto improved grazing and forage management mustbe made.

A new technology has been recently developed.Novell-endophyte fescue (MaxQ) fescue is marketedby Pennington seeds. Other companies areanticipated to be releasing similar technology in thenear future. This plant is infected with one of theNeotyphodium coenephialum strains, but this specificendophyte does not produce the mammalian toxin.Results from Mississippi and other states have shownno negative animal (equine, bovine or ovine speciestested) responses have been associated with grazingof this product by several classes of livestock(growing, mature and pregnant). Livestock gainshave been much greater than from endophyte-infected fescue compared to endophyte-infectedfescue, and statistically similar to that from endophytefree fescue.

Interseeding or overseeding legumes into fescuestands increases the protein content and energyconcentration of the pasture’s forage, while dilutingthe amount of endophyte consumed daily. Whiteclover, alfalfa and annual lespedeza have all beenused successfully in the southwest. Legumes canbe seeded with a no-till drill or broadcast with orwithout harrowing. The best method of plantingdepends on the legume used and the time of yearwhen planted.

Grain supplementation also acts to dilute the amountof endophyte consumed. A South Carolina study hasshown that supplemented young growing horses didnot exhibit the effects normally associated withconsuming infected fescue. However, pregnantmares were negatively affected by consuminginfected tall fescue, regardless of supplementationlevel.

The effects of the endophyte can be minimized byonly grazing infected stands in the fall through earlyspring when fescue nutritive value is high andendophyte effects are the lowest. Broodmares shouldnot graze infect fescue in the last trimester ofpregnancy and several months following foaling.Mare’s recovery, once removed from infected fescueis very rapid and producers should notice normallactation, parturition and foal behavior. Reducing oreliminating spring (January to mid June) nitrogenfertilizer will suppress the quantity and quality offescue seed, seedheads and tillers produced in thespring. This, in turn, reduces toxin content in thefescue. During the summer months, other grass orgrass-legume pastures should be grazed. The fungustends to concentrate in the stem and seedhead. Ifplants can be kept young and vegetative by grazing(or mowing) practices that keep stands from maturing,the effect of the endophyte on performance isdecreased. Similarly, if fescue hay is cut in the bootstage (just before the seedhead emerges),performance in animals eating the hay is improvedover those that consume late-cut hay.

For additional information please visit the followingwebsites:

http://soilcrop.tamu.eduhttp://foragesoftexas.tamu.edu

http://tcebookstore.org

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with theunderstanding that no discrimination is intended and no endorsement by Texas Cooperative Extension, or the Texas A&M Univer-sity System is implied.

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Soil & Crop Sciences DepartmentTexas A&M University

College Station, TX77843-2474

Educational programs of Texas Cooperative Extension are open to all people without regard to race, color, sex, disability, religion, age, or nationalorigin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30,1914, in cooperation with the United States Department of Agriculture. Chester P. Fehlis, Deputy Director, Texas Cooperative Extension, The TexasA&M University System.