Internal Parasite Management in Pasture-Based Sheep

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Internal Parasite Management
in Pasture-Based Sheep
Kathy Bielek
kathy.bielek@gmail.com

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Acknowledgements
• Dr. William Shulaw (OSU Extension
Veterinarian)
• Rory Lewandowski (OSU Extension,
Wayne County)

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Cost of Parasites
• Reduced milk production in ewes
• Slower lamb growth
• Appetite suppression
• Reduced wool production and quality
• Reduced fertility
• Less immunity to other diseases
• Lamb deaths

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The “costs” of parasitism
• “…thus acquisition of immunity in the
young lamb has a higher priority than
growth, but in the adult, expression of
immunity will have lower priority than
reproductive effort…”
Sykes and Coop New Zealand Veterinary Journal
2001;49:222-226.

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How do we “manage” internal parasites
in sheep and goats?
Approaches
Conquer or
Eliminate
Co-exist Avoid

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Conquer by Chemicals
• Requires regular, by the
calendar, drenching with a
chemical dewormer.
• Requires an effective
chemical dewormer
• Requires development of
new chemical brought to
market about every 5
years

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Drug resistance: How Does It Develop?
• Drug resistance develops as a genetic trait.
•Once resistance is present, it is likely to be permanent.
• Resistance develops when worms have frequent exposure
to a drug.
• A major cause of drug resistance is under dosing.
• underestimating weight
• incorrect dose calculation
• incorrect dilution of products
• improperly calibrated equipment
• Treatment of ALL animals and movement to a “safe” or
“clean” pasture

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TREATMENT
RESISTANCE
SELECTION
IN ADULT
WORMS

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100% - and
survivors of TX
no refugia of
unselected
worms
On the new pasture

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5%
95%
Refugia: parasites not exposed to
chemicals and selection pressure

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Log of
conc.
ng/ml
0 10 20 30 40 50 60 70
from: Shoop et al. 1997. J Vet Pharmacol Therap. 20
(Suppl. 1), 12-14
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
moxidectin
ivermectin
200 ug/kg oral dose
35 days of selection for
resistance in larvae
acquired from pasture

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You may not think you have a problem
• Resistance is relative
– Not all worms on farm
are resistant
• Killing some worms
may relieve disease
symptoms
– Clinically it appears
that the treatment was
effective

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Drug Resistance
All control programs that rely strictly on the
use of chemical dewormers will eventually
fail as a result of development of
resistance.
The question is how soon it will happen on
YOUR farm, or how well can you develop
strategies that minimize drug use.

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Avoid Parasites if Possible
• Especially useful when pasture options or
acreage are limited
• Fall lambing
• Early wean, raise lambs in barn or feedlot
• France: lactating ewes to pasture during the day,
back to barn at night. Lambs remain in the barn.
(Also Wooster bulletin from April, 1900)
• Goats: Consider the use of browse and brush to
avoid contact with the parasite.

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Early weaning and dry lot

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Management Concepts for co-existing
• Nature bats last, worms will adapt.
• Must co-exist with the parasites, they are not going
away.
• Lambs/kids are the weak link, most susceptible to
parasite infections. In a pasture system, lamb and
kid management is labor intensive.
• Dry ewes/does have good level of resistance to
parasite infections and require low level of
management.
• Option: minimize lamb/kid time on the farm or on
pasture.

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Hemonchus
Telodorsagia
(Ostertagia)
Trichostrongylus
Cooperia
Nematodirus
About one-half inch

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Referred to as
“L3”

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egg to L3 >3.5 days
L3 to eggs in feces – 19 to 21 days
complete cycle – 24 to 25 days
L3s tolerate cold well

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Haemonchus contortus will survive
• Adult female can produce 5000 eggs per
day
• If each animal has 500 female worms
• 50 animals can contaminate your pastures
with approximately 1 billion eggs per
week!

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On Farm Research:Lessons Learned
• Lambs/kids are very susceptible to parasite
infections
• Overwintered larvae must be considered
• Making more than one grazing pass across
grass/legume paddocks with lambs/kids has the
potential to significantly increase the worm load
• Lambs/kids need some “safe” pastures

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• Farm #1
– All dewormed 7/20/06
– Rotated across previously
grazed pastures
 Farm #2
 All dewormed 7/16/06
 Moved to clean pasture every
week
Factors influencing FEC counts: Pasture
Management Matters
Lamb ID Sire ID FAMACHA FEC Lamb ID Sire ID FAMACHA FEC
603 A 3 300 11 B 2 0
612 A 3 0 14 B 2 0
613 A 1 250 46 B 1 0
616 A 3 1100 5 B 1 50
638 A 2 300 10 B 1 0
639 A 3 500 49 B 1 0
640 A 3 3450 6 B 3 50
641 A 3 1800 24 B 2 0
645 A 3 250 29 B 2 150
646 A 3 3150 3 B 2 0
Sire A Average 3 1110 Sire B Average 2 25
Farm #2 - 8/19/06Farm #1 - 8/16/06

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What is safe pasture for lambs?
• Young lambs/kids do not have a developed immune
system, any infective L3 larvae they ingest will get
multiplied!
• One where L3 larva concentration is low: managed
so that minimal levels of L3 are ingested.
• One where no L3 larvae have survived: a long
enough time period has passed that L3 larvae have
died. How long? Over-wintered larvae?
• One that limits grazing height/How does grazing
height influence parasite infection?

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Based on farm research results:
• Over wintered larvae are a concern. Spring grazing
(April/May) of pastures that were used the previous
fall (Sept./October) increases the risk of parasite
infection.
• Lamb/kid nutrition on pasture is a challenge.
Nutrition is an important component of parasite
management.
• There needs to be an effective chemical de-wormer
that can be used selectively and as a rescue
treatment.

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Possible alternatives to
preserve a refugia
• treat selectively with FAMACHA, or body
condition score; then move
• leave heaviest 10-15% untreated; then
move
• treat all animals with a non-persistent
dewormer and leave on contaminated
pastures 3-5 days
• move, wait a few days, then treat

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Concept Behind Selective Treatment
• Every animal in the flock does not have the same
parasite numbers/level of infection
• 20-30 % of animals harbor most of worms,
responsible for most of egg output
• Selective treatment targets these animals only
• Tools:
– FAMACHA
– Fecal Egg Counts?

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XXX Farm Daily Egg Output
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46
all sheep
numberofeggs
103,546,200 eggs per day
for just 46 sheep
Just 10 (21%) of the lambs
excreted 77% of the eggs !!
Fall 2000

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600 epg
50 epg
1150 epg
3150 epg
100 epg
1150 epg
0 epg
1050 epg
5550 epg
0 epg

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The FAMACHA© System
• Eye color is correlated with the
level of anemia, and to a lesser
degree, fecal egg shedding
levels
• Eye color is an indirect
measure of the worm burden –
applies to Hemonchus
contortus ONLY

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• By selecting only the most heavily infected
animals for treatment, we can significantly
reduce the number of treated animals while
still reducing pasture contamination and
providing treatment to the animals that need it
most.
XXX Farm Daily Egg Output
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46
all sheep
numberofeggs
This approach should
slow the development of
resistance to dewormers.
Refugia

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• current recommendations are to treat:
– non-lactating ewes in categories 4 and 5
– lactating ewes and lambs in category 3, 4, or
5 should be treated
– goats in categories 3, 4 and 5
– all animals with “bottle jaw”

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FAMACHA
• In Ohio, the parasite life cycle begins to ramp up
in May.
• Animals should be scored beginning in May.
• If FAMACHA is the only strategy employed, it
must be done at least every 14 days, or more
frequently, by mid-June.
• It can be used in large flocks, by examining
subsets of animals.

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How not to do it !!!

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Always use the card !!!

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score 5/5/08 6/5/08 6/23/08 7/8/08
1 0.77 0.36 0.29 0.09
2 0.23 0.64 0.65 0.42
3 0.00 0.00 0.05 0.42
4 0.00 0.00 0.02 0.05
5 0.00 0.00 0.00 0.02
FAMACHA percentages over time
FAMACHA scores by group and over time -
2008
early
weaned

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FAMACHA correlation with FEC is good but not
perfect
FAMACHA average median range in
number Score FEC FEC FEC
10 2 6,930 6,000 1,100 to 15,000
30 3 9,998 7,925 2,000 to 26,000
19 4 20,120 19,100 6,000 to 35,000
59 lambs scored and sampled July 4, 2011

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FAMACHA Limitations
• Requires some type of handling
system
• Labor intensive
• Can disrupt grazing rotations
• Needs a record keeping system
that can track trends
• Extends effectiveness of
chemicals but does not eliminate
resistance already present
• Limited to Haemonchus
contortus detection

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But wait, I heard that Garlic works as a
dewormer…..
• Where is the information coming from?
• How was it evaluated? Cause and effect are not
so easy, there can be confounding factors.
Nutrition is one.
• To have confidence, should be the result of
scientifically designed and replicated studies.
This includes control groups and statistical
analysis.

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literature review/results of designed studies
• Diatomaceous earth (DE): No scientific evidence
• Copper Oxide Wire Particles (COWP):yes, some trials
indicate effectiveness. Should be used under veterinarian
supervision. However: potential toxicity, this is extra label
use, and effectiveness may be limited.
• Garlic: No
• Sericea lespedeza pellets: Some trials indicate effectiveness,
but possible nutrition effect?
• Papaya seeds: No
• Wormwood species: Artemisia absinthium in some trials
showed some positive effects
• Others???

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Resources
• OSE Veterinary Extension – Decision making
support tool
– http://vet.osu.edu/extension/decision-tree
• OSU Veterinary Extension Fact Sheets
– http://vet.osu.edu/extension/beef-sheep-resources
• OSUE - Small Ruminant Pastures, Parasites,
and Profits: Putting it all together – three 90
minute programs
•http://vet.osu.edu/extension/sare/parasite_control Scroll
down to mid page

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Additional Resources
– University of Maryland Extension:
http://www.sheepandgoat.com/ click on parasites heading
• American Consortium for small Ruminant
Parasite Control
• http://www.wormx.info/index.html

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Animal Health Regulations
• USDA-National Organic Program
http://www.ams.usda.gov/AMSv1.0/nop
http://www.ams.usda.gov/AMSv1.0/nopgeninfo
• Food Animal Residue Avoidance Database
http://www.farad.org/
• U.S. Food and Drug Administration
http://www.fda.gov/
http://www.fda.gov/AnimalVeterinary/default.htm
• FDA Requirements:
– Use of unlicensed drug is prohibited
– Veterinary Client - Patient Relationship
– Producer must not administer drugs in violation of FDA guidelines

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Conclusion
• Currently there is not an easy answer to internal parasite
control.
• Each farm must use various “tools” to put together a
integrated parasite control strategy + monitoring program
• The management strategy on your farm depends upon your
goals, your market and the size of your flock
• Recognize economic factors. Pasture is the cheapest feed.
Grains are expensive. Indoor facilities are costly, require
more labor and a manure management plan.

Internal Parasite Management in Pasture-Based Sheep

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