ParasiteResistance

2013 PASA Conference 2/7/2013

Susan Schoenian and Jeff Semler 1

STRATEGIES, TECHNIQUES AND

EXPERIENCE TO FOSTER PARASITE

RESISTANCE & RESILIENCE

SUSAN SCHOENIAN & JEFF SEMLER

UNIVERSITY 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).


• Sheep and especially goatsare 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, Trichostrongylusspp. 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 worm

Image from Novartis

Coccidia “nodules” in small intestines

Image from ScienceDirect



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Haemonchus Trichostrongylus Other

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6/7 7/1 7/29 8/25

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Haemonchus Trichostrongylus

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 ANIMAL

HAEMONCHOSIS

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. FEC

2358 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 epgfor 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 used

a) 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

ParasiteResistance

Education

goats roundworms

effects of internal

sciencedirectsusan schoenian

jeff semler4

jeff semler2

alot of sheep

pasa conference272013sheep

meningeal worm