1. 2013 PASA Conference 2/7/2013
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.
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2. 2013 PASA Conference 2/7/2013
GASTRO-INTESTINAL PARASITES
• 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).
GASTRO-INTESTINAL PARASITES
• 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!).
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3. 2013 PASA Conference 2/7/2013
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 I have
worms!
(gut, lung, meningeal)
2) Trematodes (tapeworms)
3) Cestodes (flukes)
Me, too!
2. Protozoa (single cell)
1) Coccidia
PRIMARY PARASITES AFFECTING
SHEEP AND GOATS
• Roundworms, especially
Haemonchus contortus • Coccidia (Eimeria spp.)
(barber pole worm).
• Other parasites (e.g.
meningeal worm) can be
• Also, Trichostrongylus a problem on individual
spp. and Teladorsagia farms or in some years.
(Ostertagia).
Barber pole worm Coccidia “nodules” in small intestines
Image from Novartis Image from ScienceDirect
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4. 2013 PASA Conference 2/7/2013
MOST ECONOMICALLY-DEVASTATING PARASITE
IS USUALLY HAEMONCHUS CONTORTUS.
2012 2010
100 100
80 80
60 60
40 40
20 20
0 0
6/2 6/28 7/26 8/22 6/7 7/1 7/29 8/25
Haemonchus Trichostrongylus Other Haemonchus Trichostrongylus Other
2011 2009
100
100
80
80
60 60
40 40
20 20
0 0
6/3 7/7 8/4 9/1 6/6 7/1 7/16 7/30 8/13 8/26 9/10 9/26
Haemonchus Trichostrongylus Other Haemonchus Trichostrongylus
LARVAE ID (PERCENT HAEMONCHUS IN RED) FROM WESTERN MARYLAND PASTURE-BASED MEAT GOAT PERFORMANCE TEST.
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.
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5. 2013 PASA Conference 2/7/2013
SYMPTOMS IN THE ANIMAL
HAEMONCHOSIS
1. Hyperacute (< 1 week)
• “Sudden death”
• No obvious signs
2. Acute (> 1 week)
• Anemia
• Edema (bottle jaw)
• Weight loss Voracious blood-sucker!
• Loss of body condition
• Anorexia
• Loss of stamina
• Diarrhea
3. Chronic (sub-clinical)
• Loss of performance
GENETICS OF PARASITES:
TWO TRAITS
RESISTANCE RESILIENCE
• Prevent parasitic disease • Tolerate (perform, remain
from establishing. healthy) despite parasite
burden (could still have
• Quantified by fecal egg
high egg count).
counts (FECs), which are
an estimate of the • For barber pole worm,
number of worms in the quantified by packed cell
animal’s gut. volume (PCV) and
estimated by FAMACHA©
EPG: eggs per gram (of feces) eye anemia scores.
PCV - percent; FAMACHA© - 1-5
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6. 2013 PASA Conference 2/7/2013
ABOUT FECAL EGG COUNTS (EPG)
• They are “relative”:
a “snapshot” in time. McMaster slide
• 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.
You can learn to do your own FECs.
ABOUT PACKED CELL VOLUME (PCV)
• Is proportion (%) of blood represented
by red blood cells.
McMaster slide
• Also known as blood hematocrit.
• 25 to 35 percent is normal in sheep/goats.
• Is usually lower for goats.
• Is estimated by FAMACHA© scores.
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
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7. 2013 PASA Conference 2/7/2013
OTHER IMPORTANT MEASUREMENTS
OF PARASITE RESILIENCE
• Body condition (1-5)
• Dag score (fecal soiling, 0-5)
• Coat condition
• Weight gain
Dagginess Weight loss Poor body condition
HERITABILITY (H2) OF
RESISTANCE AND RESILIENCE
RESISTANCE RESILIENCE
• Moderately heritable • Low heritability
~0.25 ~ 0.10
(higher for Katahdins)
• Less variability:
• Extremely variable: coefficient of variation
coefficient of variation usually between 20
is often over 100 and 40 percent.
percent.
Fecal egg counts are the standard for
improving parasite resistance in sheep.
Heritability (h2) is the proportion of phenotypic variation due to genetics.
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8. 2013 PASA Conference 2/7/2013
GENETIC RELATIONSHIP BETWEEN
RESISTANCE AND RESILIENCE
• Resistance and resilience are
usually positively correlated, Year Correlation
though measurement numbers 2007 0.29
may be negatively related. 2008 0.42
2009 0.18
e.g. FEC PCV and
2010 0.27
FEC FAMACHA© Score.
2011 0.14
• In the Western Maryland Genetic correlations range from -1 to +1
and are an indication of the amount of
Pasture-Based Meat Goat variation that two traits share.
Performance Test, FEC and
FAMACHA© scores have had In New Zealand, they found no
correlation between parasite
positive correlations, but they resistance and parasite resilience.
have not been very strong.
IN OUR BUCK TEST, WE USE FECAL
EGG COUNTS (FEC) TO EVALUATE
GENETIC RESISTANCE TO PARASITES.
NOT TO MAKE DEWORMING DECISIONS.
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9. 2013 PASA Conference 2/7/2013
WE USE FAMACHA© SCORES TO
ESTIMATE PACKED CELL VOLUME
…AND MAKE DEWORMING DECISIONS.
TWO WAYS TO SELECT FOR
PARASITE RESISTANCE AND RESILIENCE
BETWEEN BREED WITHIN BREED
• Some breeds are naturally • There is as much variation
more resistant and resilient to within a breed as between
internal parasites (round- breeds.
worms) than others.
• The 80-20 rule: it is estimated
• This is well-documented in that 20-30 percent of the flock
sheep; not very well- or herd is responsible for
documented in goats causing 70 to 80 percent of the
(mostly anecdotal). pasture contamination
• Resistant breeds tend to be (fecal egg outlay).
those with tropical origins or • Parasite resistance (FECs) is a
landrace breeds that have moderately heritable trait.
naturally adapted to their
environment (“survival of the
fittest”).
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10. 2013 PASA Conference 2/7/2013
(MORE) RESISTANT BREEDS
SHEEP GOATS
• Landrace hair sheep Not
• Kiko
1) St. Croix • Boer
2) Barbados Blackbelly • Spanish • Nubian
3) American Blackbelly • Swiss dairy
• Myotonic
• Composite hair x wool
1) Katahdin
• Medium wool
1) Gulf Coast Native
Florida Native St. Croix:
the most
• Dorper - not resistant, but resistant
maybe more resilient. breed in US.
• Others (?)
WITHIN BREED SELECTION
ANY BREED (OR POPULATION) CAN BE SELECTED
FOR IMPROVED PARASITE RESISTANCE.
2012 Western Maryland Pasture-Based Meat Goat Performance Test
Avg. FEC
2358 epg
80:20 rule: Fecal egg counts are not evenly dispersed in a herd or flock.
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11. 2013 PASA Conference 2/7/2013
Selection for parasite resistance in Australia
Selection for parasite resistance in Australia
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12. 2013 PASA Conference 2/7/2013
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.
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13. 2013 PASA Conference 2/7/2013
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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14. 2013 PASA Conference 2/7/2013
2012 Western Maryland Pasture-Based Meat Goat Performance Test
1
2
3
4
5
Top 10 6
7
8
9
10
10
9
8
7
6
Bottom 10 5
4
3
2
1
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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15. 2013 PASA Conference 2/7/2013
2012 Western Maryland Pasture-Based Meat Goat Performance Test
1
2
3
4
5
Top 10 6
7
8
9
10
10
9
8
7
6
Bottom 10 5
4
3
2
1
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 Let me
out!
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 Fecal egg counts are a measure
the herd or flock. of pasture contamination.
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16. 2013 PASA Conference 2/7/2013
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. Kiko x Boer
• 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 Test
Avg. FEC: 232 epg; Avg. FAM: 1.7; ADG ratio: 181%
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