FosteringParasiteResistance

STRATEGIES, TECHNIQUES AND EXPERIENCE TO FOSTER PARASITE RESISTANCE & RESILIENCE

SUSAN SCHOENIAN & JEFF SEMLERUNIVERSITY OF MARYLAND EXTENSION

GASTRO-INTESTINAL PARASITES

Gastro-intestinal parasites are the primary health problem affecting sheep and goats in warm, moist climates and areas with summer rainfall.

Sheep and especially goats are more susceptible to the effects of internal parasites than other farm livestock.

Goats are not natural grazers, nor well-adapted to moist climates.


• Sheep and goats share the same internal parasites (except for coccidia).

• Not all parasites are pathogenic or equally pathogenic.

• Close grazing facilitates the ingestion of infective worm larvae (L3).

• Grazing near fecal pellets also facilitates ingestion of infective worm larvae (L3).

L3


• Sheep and especially goats are slow to develop immunity to internal parasites and experience a relaxation of immunity around the time of parturition (known as the “periparturient egg rise”).

• Worms have developed varying degrees of resistance to ALL of the dewormers (anthelmintics).

• Drug resistance is inevitable! Worms will eventually develop resistance to any new dewormer, quicker if we over-use it or use it improperly (like we’ve done in the past!).

SHEEP AND GOATS CAN BE AFFECTED BY A VARIETY OF INTERNAL (AND EXTERNAL) PARASITES AND IT IS NORMAL FOR THEM TO HAVE SOME WORMS IN THEIR GUTS AND EGGS IN THEIR FECES.

1. Helminths (worms)

1) Roundworms(gut, lung, meningeal)

2) Trematodes (tapeworms)

3) Cestodes (flukes)

2. Protozoa (single cell)

1) Coccidia

I have worms!

Me, too!

PRIMARY PARASITES AFFECTING SHEEP AND GOATS

• Roundworms, especially Haemonchus contortus (barber pole worm).

• Also, Trichostrongylus spp. and Teladorsagia (Ostertagia).

• Coccidia (Eimeria spp.)

• Other parasites (e.g. meningeal worm) can be a problem on individual farms or in some years.

Barber pole wormImage from Novartis

Coccidia “nodules” in small intestinesImage from ScienceDirect

6/3 7/7 8/4 9/10

20

40

60

80

100

2011

Haemonchus Trichostrongylus

Other

6/7 7/1 7/29 8/250

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40

60

80

100

2010


Other

6/2 6/28 7/26 8/220

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40

60

80

100

2012


Other

6/6 7/1 7/16 7/30 8/13 8/26 9/10 9/260

20

40

60

80

100

2009


LARVAE ID (PERCENT HAEMONCHUS IN RED) FROM WESTERN MARYLAND PASTURE-BASED MEAT GOAT PERFORMANCE TEST.

MOST ECONOMICALLY-DEVASTATING PARASITE IS USUALLY HAEMONCHUS CONTORTUS.

THE BARBER POLE WORM IS AN INCREDIBLE PARASITE!

• Very pathogenic: kills a lot of sheep and goats, especially weanlings.

• Difficult to control• Simple, direct life cycle• Prolific egg layer• Undergoes hypobiosis

(inhibited developmental stage)

• Adaptable: from the Tropics to the Artic.

SYMPTOMS IN THE ANIMALHAEMONCHOSIS

1. Hyperacute (< 1 week)• “Sudden death”• No obvious signs

2. Acute (> 1 week)• Anemia • Edema (bottle jaw)• Weight loss• Loss of body condition• Anorexia• Loss of stamina• Diarrhea

3. Chronic (sub-clinical)• Loss of performance

Voracious blood-sucker!

GENETICS OF PARASITES: TWO TRAITS

RESISTANCE

• Prevent parasitic disease from establishing.

• Quantified by fecal egg counts (FECs), which are an estimate of the number of worms in the animal’s gut.

EPG: eggs per gram (of feces)

RESILIENCE

• Tolerate (perform, remain healthy) despite parasite burden (could still have high egg count).

• For barber pole worm, quantified by packed cell volume (PCV) and estimated by FAMACHA© eye anemia scores.

PCV - percent; FAMACHA© - 1-5

ABOUT FECAL EGG COUNTS (EPG)

• They are “relative”: a “snapshot” in time.

• A single egg count is not necessarily a good measure of the parasite burden in an individual animal; however, it is a measure of pasture contamination.

• Fecal egg counts include all strongyle-type eggs: Haemonchus, Trichostrongylus, and Teladorsagia: you must hatch eggs to identify strongyle species by worm larvae.

• Worms vary in their egg-laying ability.

McMaster slide

You can learn to do your own FECs.

ABOUT PACKED CELL VOLUME (PCV)• Is proportion (%) of blood represented

by red blood cells.

• Also known as blood hematocrit.

• 25 to 35 percent is normal in sheep/goats.

• Is usually lower for goats.

• Is estimated by FAMACHA© scores.

McMaster slide

Score Color PCV Tx?

1 Red > 28 No

2 Red-Pink 23-27 No

3 Pink 18-22 ?

4 Pink-White 13-17 Yes

5 White < 12 Yes

OTHER IMPORTANT MEASUREMENTS OF PARASITE RESILIENCE

• Body condition (1-5)

• Dag score (fecal soiling, 0-5)

• Coat condition

• Weight gain

Weight loss Poor body conditionDagginess

RESISTANCE

• Moderately heritable~0.25 (higher for Katahdins)

• Extremely variable: coefficient of variation is often over 100 percent.

RESILIENCE• Low heritability

~ 0.10

• Less variability: coefficient of variation usually between 20 and 40 percent.

Fecal egg counts are the standard for improving parasite resistance in sheep.

HERITABILITY (H2) OF RESISTANCE AND RESILIENCE

Heritability (h2) is the proportion of phenotypic variation due to genetics.

GENETIC RELATIONSHIP BETWEEN RESISTANCE AND RESILIENCE

• Resistance and resilience are usually positively correlated, though measurement numbers may be negatively related.

e.g. FEC PCV and FEC FAMACHA© Score.

• In the Western Maryland Pasture-Based Meat Goat Performance Test, FEC and FAMACHA© scores have had positive correlations, but they have not been very strong.

Year Correlation

2007 0.29

2008 0.42

2009 0.18

2010 0.27

2011 0.14

Genetic correlations range from -1 to +1 and are an indication of the amount of

variation that two traits share.

In New Zealand, they found no correlation between parasite

resistance and parasite resilience.

IN OUR BUCK TEST, WE USE FECAL EGG COUNTS (FEC) TO EVALUATE GENETIC RESISTANCE TO PARASITES.

NOT TO MAKE DEWORMING DECISIONS.

WE USE FAMACHA© SCORES TO ESTIMATE PACKED CELL VOLUME

…AND MAKE DEWORMING DECISIONS.

TWO WAYS TO SELECT FOR PARASITE RESISTANCE AND RESILIENCE

BETWEEN BREED

• Some breeds are naturally more

resistant and resilient to internal

parasites (round-worms) than

others.

• This is well-documented in

sheep; not very well-documented

in goats

(mostly anecdotal).

• Resistant breeds tend to be those

with tropical origins or landrace

breeds that have naturally

adapted to their environment

(“survival of the fittest”).

WITHIN BREED

• There is as much variation within a breed as between breeds.

• The 80-20 rule: it is estimated that 20-30 percent of the flock or herd is responsible for causing 70 to 80 percent of the pasture contamination (fecal egg outlay).

• Parasite resistance (FECs) is a moderately heritable trait.

(MORE) RESISTANT BREEDS

SHEEP

• Landrace hair sheep

1) St. Croix

2) Barbados Blackbelly

3) American Blackbelly

• Composite hair x wool

1) Katahdin

• Medium wool

1) Gulf Coast NativeFlorida Native

• Dorper - not resistant, but maybe more resilient.

• Others (?)

GOATS

• Kiko

• Spanish

• Myotonic

Not

• Boer• Nubian• Swiss dairy

St. Croix: the most resistant

breed in US.

WITHIN BREED SELECTIONANY BREED (OR POPULATION) CAN BE SELECTED FOR IMPROVED PARASITE RESISTANCE.

80:20 rule: Fecal egg counts are not evenly dispersed in a herd or flock.

Avg. FEC2358 epg

2012 Western Maryland Pasture-Based Meat Goat Performance Test

Selection for parasite resistance in Australia

HOW TO SELECT FOR PARASITE RESISTANCE

• The immune system needs to be stimulated by a worm challenge before genetic differences can be expressed.

• Measure fecal egg counts when animals are between 6 and 12 months of age.

• No sooner than 6 weeks after weaning.

• A high worm load is needed to do the best job of separating resistant vs. susceptible animals;

• Avg. FEC of 500-1000 epg for barber pole worm

• Less than 10% of animals should have zero egg counts.

PROTOCOL FOR MEASURING RESISTANCE IN KATAHDINS

Source: NSIP, David Notter, Virginia Tech, 2004

HOW TO SELECT FOR PARASITE RESISTANCE

• Take all samples on same day.

• Store samples in a cool place to prevent eggs from hatching.

• Compare animals in same contemporary group.

• Compare individual FECs to group average.

• Heritability will be higher if more than one FEC is used for comparison.

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All goats were triple-dewormed (moxidectin + levamisole + albendazole) on 6/2. Twelve days later, the average fecal egg count was near zero.

HOW TO SELECT FOR PARASITE RESILIENCE

• Many criteria can be useda) Packed cell volume

b) FAMACHA© score

c) Time from fixed point that deworming is required

d) Number of times dewormed during specific time period.

e) Body condition score

f) Dag scores (scour worms)

g) Growth rates

• Cull animals that require frequently deworming.

• Select animals that do not require deworming and whose parents don’t require deworming.

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All goats were triple-dewormed (moxidectin + levamisole + albendazole) on 6/2. For the next 8 weeks, the average FAMACHA© score improved and no goat required deworming.

WE WANT BOTH RESISTANCE AND RESILIENCE!

• You don’t want have to deworm your stock, but you also don’t want to have animals that deposit a lot of eggs onto the pasture.

• Heavily-contaminated pastures lead to clinical parasitism, as there are almost always susceptible animals in the herd or flock.

Fecal egg counts are a measure of pasture contamination.

Let me out!

IT IS MOST IMPORTANT THAT THE MALE BE RESISTANCE TO PARASITES

There are large differences between sires for resistance.

WHAT WILL HAPPEN IF YOU DON’T PAY ATTENTION TO PARASITES?

• Eventually all the dewormers will stop working on your farm.

• You will need to feed more so that your animals can tolerate parasitic burdens.

• You’ll want to raise your sheep and goats in complete confinement so that they are not exposed to much infective worm larvae.

• You’ll have to stop raising sheep and especially goats.

• Your compost pile will get full. Top-performing buck from 2011 TestAvg. FEC: 232 epg; Avg. FAM: 1.7; ADG ratio: 181%

Kiko x Boer

QUESTIONS?

THANK YOU FOR YOUR ATTENTION.

Kiko and crossbred bucks from 2012 test.

FosteringParasiteResistance

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