Internal parasite control in sheep

SUSAN SCHOENIAN (Shāy-nē-ŭn)Sheep & Goat SpecialistWestern Maryland Research & Education Centersschoen@umd.edu - www.sheepandgoat.com

Internal parasites: the realities Internal parasites are the

primary health problem affecting sheep in warm, moist climates.

Except for goats, sheep are the most susceptible farm livestock to internal parasites.

Though it varies by geographic location and individual farm, worms are rapidly developing resistance to the anthelmintics.

Nowadays, successful worm control requires an integrated approach that does not rely solely on anthelmintics.

Anthelmintic = dewormer

What is a parasite?

A (generally undesirable) living

organism that exists by stealing the

resources produced or collected by another living

organism

Source: Wiktionary

There are two kinds of parasites.

1. Internal (endo) - a parasite that lives inside another organism.

2. External (ecto) - a parasite that lives on the blood of the host or lays eggs on their hide or in their nose.

There are two general kinds of internal parasites.

1) Helminths (multi-cellular)

a) Nematodes (roundworms)

b) Cestodes (tapeworms)

c) Trematodes (flukes)

2) Protozoa (single cell)

d) Coccidiae) Giardiaf) Cryptospordiu

m

Parasites “tend” to be species-specific.

HELMINTHSNematodes (roundworms)

Over 20,000 speciesLongRoundNot segmentedMicroscopicSexual reproduction

Male and female worms

Haemonchus contortus Barber pole worm

Scour wormsTrichostrongylus spp. Hair wormTeladorsagia Brown stomach wormOesophagostomum Nodule wormNematodirus spp. Threadworm

OtherLungwormsMeningeal worm

NEMATODE

Blood suckerFound in abomasumMost pathogenicCauses anemia, bottle jaw, and death.

Prolific egg producerDirect life cycleRequires warmth (60°F) and moisture to complete its life cycleShort 3 week life cycle

Barber pole wormHaemonchus contortus

NEMATODES

Found in abomasum and Intestines.Usually found in mixed infections with barber pole worm.Not as pathogenic as barber pole worm.Cause digestive problems (scouring) and ill thrift.

Similar life cycle and pre- patent period as barber pole worm.Egg laying capacity varies.Eggs look the same as barber pole worm.

“Scour” worms

Image source: NADIS UK

HELMINTHS Tapeworms (cestodes)

Over 1,000 speciesRibbon-likeFlatSegmentedHermaphroditesIntermediate hostVisible in feces

UsuallyNon- pathogenic Non disease-causingNo benefit to treatment

HELMINTHS Flukes (trematodes)

FlatOval-shapeLeaf-likeHermaphroditicRequire intermediate host: snail, slug

Damage liverCause anemia

PROTOZOA Coccidia

Single-cellSpore-formingMicroscopicCan reproduce sexually

or asexuallySpecies-specific

Eimeria spp.

Cause scouringDamage lining of small intestines.

Treat with amprolium (Corid) or sulfa drugs.Prevent with coccidiostats.

Integrated parasite management

Parasites Life cycle Host resistance Management Clean or safe pastures Multi-species grazing Pasture rest and rotation Alternative forages Nutritional management Zero grazing Genetic selection Manage refugia Targeted selective

treatmentYour approach to internal parasite control should be

integrated or holistic.

Parasite identificationWhat kind(s) of parasites are affecting your sheep?

FECAL EGG FLOTATION

To differentiate between strongyle (stomach) and tapeworm eggs and coccidia oocytes.

Can’t differentiate between strongyle (stomach) worm eggs except Nematodirus)

1. Do-it-yourself2. Public lab 3. Diagnostic lab4. Private lab5. Veterinarian

LARVAL ID

To differentiate between strongyle (stomach) worms (H. contortus, Teladorsagia, and trichostrongyles)

▪ University of Georgia▪ Other universities

LECTIN-STAINING TEST

Determine percent of Haemonchus contortus eggs in a fecal sample Oregon State University University of Georgia

Life cycle

• Eggs hatch and develop into infective larvae (L3).• Sheep ingest infective 3rd stage larvae (L3).• Immature adults (L4) and adult worms suck blood.• Adult worms lay eggs.

Host resistanceSheep and lambs vary in their susceptiiblity to parasitism.

MORE SUSCEPTIBLE

Weaned lambs Bummer lambs Late-born lambs Yearlings High-producing

females Periparturient ewe Thin animals Geriatric sheep Unadapted breeds Stressed animals

MORE RESISTANT

Mature sheep Dry ewes Pet sheep Mature wethers Sheep in good body

condition Fat sheep

Management

Good sanitation Use feeders Clean water Avoid

overgrazing Do not graze

below 2 inches. Time lambing to

minimize parasite infections.

Pasture rest and rotation Pasture rotation is a

recommended strategy for controlling internal parasites because it allows the use of cleaner (rested) pastures.

Intensive rotational grazing may not help to reduce parasitism unless rest periods are long enough.

Due to increased stocking rates, management intensive grazing may increase internal parasite problems in sheep and lambs.

It takes about 2 months of rest for a contaminated pasture to become relatively “clean” for sheep grazing.

Use of clean or safe pastures

A pasture that has not been grazed by sheep (or goats) for the past 6 to 12 months.

A pasture that has been grazed by adult cattle and/or horses for the past 6 to 12 months.

New pasture

A pasture that has been renovated with tillage.

A pasture in which a hay or silage crop has been removed.

A pasture that has been rotated with row crops.

A pasture that has been burned.

Alternative forages

Livestock that browse have fewer parasite problems.

Livestock grazing tall-growing forages will have less parasite problems.

80% of parasite larvae is found in the first two inches of vegetative growth.

Grazing tanniferous forages may reduce the effects of parasitism.

Sericea lespedeza Chicory Birdsfoot trefoil

Multi-species grazing

Sheep and goats share the same parasites, but they are different from the parasites that affect adult cattle and horses.

Producers who graze multiple species of livestock report fewer parasite problems with small ruminants.

Cattle and horses “vacuum” sheep/goat pastures of infective worm larvae.

Sheep, goats, and cattle have complementary grazing habits.

Nutritional management

Animals on a high plane of nutrition and in better body condition are better able to withstand worm burdens.

Nutrition in early pregnancy (fat stores) can affect the immune response to internal parasites.

Sheep receiving higher levels of protein prior to lambing have lower fecal egg counts.

Supplementing grazing lambs with protein has been shown to reduce fecal egg counts.

Nutritional supplementation is most likely to be beneficial when pregnant females and young animals are below optimal body condition at a time when pasture quality and/or quantity is limited.

Zero grazing

Sheep raised in confinement or dry lot (zero grazing) tend to have fewer worm problems.

Sheep put in confinement or dry lot do not usually get re-infected with worms.

Coccidiosis could still be a problem, if preventative measures are not taken.

Good sanitation Proper feeders Coccidiostats

Genetic selection

Breeds vary in their resistance to gastro-intestinal parasites. Resistant breeds: Gulf Coast

Native, Katahdin, St. Croix, Barbado.

There is as much difference within breeds as between breeds.

The 80-20 ruleApproximately 20 percent of the flock sheds 80 percent of the eggs onto pasture.

Parasite traits are moderately heritable.

Selection for parasite resistance will not adversely affect the growth of lambs or fertility of ewes.

Resistance Ability of host to

resist infection Measured by fecal

egg counts

Resilience Ability of host to

withstand challenge and/or infection.

For barber pole worm: measured by packed cell volume.

Slow down drug resistanceRufugia are worms that have not been exposed to anthelmintic treatment.

Do not deworm on a regular schedule.

Do not deworm all animals in a group.

Do not return treated animals to a clean pasture.

Give all anthelmintics orally at the proper dose.

Do not underdose.

Deworm new animals with anthelmintics from two different chemical classes.

Without refugia, worms will eventually be resistant to all

anthelmintics.

Targeted selective treatmentFive Point check©

Point What to check Which parasites

1 Eye

Paling of ocular membranesFAMACHA© eye anemia score

Barber pole wormLiver fluke

2 Back Body condition score All

3 RearDag scorefecal soilingevidence of scouring

Brown stomach wormHair wormThreadneck wormNodule worm

4 JawSub-mandibular edema (bottle jaw)

Barber pole wormLiver fluke

5 Nose Nasal discharge Nasal bots

FAMACHA© eye anemia score

Eye lid color

Packed cell volume

Treatment recommendation

1 Red > 28 Optimal No

2 Red-Pink 23-27 Acceptable No

3 Pink 18-22 Borderline ?

4 Pink-White 13-17 Dangerous Yes

5 White < 12 Fatal Yes

Body condition score (BCS)

Spine Transverse processes Muscle Fat

1 Individually clearly felt, sharp, obvious

Fingers easily pass underneath Very little No

2 Form a smooth line with deep undulations

Smooth round edges

Concave Very thin

3Only slightly detectable undulations

Well coveredhave to push firmly

to get fingers underneath

Not concaveNot convex

Moderate

4 Only detectable with firm pressure Cannot be

felt at all

Maximally developed

Convex

Thick

5 Not detectable Very thick

Dag Scores

Dag score Description Treatment recommendation

0 No fecal soilingNo indication for

treatment

1 Very slight soiling on edge of tail

No treatment

2 Slight soiling on edge of tail and on each side

Usually no treatment

3 Moderate soiling of tail and woolDag formation

Consider treatment

4Severe soiling extending far into

woolSevere dag formation

Treatment, crutching recommended

5Very severe

watery diarrhea extending to hocks

Treatment and crutching essential

Bottle jawSub-mandibular edema

Nasal discharge

Fecal egg countseggs per gram of feces

Indicate “potential” parasite burden in animal.

Indicate potential parasite contamination.

Use to determine level of drug efficacy.

Use to determine genetic differences in parasite resistance.

Limitations of fecal egg counts

Fecal egg counts are not always well-correlated with disease.

Presence of eggs or does not mean that the animal is clinically parasitized and needs treatment.

Absence of eggs or oocytes (coccidia) does not mean that the animal is parasite-free and not needing treatment.

Fecal egg count interpretatoin

Three classes of anthelmintics

1)Benzimidizoles2)Nicotinic agonists3)Macrocylic lactones

Benzimidazoles (BZD)

CHARACTERISTICS

White dewormers Water soluble Broad spectrum Wide margin of safety Efficacy against

tapeworms Efficacy against liver

flukes (albendazole) Widespread resistance Resistance is caused by

dominant gene

PRODUCTS

1) Fenbendazole [Rx]SafeGuard®, Panacur®

2) AlbendazoleValbazen®

3) Oxyfendazole [Rx]Synanthic®

Nicotinic agonists

CHARACTERISTICS

Levamisole Clear drench Water soluble Broad spectrum of activity Not effective against arrested

larvae Narrower margin of safety Resistance reported Resistance is caused by a

recessive gene

Morantel and Pyrantel Not effective against larval

stages

PRODUCTS

1)   Imidazothiaoles (IMID)

a) LevamisoleProhibit®, Levasol®

2)  Tetrahydropyrimidines (TETR)

a) Morantel [Rx]Rumatel®

b) Pyrantel [Rx]Strongid®

Macrocylic lactones (ML)

PRODUCTS

1) Avermectinsa) Ivermectin

Ivomec®b) Doramectin [Rx]

Dectomax®

2) Milbemycins a) Moxidecin

Cydectin® Quest® [Rx]

CHARACTERISTICS

Broad spectrum Wide margin of safety Effective against

external parasites Persistent activity Widespread

resistance, reported especially ivermectin

Resistance is caused by dominant gene

Improving (maintaining) the efficacy of treatment

Weigh animals to determine proper dose.

Do not underdose. Use proper drench

technique. Fast animals prior to

treatment. Give multiple

anthelmintics [Rx] Synergetic effect

Manage for refugia

How do you know if you have anthelmintic resistance on your farm?

1) DRENCHRITE® LARVAL DEVELOPMENT ASSAY

An in vitro test for the detection of resistance to all anthelmintic groups.

Need pooled fecal sample from 10 or more animals (minimum of 6)at least > 350 epg >500 epg preferred

▪ Animals with FAMACHA© scores of 3, 4, or 5 are more likely to have higher egg counts if barber pole worm is the primary parasite.

2) FECAL EGG COUNT REDUCTION TEST (FECRT)

Comparison of before and after fecal egg counts Benzimidizoles

7 days post-treatment Levamisole

7 days post-treatment Avermectins

14 days post-treatment

Should include “control” (untreated) animals in testing.

The future of parasite control“NATURAL” ANTHELMINTICS

Copper oxide wire particles

Copper sulfate Garlic Pumpkin seed Diatomaceous earth Pine bark Sericea lespedeza (leaf

meal) Others

FUTURE

Vaccine development They are testing a promising

vaccine in Australia The European community has

received a historically large grant to help develop vaccines for gastro-intestinal parasites in livestock.

New anthelmintics Zolvix®

Monepantel Startect®

derquantel + abamectin

Thank you for your attention.

Any questions?

Susan Schoeniansschoen@umd.eduwww.sheepandgoat.com

SMALL RUMINANT PROGRAM