Research Information Sheet #104 August 2001 · Internal Parasites of Cattle in Louisiana and Other...

Internal Parasites of Cattle in Louisiana and Other Southern States 1

Research Information Sheet #104 August 2001

Introduction....................................................................................................................... 2The Parasites .................................................................................................................... 3Harmful Effects of Internal Parasites in a Cattle Herd .......................................................... 5Recognition of Internal Parasites as a Problem in a Herd .................................................... 7Transmission of Parasite Infections to Cattle ....................................................................... 8Inhibition of Larval Development - Ostertagia Ostertagi ..................................................... 10Prevention and Control of Internal Parasites ................................................................... 11Grazing Management ...................................................................................................... 11Use of De-wormers in Control .......................................................................................... 12Systematic or Strategic Use of De-wormers ...................................................................... 13Improved Cattle Resistance to Parasites Through Management and De-wormers ............... 14Drug Resistance in Cattle Nematodes .............................................................................. 15Treatment Recommendations .......................................................................................... 16

INTERNAL PARASITES OF CATTLEIN LOUISIANA AND OTHER SOUTHERN STATES

J.C. Williams and A.F. Loyacano

INTERNAL PARASITES OF CATTLEIN LOUISIANA AND OTHER SOUTHERN STATES

2 Internal Parasites of Cattle in Louisiana and Other Southern States

Cattle of all ages, but particularlyyoung cattle, are affected by adiversity of internal parasites. Amongthese are the roundworms (Nema-todes), which are primarily parasitesof the gastrointestinal tract (a lung-worm is included), the liver fluke(Trematodes), tapeworms (Cestodes)in the small intestine, and single-celled protozoan parasites (Coccidia)in the lower intestinal tract. Climaticconditions through most of thesouthern region of the U.S., includ-ing Louisiana, provide for longgrazing seasons; however, these sameconditions provide an ideal settingfor internal parasites. Periods ofgreatest infection risk occur fromlate winter through spring and againin the fall. Considerable infectionmay also occur during milder wintersand during summers that are verywet and not overly hot. Underpasture conditions, it is the rule toencounter mixed infections withseveral types of roundworms as wellas with other parasites indicatedabove. Because of their wide distri-bution throughout the southernregion, the large numbers of cattleinfected, and the damage caused bythe worms, nematodes are consid-ered to be the most economicallyimportant group of internal parasitesin cattle.

The progressive cattle producertoday generally has a high level ofunderstanding of factors that can cutinto efficiency and profits in produc-tion. In spite of this, there are manywho still underestimate or ignore theeffects of internal parasites on cattleproductivity and health. Undercertain conditions of management,such as with low stocking densitiesand high levels of nutrition, it isoften difficult to demonstrate thatcontrol methods for internal para-sites are warranted. However, undermost circumstances, in which cattle

production in the South is highlyintensified and internal parasites arepresent in an environment that ishighly favorable to their propaga-tion, it is likely that productivity canbe enhanced or substantially im-proved by parasite control measures.

Determination of accurateestimates of production losses tocattle internal parasites is difficult toachieve. Illness and deaths areobvious, but effects on weight gain,feed conversion, reproductive perfor-mance, cost of drugs and othermedications, and other factors aremore complex to assess. At variedintervals, national estimates of loss tointernal parasites, external parasitesor other disease entities are issued bygovernmental and other agencies.For records of 1994-1995, therewere 103.8 million cattle in theUnited States valued at $66.5 billion(Agricultural Statistics, USDA,1996). American pharmaceuticalcompanies estimated that gas-

TABLE 1. Weight gains (lb.) of cattle treated with different anthelminticscompared to untreated control cattle

Example 1. Treatment least square means for body weight (lb.) of cattle treated onstudy days 0 (Jan 11) and 84 (Apr 5)

Treatment - All Study DayGroups n =18/gp 0 28 56 84 112 140 160

Untreated controls 477ab 486a 508a 539a 592a 638a 689a

Doramectin inject. 469a 521b 574b 631b 730c 777c 818c

Ivermectin inject. 482b 526b 570b 620b 713b 759b 807b

Ivermectin pour-on 466a 515b 563b 623b 702b 757b 796b

Different superscript letters in columns indicate significant differences (P<0.05).

Example 2. Bodyweights (lb) of untreated control cattle and cattle treated with apour-on endectocide on study day 0 (Jan 18)

Treatment – All Study Day Total Value @ Value/Groups n=15/gp 0 28 56 84 112 gain $.7135 control

Untreated controls 481a 557a 638a 719a 762a 281 543.69 —Doramectin 484a 587b 683 bc 764bc 807bc 323 575.79 32.10Ivermectin 481a 582b 668b 744ab 788ab 307 562.24 18.55Eprinomectin 485a 586b 685 bc 765 bc 812 bc 327 579.36 35.67Moxidectin 485a 593b 696c 778c 823c 338 587.21 44.52

Different superscript letters in columns indicate significant differences (P<0.05).

trointestinal parasites can cost theproducer from $25 to $200 peranimal (Smith Kline BeechamAnimal Health, 1991). Even at thelower estimate, this translates into a$2.5 billion loss to the cattle indus-try each year. Obviously, all 90million to 100 million cattle in agiven year are not treated, but thefact that some may be treated morethan once per year likely balances outthe estimated numbers.

Two examples of how anthel-mintic treatments can favorablyaffect weight gains in stocker beefcattle in comparison with untreatedcontrol calves are shown in Table 1.In all cases, the effect of treatmentby far exceeds the cost of treatments.Such results have been observedinvariably with different anthel-mintics in the two examples and inmany other LSU Agricultural Centerresearch studies. It should be re-membered, however, that eventhough anthelmintics are indispens-

Introduction



able in parasite control, other factors,such as a good nutritional level andgeneral management, are also indis-pensable. When control of gas-trointestinal nematodes and lung-worm is combined with a plannedand systematic effort to simulta-neously control the liver fluke (whereapplicable) and ectoparasites, (i.e.,flies, lice, grubs, etc.), productivitywill be increased. Good control ofany of the parasite groups justindicated can result in increasedproductivity, depending on preva-lence in a given geographic area;however, good control of all para-sites along with good overall herdhealth is the best guarantee ofincreased productivity.

Figure 1. Ostertagia ostertagi: The medium stomach worm ofcattle. (A) Adult male parasite, approximately ½ inch long and early4th-stage larva, less than 1/16 inch long. (B) Yearling calf with severeOstertagia infection – note rough hair coat and bottle jaw. (C) Calfwith similar condition in chute – note severe diarrhea. (D) Calfabomasum showing “Morocco leather” appearance due to heavyOstertagia infection.

The Parasites

Several genera and species ofnematodes are commonly found incattle of all ages in the southernregion. As pointed out earlier, thenematodes are the most commonand numerous of the internal para-sites of cattle in the southern regionand, consequently, more of a threatfor disease and production loss thanother internal parasites. Largestinfections are usually found inweanling and yearling cattle. Theworms are parasitic in differentportions of the gastrointestinal tract.The abomasum or true stomach isthe site of Ostertagia ostertagi, the

brown or medium stomach worm,considered to be the most harmfuland economically important parasiteof cattle in temperate areas of theworld (Figure 1). More will be saidlater about a seasonal variation indevelopment of this parasite that canresult in severe parasitic problems.Also present in the abomasum areTrichostrongylus axei, the stomachhairworm, and Haemonchus sp., thelarge stomach worm or barber poleworm.

Among worms in the intestinaltract are several species of Cooperia,Strongyloides papillosus, Trichos-


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trongylus colubriformis, Nematodirushelvetianus, Bunostomumphlebotomum, the hookworm,Oesophagostomum radiatum, thenodular worm, and Trichuris sp., thewhipworm. The cattle lungworm,Dictyocaulus viviparus, is found inthe large and small air passages ofthe lungs. It is the only lungwormcommonly found in cattle. The liverfluke (Fasciola hepatica) occurs inthe liver tissue (larvae) and bile ducts(adults). Nearly all of the worms arerather small and delicate, rangingfrom a fraction of an inch to morethan an inch in length. In contrast,tapeworms of cattle (Moniezia spp.)can grow to very large size in the

Figure 2. Damage caused by gastrointestinal nematodes in cattle:(A) Hemorrhage caused by large stomach worm Haemonchus. (B)Less obvious reddened areas due to smallest of the cattle stomachworms – Trichostrongylus axei. (C) Section of duodenal/upper

intestinal tissue showing some slight hemorrhagic condition andthickening of mucosa as caused by Cooperia spp. (D) Lower smallintestine showing nodules caused by larvae of the nodular worm –Oesophagostomum.

small intestine but are not known tocause any ill effects.

The prevalence of nematodeinfections in cattle throughout theregion is high. Surveys and otherstudies of apparently healthy cattle(beef and dairy cows, yearling steers,replacement heifers, and calves)generally reveal infection levels of80% and greater as indicated by fecalegg counts and post-mortem exami-nation. As mentioned earlier, level ofparasitism is greatest in young cattle;adult beef and dairy cattle generallyshow little evidence of nematodeinfection or disease unless stressed bynutritional deficiency or otherdiseases.


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loss of serum albumin from theblood, reduced acidity, and severediarrhea. The large stomach worm(Haemonchus) is an avid bloodsucker as is the intestinal hookworm,Bunostomum. Worms in the intesti-nal tract (Cooperia, Trichostrongylus,Nematodirus) can all cause damageto the intestinal lining when presentin large numbers. The lungworm cancause severe disease and deathsprimarily from the effects of pneu-monia and asphyxiation. Livercondemnation is a major loss causedby damage due to the liver fluke.Besides anemia, serious productionlosses can be attributed to the fluke

Harmful Effects ofInternal Parasites in a

Cattle Herd

The means by which nematodesinflict damage on the host andconsequently cause disease andreduced productivity are not wellunderstood. Different nematodesmay penetrate and migrate in tissue,suck blood, or otherwise cause smallhemorrhages, cause erosion ofsurface layers of the gut lining, orincite formation of nodules. Themedium stomach worm (Ostertagia)can extensively destroy vital digestivecells of the abomasum, resulting in

Figure 3. Further examples of damage caused by parasites incattle: (A) Section of mid intestinal region showing some areas ofthickening and hemorrhage as caused by the hookwormBunostomum and other worm species. (B) Cut section of livershowing opened bile duct region with flukes present. (C) Yearling

calf with severe lungworm infection – note head down, tongue outand animal “gasping” for breath. (D) Cut section of lung showingmass of thread-like lungworms and yellow host exudate. Notelighter normal tissue in contrast to deeper red areas in lung tissueand purplish color on lung outer surface.

for reasons not clearly defined. Sincemany of the different types of wormsmay occur in cattle at the same time,their individual and collective dam-aging effects are not difficult tocomprehend (Figure 2, Figure 3).

For a long time it was thoughtthat the primary effect of nematodeinfection on the host was interfer-ence with digestion and malabsorp-tion of nutrients. Considering thebasic digestive and absorptive func-tion of the gut and the mechanicaland possible chemical damageinflicted by parasites, the associationappeared to be appropriate. Recentevidence has shown that damage and


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inflammation of the lining tissue ofthe gastrointestinal tract results inleakage and loss of blood proteininto the gut. Such loss can drasticallyalter protein metabolism, includingmuscle growth. A major unexplainedeffect of infection is loss of appetite.The end result is failure to grow orweight loss (Figure 4). For a numberof years in parasite control studies atthe Dean Lee Research Station nearAlexandria, it has been observed thatcattle treated experimentally forparasites graze their pastures more

Figure 4. (A) Weaner/yearling cattle during a wet and coldLouisiana winter. Note poor condition, evidence of diarrhea due toparasitism. (B) Abomasa from calves of different treatments in aparasite control field study – abomasum at right end is from anuntreated control; the abomasum at left end is from group thatreceived maximal control and grazed on pasture with little infection;the abomasum in center is from a calf that received maximal

control but grazed on pasture with heavy infection risk. Levamisoleand thiabendazole were drugs used in this 1982 study, but themajor point is effect of pasture management in reducing infectionrisk. (C, D) Comparison of a severely parasitized abomasum(Ostertagia) on left and another from a calf on the right of similarage (early yearling) but not exposed to infection.

completely than untreated controls.The aerial photograph shown inFigure 5 demonstrates this differencein pastures. The differences inappearance are due to forage heightand availability because of decreasedappetite in untreated control cattle.At relatively high stocking rates,treated animals may graze pasturesso close that they do not havesufficient forage for optimum weightgain. Animals not treated, on theother hand, may have significantlymore available forage and, even

though they need less forage, theyhave all they want and can reachtheir performance potential. This canmask some of the differences be-tween treated and non-treatedanimals. Nematode infections, aswell as factors such as forage palat-ability and toxicity, can also biasforage evaluation studies by affectingforage availability and nutritivevalue. Replicates of different stock-ing rates may be necessary to accu-rately evaluate differences.


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Recognitionof Internal Parasites

as a Problem in a Herd

Figure 5. Aerial photograph of pasture at the Dean Lee Research Station showing effect oftreatment for parasite control on appetite in cattle. The four pastures (5 cattle on each 4-acre plot) separated by vertical lines are those of note; pasture on far left is wedge-shaped.Differences in appearance are due to forage height and availability because of decreasedappetite of untreated and parasitized control animals. Pastures occupied by treated animalsare lighter in color, while the control pastures are darker green, indicating a greater amountand density of forage.

diseases. The producer who sees hiscattle regularly can often judgewhether such problems exist.

Besides early recognition ofparasitism, which can help in reduc-ing further loss and preventingcontinued contamination of pasturewith worm eggs, an evaluation ofgeneral management, grazinghistory, and weather factors isimportant in determining risk ofparasitic infection. Nematode para-sitism is closely associated withcertain grazing practices, and avoid-ing or altering these practices canreduce risk. Temperature and rainfallare also clearly related to the dangerof parasitic infection under certaingrazing practices. Services of aveterinarian are often required tofully understand the nature of agiven problem and to achieve asolution. An experienced herd healthpractitioner can aid producers by

evaluating all factors involved,including clinical signs of parasitism,differentiation of parasitism fromother disorders/diseases, deficientnutrition, and the relationship ofmanagement and weather factors.

Two techniques that a veterinar-ian may use to help in diagnosis arefecal examination for parasite eggsand post-mortem examination.Microscopic examination of cattlefeces for parasite eggs can indicatewhat worms are present and may atleast suggest levels of parasitism. Thepost-mortem examination of ananimal or animals in a herd that dieis the most direct method of deter-mining the kinds of worms presentand the amount of damage caused.Observations of the producer andveterinarian in many herds willindicate that worms are a significantburden even though a post-mortemexamination is not feasible or incon-

While all cattle can be expectedto have some nematodes in theirgastrointestinal tract, it should notbe assumed that all or most cattle areadversely affected by clinical parasit-ism. Clinical parasitic disease isusually obvious; minimal or not sominimal losses in day-to-day produc-tivity caused by small worm burdensare not so obvious. Loss in produc-tivity due to inapparent or subclinicalparasitism has not been accuratelyassessed, but most evidence indicatesthat it results in greater lossesindustrywide than clinical diseaseoutbreaks. It might be noted thatwidespread use of the avermectin/milbemycin compounds (ivermectin,doramectin, eprinomectin, andmoxidectin), with their highlyefficient anthelmintic activity andpersistence, has generally reducedthe occurrence of acute parasiticdisease outbreaks.

Recognition of nematode para-sitism, whether it be a clinical diseaseoutbreak or subclinical inapparentparasitism and reduced productivityin a herd, is a key factor in anyapproach to prevention and control(Figure 6). The classical signs ofsevere parasitism such as progressiveweight loss, diarrhea, rough haircoat, bottle jaw, and anemia are alltoo familiar. In many cases, however,it is necessary to rule out the possi-bility of diseases other than parasit-ism or deficient nutrition. Effects ofroundworm parasites in a herd maygo largely unnoticed except withcareful observation. Such effects mayinclude inefficient feed utilization,delay in attainment of breeding age(puberty), poor conception rates/pregnancy, depressed milk produc-tion, and lighter calves with greatersusceptibility to parasitism and other


clusive and worm egg counts arelow. “Diagnostic treatment” in suchcases with an efficient de-wormer oranthelmintic can help to understandand alleviate the problem andultimately improve overall herdperformance.

Figure 6. Cattle nematode parasite eggs and infective larvae. (A) Microscope illustration ofa gastrointestinal nematode egg from fecal sample (large object at right center) and to thelower left is a protozoan oocyst (coccidia). (B) The picture is “staged” but shows a largenumber of cattle nematode infective larvae in a droplet of water on a blade of grass – thishappens in nature.

Transmission of ParasiteInfections to Cattle

Adult male and female worms ofthe various nematode genera inhabitdifferent parts of the gastrointestinaltract. After mating, female wormsproduce eggs that are passed out infeces onto the pasture. In the case ofthe lungworm, eggs hatch in thegut, and first-stage larvae are passedin the feces. Hatching of eggs anddevelopment and survival of infectivelarvae are highly dependent ontemperature and moisture. Allprocesses are rapid in warm weatherand slowed during cooler weather.High temperature and desiccation insummer and subfreezing tempera-ture in winter can effectively kill offeggs and larvae on pasture, and thisoften results in reduced parasitetransmission during these periods. Inaddition, hot and alternating wetand dry periods of summer in theregion are more adverse to nematodefree-living stages on pasture thanwinter conditions. The basic lifecycle of the nematode parasites fromthe time that eggs are deposited infeces on pasture until infective larvaeare available for infection and theparasitic stage in cattle is shown inFigure 7.

Infective larvae of most nema-tode species on pasture grass areswallowed with forage by grazingcattle. In the case of the hookworm,Bunostomum, and the intestinalthreadworm, Stronglyoides, infectionoccurs when infective larvae pen-etrate the skin of cattle. This occurson the lower portion of the legswhile animals stand in muddy, fecal-contaminated areas or anywhere onthe body surface when animals liedown in such areas. Larvae of thelatter two worms travel by the bloodto the heart and lungs and then tothe intestinal tract where theymature. In the case of the cattlelungworm, eggs hatch in the cattle

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Figure 7(A). Life cycle of gastrointestinal nematodes in cattle. Generalcycle of nematodes of the stomach and intestinal tract. Developmentaltime in cattle ranges from 2-5 weeks for most, but up to 8-9 weeks forthe hookworm.

intestine and early or first stage larvae arepassed in the feces. Development ofgastrointestinal nematode larvae to thethird or infective stage can occur as quicklyas 7 to 14 days on pasture during optimalconditions (warm weather) but may bedelayed for several weeks in colder weather.Once larvae reach the infective stage theycan survive for several months from falland winter to spring. This fact clearlyemphasizes how large levels of pasturecontamination accumulate under poor andsometimes generally good managementconditions. Survival is generally shortestduring summer.

After infection of cattle, most of thenematode parasites develop to the adultstage in 2 to 4 weeks. Major damage in theabomasum and intestinal tract occursduring the period of larval development tothe adult stage. Therefore, with a total lifecycle, from egg to egg, requiring about 6to 8 weeks (2 to 3 weeks on pasture and 2to 5 weeks in the cow) during much of theyear, it is possible for infections to recycleseveral times during a long grazing season.With constant daily infection occurring ingrazing cattle during a grazing season,considerable worm burdens can develop.

The life cycle of the liver fluke is farmore complicated than the direct cycle ofnematodes. Development of the liver flukein the free-living environment requires anintermediate host (snail), and the free-living phase requires 10 to 12 weeks beforeinfection can occur. The parasitic phasealso requires about 10 to 12 weeks, fromtime of infection to development of matureparasites (Figure 8). In Louisiana, Texas,and Florida, most fluke transmissionoccurs between the months of Februaryand July. Moisture surplus and tempera-tures during this period are most suitablefor expansion of snail populations anddevelopment of immature fluke stages onpasture. Fluke transmission effectivelyceases during the drier months of summerand early fall. By fall, fluke infections incattle consist almost entirely of matureadults and, consequently, treatment is mosteffective at this time.

Figure 8. Life cycle of Fasciola hepatica, the common liver fluke incattle.

Figure 7(B). Life cycle of gastrointestinal nematodes in cattle. Life cycleof Ostertagia ostertagi, including notes on the inhibited larval phasethat occurs in spring and summer in Louisiana.



Inhibition of LarvalDevelopment - Ostertagia

Ostertagi

Throughout the southernregion, including Louisiana, themedium stomach worm presents anadditional problem, making itunique from the other gastrointesti-nal nematodes because of a seasonalvariation in its life cycle pattern.Weather conditions from late springthrough early fall are adverse tosurvival of infective larvae of thisparasite on pasture and, conse-quently, little or no infection withthis parasite occurs during theperiod. However, the parasitepopulation does not die off butspends the period of adverse weatherin an inhibited or arrested early (L4)larval stage in tissues of the cow’sstomach (Figures 7B and 9). TheOstertagia infection and diseasepattern is closely tied in with ageclasses of cattle and different seasons.

During late fall through winterand particularly in early spring, cattlenear weaning age and up to 14 to 16months of age can be affected byType I Ostertagia disease. This is atime of year that is basically optimalfor development and survival ofinfective larvae on pasture. Wheninfection occurs, the worms developpromptly to the adult stage in thenormal time span of about 3 weeks.With heavy infection, the youngcattle can be severely affected,showing substantial weight loss. It isalso during spring that most of theOstertagia larvae on pasture becomeconditioned by weather factors toundergo inhibition of developmentonce swallowed by the cow. Thisprocess presumably occurs in theseveral weeks preceding the onset ofhot and dry or wet weather ofsummer that kills off larvae onpasture. During the inhibited state(Pre-type II Ostertagia), the larval

usual to see the condition in oldercows and bulls as well. Large num-bers of inhibited larvae, accumulatedin stomach tissue during spring, canmature at intervals in the fall, caus-ing a long and drawn out diseaseprocess that may result in death.

In northern portions of theUnited States, the inhibition patternof Ostertagia ostertagi is different.Larvae become inhibited in develop-ment during late fall grazing andremain in the stomach tissuethrough winter (Figure 10). As aresult, Type II disease occurs fromlate winter into spring, and Type Idisease in younger cattle occursduring summer and fall. In theabsence of documented research, thetype of Ostertagia pattern that existsin various parts of the country

Figure 9. Seasonal pattern of infection risk for gastrointestinal nematodes and lungworm inLouisiana and other warm temperate regions. Major infection risk occurs from late winterinto spring, having remained lower or even increased during winter, following lowest levelsduring summer and early fall. In the case of the stomach worm, Ostertagia ostertagi, adultworms predominate in winter and again in the fall, but numbers of inhibited early 4 th- stagelarvae increase in numbers during spring and remain in glands of the abomasum until theymature to adults in the fall.

worms cause no problems. However,the inhibited worms will begin tomature to adults usually in lateAugust and September, a time whensummer temperatures begin todecrease. In the maturation process,the worms increase in size abouttenfold in a relatively short time,causing massive destruction ofdigestive tissue of the stomach. Thisform of Ostertagia disease is calledType II Ostertagia disease; itsharmful effect is similar to but farmore serious than Type I disease.Type II disease is seen most com-monly from August to October, andusually only a small portion of a herdis severely affected. Yearling steersolder than 16 months of age andreplacement heifers of similar age arecommonly involved. It is not un-



Figure 10. Seasonal pattern of infection risk for gastrointestinal nematodes and lungwormin cool temperate regions of the United States. In contrast to Louisiana and similar climaticregions, the seasonal pattern of infection risk is different. Reflecting the effects of winter/snow cover in cool temperate regions, parasite infection is of no significance. However, atthe time that cattle are initially turned out to pasture in spring, a small initial rise in infectionmay be due to infective larvae that have overwintered on pasture. Major time of infectionrisk begins in mid- to late summer and extends into fall. In the case of Ostertagia ostertagi,inhibited early 4 th-stage larvae are acquired during late fall and mature to adults in thefollowing spring.

remains unknown. In areas such asthe central plains and in states acrossthe center of the country from theMississippi River to the Atlantic, thetime and duration of larval inhibitionand disease types have not beendefined.

A problem in the past has beenthat older anthelmintics such asthiabendazole and levamisole wereeffective against adult worms but notagainst inhibited larvae of themedium stomach worm. These drugswere effective in controlling Type IOstertagia in winter and spring butineffective in killing inhibited larvaeand controlling Type II Ostertagia.New and improved anthelminticsare effective against inhibited larvaeand will be discussed in a latersection.

Prevention and Controlof Internal Parasites

Eradication of worms is virtuallyimpossible, but control of wormsmust be a major component of cattleherd health programs, particularly inthe South. The major aim of effec-tive parasite control is to keepinfections as low as possible tominimize any interference withproduction.

Effective control must be lookedupon not as a single approach but asan integration of different compli-mentary components. In broadoutline, these components in controlsystems are grazing management,use of efficient de-wormers, andenhancing the capability of cattle toresist infection.

Internal Parasites of Cattle in

Grazing Management

Prevention of parasitism isseldom planned into grazing man-agement; however, grazing practicescan affect pasture contaminationlevels and risk of infection. Pasturesconsidered to have lowest levels ofparasite contamination should bereserved for younger, most suscep-tible stock (weaners, stockers,replacement heifers). Reducedpasture contamination (safe pasture)can result from the following prac-tices: pasture vacated for severalweeks in summer for hay production,pasture grazed exclusively by olderdry cows (they produce far lesscontamination than younger cattle)for several weeks, harvested croplandor rested pasture planted in annualforages, and frequent, but expensive,treatment with de-wormers. The lastmentioned means could never berecommended because of ineffi-ciency, expense, and the potential ofinducing drug resistance. Sinceyounger stock generally have highestlevels of infection and produce heavypasture contamination, one group ofyoung stock should not followanother such group on the samepasture.

A frequently asked questionconcerns the use of pasture rotationin parasite control. The truth of thematter is that regular rotationpractice in no way reduces infectionrisk but may increase the risk. A 3-to4-week rotation allows time for eggsdeposited on the pasture during theprevious rotation to hatch anddevelop into infective larvae at aboutthe same time that cattle are reintro-duced to the pasture. Abundant,growing forage provides protectionfor the larvae from weather factors.Cattle in short-duration, rotationalgrazing programs (2- to 4-daypasture rotation) may consume ahigh percentage of the availablelarvae.


Use of De-wormers in Control

Development of highly efficient, broad-spectrum de-wormers since theearly 1960s has been of untold benefit in reducing losses to nematode parasit-ism in cattle. General characteristics of all major products available to produc-ers since that time are given below:

into only sparing use: moranteltartrate-(Pfizer), levamisole (FortDodge). Decline of these productscannot be definitively attributed todrug resistance in cattle nematodes,although activity against specificparasites (Ostertagia) decreased overtime. These compounds were essen-tially replaced by benzimidazoledrugs (related to thiabendazole),released for use in the United Statesfrom the late 1970s into the 1980s,namely Safeguard, fenbendazole(Intervet); Valbazen, albendazole(Pfizer); and Synanthic, oxfendazole(Fort Dodge). These products wereused extensively for a decade or twoand were highly active againstgastrointestinal nematodes andlungworm. There was some activityagainst the tapeworm (Moniezia),and albendazole offers some aid incontrol of the liver fluke (Fasciola).All three of the benzimidazolecompounds just mentioned are stillwidely used by cattlemen, all retaingood activity against a broad spec-trum of parasites, but all three have acommon fault of variable efficacy a-gainst inhibited larvae of Ostertagia.

Beginning in 1984, a newchemical class of de-wormers wasintroduced beginning withivermectin. While de-wormingproducts were always termedanthelmintics, meaning they killedworms, the new generation com-pounds were termed endectocides,meaning they had powerful activityagainst both “endo” (internalparasites) and “ecto” or externalparasites (lice, flies, ticks, mites,grubs). These products do not haveactivity against liver flukes or tape-worms. Since the development andrelease of ivermectin (Ivomec) byMerial in 1984, two other similarproducts were made available for usein 1996 (Dectomax, Pfizer) and1998 (Cydectin, Ford Dodge),respectively. Additionally, in 1997,Merial introduced an exclusively

Persistence of effective drugactivity of single doses ofivermectin, eprinomectin, dora-mectin, moxidectin will rangefrom approximately 3 to 6 weeks.

very effective and, in some cases,were as harmful to the host animal asto the parasites. Some of the com-pounds introduced from the early1960s were highly useful and effec-tive in their time, but either they areno longer manufactured (thiabenda-zole-Merck/Merial) or have fallen

Early Modern AnthelminticsThiabendazole – Merial no longer makes the productLevamisole, Tramisol – still available, various formulationsMorantel tartrate, Rumatel – in-feed formulations

Benzimidazole AnthelminticsFenbendazole, Safeguard, Panacur, (Intervet) oral, block, and

in-feed formulationsAlbendazole, Valbazen (Pfizer) oral, in-feed formulationsOxfendazole, Synanthic (Fort Dodge) intra-ruminal injection, oral

Besides efficacy against nematodes, all the benzimidazole drugs havesome effect against tapeworms; albendazole provides “aids in control”for liver fluke. Fenbendazole is also available for use in lactating dairycattle of breeding age. Slaughter withdrawal times for fenbendazole,albendazole, and oxfendazole are: 8 days (oral) and 11 to 13 days (infeed), 27 days and 7 days, respectively. The effective worm killingduration of these drugs is 2 to 3 days. The only drug available forfluke control is clorsulon, Curatrem (Merial).

Endectocidal Products for Endo- and EctoparasitesIvermectin, Ivomec (Merial) from 1984, injectable, pour-on, 35- and

48-day slaughter withdrawal, respectivelyIvomec-F or Plus (+Curatrem), efficacy against nematodes, adult liver

flukes, and external parasites. Slaughter withdrawal time of 49 daysand not for use in dairy animals of breeding age

Ivermectin Sustained-Release (SR) Bolus (Merial), from 1997,prevents infection up to 5 months after single treatment; 180-dayslaughter withdrawal time; not for use in dairy animals of breeding age

Eprinomectin, Eprinex (Merial), from 1997, pour-on only, no meat ormilk withdrawal

Doramectin, Dectomax (Pfizer), from 1996, injectable and pour-on,not for use in dairy animals of breeding age and slaughter withdrawaltime of 35 days for injectable and 45 days for pour-on

Moxidectin, Cydectin (Fort Dodge), from 1998, pour-on only, no meator milk withdrawal

Prior to 1960, drugs available forparasite treatment were generally not



pour-on product called Eprinex(eprinomectin), which is related toivermectin but has no meat or milkwithdrawal period and is approvedfor dairy cattle. Merial also in 1997introduced its ivermectin sustained-release bolus (SRB), which canprevent infection with nematodes forup to 5 months. While the olderproducts were purely synthesizedchemicals, the new generation,endectocidal compounds have beenderived from bacterial/fungalorganisms by fermentation andfurther manipulated chemically. Amajor characteristic and advantage ofthe new generation products overolder ones is persistence of anti-parasitic activity. While killing actionof the benzimidazoles (fenbenda-zole, etc.) extends maximally forabout 3 days, activity of the mostcurrent products may extend from 3to 6 weeks, and as noted for theivermectin SRB, up to 5 months.This is a major advance in efficiencyof a single treatment, that is inpreventing pasture contamination,particularly when coupled with somegrazing management procedure tofurther limit reinfection.

The modern de-wormer prod-ucts, especially the newer generationof endectocidal compounds, are wellsuited for timely strategic treatmentsbased on their overall high efficacyand killing activity, which lasts for 3to 6 weeks. In some instances, asingle treatment with these productsis fine. In most cases, however, atleast two treatments, spaced approxi-mately 8 to 12 weeks apart, forexample for stocker calves grazing onwinter pasture, is recommended. Theivermectin SRB, which costs ap-proximately three times as much as asingle treatment with ivermectininjectable or pour-on, is capable ofprotecting cattle from infectioncompletely during the southernwinter-spring grazing season.

Systematic or StrategicUse of De-wormers

Inspite of all of the advances inevolution of anthelmintic technol-ogy, there has remained a largetendency among producers toconsider de-wormers as the sole ormajor means of control, sometimesto the exclusion of overall goodmanagement and constant provisionof good nutrition. To some extentthis policy has been fueled by thoseselling de-wormer products, withlittle concern being given to timingof treatments and other means ofreducing infection risk in specificgeographic regions. The primarypurpose of de-wormers is not tocure sick animals, whether mildlyor severely ill, but to reduce levels ofpasture contamination and conse-quently prevent such episodes ofillness or reduced productivity.Reducing pasture contaminationwith eggs/larvae is most effectivelyaccomplished by some systematictiming or strategic use of de-worm-ers, tied in with management, such

as a comprehensive herd healthprogram. It is essential when infor-mation is available that treatmenttiming be meshed in with seasonalprevalence of infection risk. Withirregular treatment, or at times whenthe herd or individuals in the herdlook like they need treatment, it isalready too late. This essentially is awaste of time, labor, and cost of thedrug and only serves to preventdeaths or further deterioration ofcattle condition.

The advantage of systemic use ofde-wormers or strategic treatment isthat it can be timed to mesh withsome management procedure such aschange of pasture. Also, de-wormingmight be done at the beginning of aperiod such as summer, when hotand dry weather is most destructiveto eggs/larvae on pasture. The de-wormer, along with managementand weather, can be very efficient incutting down losses to parasitism.The widely used spring and falltreatment has much merit in that itremoves the large worm loads thatcan be acquired at these times and

Parasite control study with cow/calf herd on rolling pastures at the Hill Farm ResearchStation, Homer, Louisiana.


delays and reduces pasture contami-nation. Treatment of all cattle a dayor two before going to pasture oflow infection risk is a must. Treat-ment at any time of year is mosteffective when the cattle do notreturn to heavily contaminatedpasture and rapid reinfection. Itshould be remembered that althoughthe newer endectocides have ex-tended or persistent activity, they arenot like vaccines with unlimitedprotection time.

One can make decisions as topriorities on what product to useunder different circumstances, that isroutine use of the best possibleproduct for calves at the most criticaltimes such as at weaning time or useof a less expensive and active productin adult stock for primarily preven-tive or prophylactic purposes. Pro-ducers who do treat cattle for inter-nal and external parasites havetraditionally done so in spring andfall. This practice is associated withthose times when the herd wasworked for processing new calves inspring and weaning, pregnancychecking, and other procedures inthe fall. There is a great deal of meritin de-worming on these occasions,and deviations from the pattern arerare except in cases where emergencytreatments may be warranted. Eventhough these treatment times areconvenient and apparently mostpractical, they are not necessarily themost efficient and cost effective timesto prevent and control parasitism.

A key word in parasite control isprevention, preventing the danger-ous buildup of larval contaminationon pastures that can lead to subclini-cal parasitism (the unseen variety inwhich productivity is lost) andclinical parasitism, which can causegreat productivity losses and deaths.It has long been considered thatmost effective and rational preven-tion and control of parasitism mustbe based on epidemiology of the

parasites or the seasonal populationdynamics of the worms in cattle andon pasture in relation to weatherfactors and management conditions.Such information must be known forspecific regions; it is known andavailable for Louisiana and othersouth-central and southeasternportions of the United States. Onthis basis the most appropriate orstrategic times for de-wormingtreatment of cattle in different ageclasses can be selected. Knowledge ofthe epidemiology of nematodeparasites is also important in beingable to judge what pastures are ofhigh or low levels of pasture con-tamination in different seasons.

Strategic de-worming means thatcattle are treated at specific times inwhich maximal effects can be de-rived. Some particular dates fortreatment may appear to the pro-ducer to be inconvenient, impracti-cal, or impossible. However, mostepidemiologically correct treatmenttimes should coincide with periods inwhich de-worming is provided withother management procedures.

Cattle of all ages are exposed tothe same nematode infectivitypotential during the course of a year.The actual numbers of larvae in-volved in such seasonal changes,however, will vary from high, underpoor management conditions, to lowunder conditions of good manage-ment and parasite control. Basically,under poor or good parasite controlmeasures, highest rate of infectionbegins during late fall and increasesto peak levels in spring. Keep inmind, however, that with goodparasite control, numbers of larvaeand effects of parasitism are reduced.As indicated earlier, young cattle upto a few months post-weaning aresusceptible to Type I Ostertagiadisease, and yearlings, replacementheifers, and older stock are affectedby Type II disease. Infection withthe medium stomach worm does not

always result in outright disease, butwith heavy infections, disease prob-lems may be severe.

Regardless of the susceptibility ofthe young or resistance of oldercattle to infection, all age classes ofcattle are subject to the same yearlypatterns of infection risk. In essence,considering late summer/early fall asa starting point, when infection riskis lowest, the prime or first step is toadminister de-worming treatmentfor preventing the expected increaseof infection risk from late winterthrough spring. Waiting for thetraditional spring treatment time,mid-March to mid- May, can be alittle late in achieving most efficientprevention of the spring pastureinfectivity peak. Consequently, asecond treatment at 8 to 12 weeksafter the fall treatment, in January orFebruary, would be recommended.

Improved CattleResistance to ParasitesThrough Management

and De-wormers

Up to a year of age cattle de-velop little resistance to worminfections, but after this they candevelop resistance to several wormsand their effects. The best possiblelevel of nutrition is a key factor inproviding for development of resis-tance. Fertilization, weed control,use of best adapted forages, andmaintenance of stocking rates tokeep forages maximally harvested,provide excellent nutrition. Use ofde-wormers at strategic times whichreduce pasture contamination cansubstantially reduce infection ratesand enhance cattle resistance toinfection.


Drug Resistance in CattleNematodes

Drug resistance in nematodeparasites of sheep and goats, includ-ing resistance even to newendectocidal compounds, has be-come a major worldwide problem,most notably in Australia and NewZealand, but also in South America,Europe, Africa, and the UnitedStates. Increasing evidence for itsexistence for some nematode para-sites of horses has been reported,and drug resistance for some wormsof swine has been observed inEurope. There is little evidence tosupport drug resistance in cattlenematodes, but experts in thisfield warn of the potential for it tooccur. In the last decade or two,there has been only the occasionalreport about one species of worm oranother being resistant to effects of aparticular drug. In recent years,there have been several reports ofcattle nematodes being resistant tobenzimidazole drugs as well as toendectocides in New Zealand. This isa very localized situation and mayrelate to management and treatmentfrequency.

Cattle, for the most part, are notmanaged as closely and intensively assheep. Most notably, cattle havenever been treated for parasites atthe frequency sheep are treated. It isgenerally agreed that cattle nema-todes have a genetic makeup similarto those of sheep for drug resistanceselection. However, there are anumber of complex factors involvedbesides treatment frequency, such asgeneral differences in managementof cattle and sheep, differences ingrazing behavior, and differencesbetween rapidly disintegrating sheepfecal pellets and the larger, morecompact, mass of cattle feces.

A large percentage of cattle onfarms or ranges, especially very smallherds, may never be treated for

parasites. In some instances treat-ment may be given once a year. Insuch cases, conditions for resistanceselection would be essentially nil.However, in some cases, wheremultiple treatments may be given inthe same year to cattle in a closedherd, conditions for drug resistancecould be increased. Recommenda-tions for strategic treatments call fortwo or three treatments per year,particularly for cattle from weaningthrough 16 to 18 months of age.This level of treatment, if deemedaffordable, feasible, and profitable,should not enhance development ofdrug resistance. Availability of thenewer endectocidal products withpersistent anthelmintic activity couldallow for only one or two treatmentsper year in young cattle. In the caseof the ivermectin SRB only onetreatment should be given to youngcattle. Drug resistance in cattlenematodes is not a problem, per-

ceived or real, but the potentialexists with overuse and indiscrimi-nate use of de-wormer compounds.There is a general tendency todaythat increased numbers of cattle arebeing treated more frequently thanbefore because of ease and conve-nience of modern drug formulations,for example injectables and pour-onproducts. If two or three treatmentsare given to the same cattle in a year,it would be appropriate for one ofthe treatments to be with a drug of adifferent chemical class from that ofthe other two treatments, for ex-ample fenbendazole for one and anendectocide for the other two.

Costs to industry to develop newdrugs, chemicals, or other parasitecontrol agents and bring them tomarketing are astronomical. It istherefore imperative that the highefficacy of today’s excellent de-wormers be protected as much aspossible through judicious use.

Yearling cattle on 5-acre pastures in worm control experiment at the Red River ResearchStation, Bossier City, Louisiana.



TreatmentRecommendations

The question of treatmentrecommendations for preventionand control of gastrointestinalnematodes of cattle is one thatrequires consideration of manyfactors. Under the climatic condi-tions of Louisiana and other statesalong the Gulf of Mexico, which arehighly favorable to parasite propaga-tion through most of the year, it isnot a question of whether to treat,but when are the best and mosteconomically beneficial times fortreating cattle. Some of the factorsthat must be considered are type andlevel of management of forage andcattle, history of problems withparasite infections, the large varietyof available anthelmintics ordewormer products that vary informulation or means by which theyare administered (drenches,injectables, pour-ons, boluses, in-feed medication), spectrum ofefficacy against internal and externalparasites, cost, and overall herdhealth objectives of the producer.

There are probably a few pro-ducers who never treat their cattlefor internal parasites, while a fewothers may treat on a salvage basisonly when parasite problems areobvious or suspected. A majority ofproducers probably treat for internalparasite control at least once a year.Many may follow the traditionalpractice of herd treatment duringspring and fall. Information abouttreatment for internal parasites maybe obtained by producers fromseveral sources, including veterinar-ians, university extension personnel,drug company representatives,agricultural consultants, friends,television, magazines, and othermedia. More often than not, specificor general times of treatment are notincluded with recommendations fora given product.

Research on nematode parasitesof cattle over many years in theLouisiana Agricultural ExperimentStation at northern, central, andsouthern locations in the state hasindicated that weather conditions ofOctober through May provideoptimal circumstances for develop-ment and survival of nematode free-living stages or high infection risk onpasture. Therefore, it is this periodthat must be the focus of preventionand control programs. The period isvery long and coincides with bestforage production on pasture, that iswinter annuals and spring growth ofperennial forages such as bahiagrassand bermudagrasses. Under theseconditions, a single treatment ofcattle in the fall is generally notsufficient to protect them fromincreasing reinfection for the entirewinter-spring grazing season. Theexception to this would be treatmentin fall with the ivermectin SRB.

Among the different cattle ageclasses, stocker calves and replace-ment heifers require the most atten-tion regarding parasite controlprograms. From the time of wean-ing, these cattle are expected tomake maximal gains. Recommenda-tions were, and remain, that suchcattle require two or possibly threetreatments with benzimidazoledrugs, fenbendazole, albendazole, oroxfendazole, to adequately protectthem from the time of weaning inthe fall through spring of the follow-ing year. Such treatments are war-ranted at weaning in September-November and again in the spring(April-June). A third and possiblyoptimal treatment time is late winter(February-March). With the short-term killing action of the benzimida-zole drugs, length of the winter-spring grazing season and generalfavorability of weather conditions forparasite propagation, the multipletreatments are necessary to achievean adequate level of parasite control

in stockers and replacement heifersand to reduce pasture contamina-tion. Three treatments with benzimi-dazole drugs at 4- to 5- week inter-vals from the time of weaning mightbe substituted for, and achieve thesame level of control as, the treat-ment levels spaced at two to threemonths apart. With the newerendectocide products and theirpersistence of anthelmintic activity,frequency of treatments is reduced.As indicated earlier, the worm-killingactivity of the endectocides extendsfor 3 to 6 weeks, rather than the 2 to3 days for benzimidazoles.Endectocides for winter-springcontrol could thus be given tostockers and replacement heifers atweaning and 10 to 12 weeks later foreffective protection and controlthrough spring (Figure 11).

The following treatment recom-mendations should be appropriatefor most cattle enterprises in Louisi-ana and south-central and southeast-ern sections of the United States.

Mature CowsJuly-August: Most effective

time for removal of parasites andreducing rate of infection. Duringthe heat of summer, treatment canremove adults and larval stages ofnematodes including Ostertagia-inhibited larvae. Thus, parasites inthe cattle are removed at a timewhen hot and dry or alternating wetand dry conditions act to kill parasiteeggs and larvae on pasture. Potentialreinfection is greatly reduced afterthe summer treatment and can havelasting effect well into fall, if thecattle are not placed on a contami-nated pasture. If mature cows are tobe treated only once a year, this isthe best time to do it.

In areas of liver fluke prevalence(bottomlands of Mississippi and Redrivers and coastal marsh areas),treatment may be moved forward tolate August to allow flukes acquired



September 15-November 15:Traditional fall treatment. Thistreatment time is usually moreconvenient than the two indicatedearlier because it usually coincideswith weaning for spring born-calves.Nematodes, flukes, and ectoparasitescan all be controlled by treatment atthis time. However, Ostertagia-inhibited larvae (from accumulationin cattle during spring-summer)would have largely matured to egg-laying adult worms in August-September, and fluke infections mayhave been transmitted with mild andwet fall weather. Thus, before thistreatment, there would be someinterval of time in which theseparasites could have some ill effecton the cows and also produce morepasture contamination and increasedinfection risk for new calves.

February 15-April 1:Traditional spring treatment. Thistreatment is usually given prior tothe breeding season. Again, this is amore convenient time for manyproducers who may have to schedulework around row-crop farming orother non-livestock enterprises, butit is not the best time for parasitecontrol. Treating at this time willremove parasites from the cattle, butthe parasites have had all fall andwinter to adversely affect the cowsand contaminate pastures with eggs/larvae. If this is the only annualtreatment to be given, very highparasite populations can have accu-mulated in animals and on pasture,the latter posing a significant infec-tion potential for new spring calvesor fall-born calves. Treatment at thistime, in combination with a latesummer or fall treatment, can be avery effective parasite control pro-gram. However, if the only annualtreatment is given early in the year, itis not the time to get the mostbenefit from dollars spent on parasitecontrol.

Figure 11. Seasonal pattern of infection risk with gastrointestinal nematodes and lungwormof cattle. (A) The natural seasonal infection risk pattern with nematode parasites inLouisiana. Peak levels occur from late winter into spring, decrease in the warmer months,and begin to increase again in the fall. (B) Effect of anthelmintic/de-wormer treatment ascommonly used in the spring and fall. Parasite infection is not eliminated totally, but it isgreatly reduced, and profit should be realized rather than economic loss.

in the previous spring to reach amaturity level that will ensure effec-tive treatment. Treatment with any ofthe pour-on endectocides at this timewould control cattle grubs and liceand provide some short-term reduc-tion in horn fly populations. Spring-born calves, of which the producerplans to retain ownership, can betreated for nematode parasites at thistime also and given routine calfhoodvaccinations. The calves would betreated for parasites again at weaningand given booster vaccinations.Calves, generally, would not requiretreatment for flukes at this time.

January-February15: Elimina-tion of parasites when cattle aremost likely to be stressed. Treat-ment at this time removes parasitesand should help in reducing suscepti-bility to infection when animals arealready under nutritional, environ-mental, and gestational stress. Thistreatment would also reduce pasturecontamination levels, which other-wise would be available to infect fall-born calves with mother cows orspring calves that would soon beborn. Fluke and external parasitecontrol could also be affected as indi-cated for the July-August treatment.


B

A


CalvesAll calves that will be retained by

the producer should be treated forparasites and given regular calfhoodvaccinations at 2 to 4 weeks prior toweaning. They should be re-treatedfor parasites and given booster shotsof appropriate vaccines at weaning.

Whether calves are sold atweaning or retained for herd replace-ment, most producers probably donot treat nursing calves (3 to 6months old) for parasites prior toweaning. Spring-born calves wouldgenerally not begin to acquirenematode parasites in any substantialnumbers until they are 2 to 3months old. Older calves likely pickup more infection than calves bornlater in the calving season. Infectionsin the spring-born calf can build upto sizeable numbers by June or Julyand would usually be highest neartime of weaning. With calves to besold or retained after weaning,treatment for nematodes in June orJuly can result in substantially betterand cost-effective weaning weightsthan without treatment.

Replacement HeifersSpring-born heifers treated at

weaning in October or Novemberwith an endectocide and flukicideand put on a relatively clean pastureor one of low infection risk shouldbe sufficiently protected fromnematode and fluke infections untilafter the first of the year. Treatmentagain with an endectocide andflukicide in late February or Marchshould ensure that the heifers enterthe breeding season with low levelsof parasitism. Treatment when bullsare removed from the breeding herdin July should effectively removemature and immature worms,including inhibited larvae of Osterta-gia, and also reduce ectoparasitepopulations. One treatment with thelong-acting ivermectin SRB could besubstituted for the last two sug-

gested treatments, in February-March and July. Following a treat-ment shortly before the calvingseason, the heifers should be ready togo on the regular herd treatmentschedule.

Whether spring-born or fall-born, both first- and second-calfheifers remain highly susceptible tonematode and fluke infections andtheir effects. This may be moreobvious in first- calf heifers, but inmany instances, it may be consideredthat the second-calf heifer is matureenough to have developed resistanceto infection. On the contrary, whilestill nursing her first calf and being ingestation with the second calf, thisyoung cow is highly susceptible tonematode infection and should beprotected from effects of parasitismjust as done for the first-calf replace-ment.

Fall-born heifers, which shouldbe treated for parasites at weaning inJune or July and put on clean pas-ture, may not require treatmentagain until just before the breedingseason in December or January.Treatment again at the end of thebreeding season in March or Aprilwould probably be cost effectivebecause this is during the peaktransmission period. Treatment withthe ivermectin SRB in Novembercould effectively be substituted forthe latter two treatments. A treat-ment with one of the endectocides inJuly would allow the heifers to enterthe calving season with relatively fewinternal and external parasites. Afterthese heifers have calved, the regularcow-herd treatment schedule shouldbe appropriate for them, subject tothe caution indicated above for thesecond-calf heifer.

Stocker CalvesAll newly acquired stocker calves

should be given all appropriatevaccinations and treated with anendectocide as soon as possible after

they are received to prevent intro-duction and spread of infectiousdisease and contamination of pas-tures with nematode parasites.Home-raised calves should receivethese treatments prior to weaning asmentioned earlier. Since the primaryobjective of a stocker program is toconvert forage to pounds of calfweight, as economically as possible, acomprehensive plan for parasitecontrol should be a major part of theprogram.

Spring-born, fall-weaned calvesthat will be grazed on winter-springannual pastures can be allowed tocarry low levels of parasitism prior togoing on the fresh forage. Theyshould be treated with an endecto-cide 2 or 3 days before going on thewinter pasture. Thus, the calves willhave potential to make excellentgains when the forage is available forthem to reach that potential. Asecond endectocide treatment at 60to 80 days into a 120- to 150-daygrazing season would in most casesbe economically feasible. Treatmentwith the ivermectin SRB when thecalves go on winter pasture could besubstituted for the two treatmentsjust indicated. If grazing is to becontinued on summer forages afterthe winter pasture is depleted,another treatment with anendectocide would be beneficialwhen the transition is made, in Mayor June.

Fall- or spring-born calves thatare overwintered on hay and stubbleand then grazed on warm-seasonperennial pasture in spring can beallowed to carry low levels of parasit-ism during winter. A great deal ofrisk, however, is involved in this.Nutritional deficiency and adverseweather conditions could exaggerateeffects of existing nematode infec-tion, help to propagate new infectionrisk, and possibly result in clinicalparasitism. If this type of manage-ment is the only option, treatment at



the beginning of the winteringperiod with a lower cost, short-duration anthelmintic could beeconomically beneficial, especially ifthe cattle can be provided withpasture not heavily contaminatedwith parasite eggs/larvae. Use of alonger acting endectocide wouldobviously offer more benefit. De-pending on the supply and quality ofhay and winter weather, such cattlemay require another treatment inlate winter. When summer perennialpasture is ready for grazing in spring,the cattle should be treated with anendectocide.

Regular or fixed treatmentprograms or schedules should bedeveloped and followed for adultcows. Schedules for young grazingcattle are more difficult to develop.Weather conditions, forage availabil-ity, levels of infection risk, and otherfactors vary from year to year.Therefore, control programs forstocker and replacement heifer calves

have to be more flexible. The objec-tive is to have the cattle ready tomake the most use of forage that isavailable. When available forage canprovide enough nutrients to producerapid calf gains, the calves need to beas free of parasites as possible to takefull advantage of the forage.

Dairy CattleThese recommendations have

been written primarily with the beefproducer in mind. All general prin-ciples in this publication, however,have direct application to dairycattle. All of the internal parasites indairy cattle are the same as those inbeef cattle, and the life cycles andseasonal dynamics of the parasites inrelation to climate are the same.Some of the differences in manage-ment of beef and dairy cattle have tobe considered, but essentially thetreatment recommendations alreadydiscussed would be applicable,especially for calves and replacement

heifers. Treatment restrictions fordairy cattle of breeding age, regardingwithdrawal time for milking, areindicated on product labels. Safe-guard, Eprinex, Cydectin, andRumatel are approved for use inlactating dairy cattle.

Anthelmintics and endectocidesindicated for use in parasite controlhave efficacy against the full spectrumof nematode parasites including thecattle lungworm and Ostertagia-inhibited larvae. In the United States,we are limited to only two products(albendazole and clorsulon) withefficacy against the liver fluke; theactivity of these products is largelylimited to adult flukes. Although thetapeworm (Moniezia) of cattle is notknown to cause any significant adverseeffects, some producers may wish totreat for this parasite. The newerendectocides have no activity againstthe tapeworm, but the benzimidazoleanthelmintics do have some level ofactivity in removing tapeworms.

This is not Wisconsin or Nebraska, but yearling cattle in a worm control experiment feeding on a rolled out round bale of Bermudagrass hayat the Red River Research Station, Bossier City, Louisiana.



James C. WilliamsDepartment of Veterinary ScienceLSU AgCenterTel (225) 578-6279Fax (225) 578-0400e-mail: [email protected]

Alvin F. LoyacanoDean Lee Research StationLSU AgCenterTel (318) 473-6523Fax (318) 473-6535e-mail: [email protected]

Non-profit Org.U.S. Postage

PAIDPermit No. 733

Baton Rouge, LA

Louisiana State University Agricultural CenterWilliam B. Richardson, ChancellorL. J. Guedry, Executive Vice ChancellorLouisiana Agricultural Experiment StationWilliam H. Brown, Vice Chancellor and DirectorLouisiana Cooperative Extension ServiceJack L. Bagent, Vice Chancellor and Director

The LSU AgCenter provides equal opportunitiesin programs and employment.

Produced by LSU AgCenter CommunicationsVisit our Web site: www.lsuagcenter.com

The intense interest and enthusiastic participation and cooperation of John W.Knox, Professor Emeritus, Red River Research Station, LSU AgCenter, is mostgratefully acknowledged. Much of the information in this publication was obtainedin numerous epidemiological and parasite control experiments conducted in coop-eration with our friend and colleague continuously between 1969 to 1987. Sincereappreciation is also extended to Dr. Doyle Chambers, Vice-Chancellor and DirectorEmeritus, LSU AgCenter, for his long-term interest and support of research oninternal parasitism of cattle.

Louisiana Agricultural Experiment StationLouisiana State University Agricultural CenterP.O. Box 25100Baton Rouge, LA 70894-5100

Research Information Sheet #104 August 2001 · Internal Parasites of Cattle in Louisiana and Other...

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