PARASITES AND DEWORMING
YOUR HORSES Control vs. Eradication
Karen Kalck, DVM, DACVIM
Equine Medicine
University of Tennessee
Veterinary Medical Center
PLAN
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Introduction
Signs of parasitism
Types of parasites
Dewormers
Diagnostics
Designing a deworming program
QUESTIONS
1.
Raise your hand if you deworm your
horse(s) every 2-3 months?
2.
Every 4-6 months?
3.
Once per year?
4. Whenever you remember to?
COMMONLY ASKED QUESTIONS
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What type of wormer should I use?
When should I worm my horse?
Should I rotate my wormers each time?
Should I use the same wormer all year long?
How often should I worm and when?
What are fecal egg counts and do I need to have these
done?
• How effective are feed through wormers?
• My horse is rubbing it's tail, is this because of worms?
COMMON PRACTICES
• Deworm 4 times per year
• Deworm 2 times per year, once after the first
frost and once after the first hay cutting
• Deworm all year with the same dewormer
• Rotate your dewormer each time
• Only deworm if your horse is thin and not
putting on weight
PARASITES vs. BACTERIA
• No replication of numbers within the host
• Life cycle
• No immunity to parasites
SIGNS OF PARASITISM
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None
Lethargy
Loss of appetite
Dull, rough haircoat
Tail rubbing and hair
loss
• Loss of
condition/weight
• Slow growth in young
horses
• Pot belly
• Coughing, nasal
discharge
• Diarrhea
• Colic
• Death
TYPES OF PARASITES
Large
strongyles
Small
strongyles
Roundworms
Tapeworms
Pinworms
Lungworms
Bots
Strongyloides
Large
Strongyles
Roundworms
(Ascarids)
Pinworms
Small
Strongyles
Tapeworm
LIFECYCLE
Eggs
• Manure of infected horse
• Ground
Grazing  eggs/larvae swallowed
• Immature worms
Larvae • Stomach/intestines
Larvae migrate out of intestines,
into other tissues, and then
return to intestine
Adults
• Mature worms passed in feces
STRONGYLES
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Also known as bloodworms, red worms
Can cause anemia
Damage colon
Mesenteric arteritis (large only)
LARGE STRONGYLES
SMALL STRONGYLES
ROUNDWORMS
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Ascarids
Young horses (<2 years)
Large  up to 15 inches in length!
Do not suck blood
Small intestinal obstruction
Can migrate through the lung, causing damage
and pneumonia
TAPEWORMS
• Affect the last part of the
small intestine and cecum
• Can cause ileal
impactions
• Eggs often not found in
the feces
PINWORMS
• Females deposit eggs around anus in a “cementlike” mixture
• This dries and cracks, causing
irritation
• “Rat-tail” appearance
BOTS
• Not worms, but fly
larvae
• Female flies lay eggs on
horse legs
• Horse ingests eggs
• Larvae hatch and
migrate
to the stomach
DIAGNOSTICS - Collection
• Collect fresh feces in ziplock bag
• Label with horse name and date
• Send/take to veterinary laboratory
• Herd  Collect individual samples on same day
DIAGNOSTICS
• Fecal float
▫ Good screening test for all parasites
▫ Does not quantify
• Fecal egg count (FEC)
▫ Not to be used for screening
▫ Will quantify numbers of eggs per gram of feces
▫ Only for strongyles and roundworms
CONTROL VS. ERADICATION
• Must encourage anthelmintic-sensitive worms in
population
• Do not want to become outnumbered by
resistant worms
GOAL = CONTROL
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Keep FEC low
Reduce transmission
Reduce the development of drug resistance
Have happy, healthy horses
Kill adult parasites  NO!!!
DEWORMERS
Ivermectin
• Zimectrin
• Equimax
• Eqvalan
• Ivercare
• Rotation 1
Pyrantel • Strongid T
pamoate • Rotation 2
• Quest plus
Praziquantel • Zimectrin gold
• Equimax
Moxidectin • Quest
Fenbendazole
Oxibendazole • Anthelcide
• Panacur
• Safe-guard
DEWORMERS
Strongyles
TapeRound- Pinworms worms worms
Ivermectin /
Moxidectin
X
Pyrantel
pamoate
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Oxibendazole
X
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X
Praziquantel
Fenbendazole
X
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X
Bots
X
DAILY DEWORMER
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Pyrantel tartrate (Strongid C)
Does not resolve existing infections
Not effective against tapeworms or bots
Resistance!
Only appropriate in very specific situations
DESIGNING A DEWORMING PROGRAM
• Do not deworm all horses every 8 weeks!
▫ High levels of drug resistance
▫ Biology of parasites has changed
▫ Different worm demographics from horse to horse
DESIGNING A DEWORMING PROGRAM
• New recommendations – strategic deworming
▫ Treat some horses more and others less
▫ Involves FEC
▫ Advantages
 Fewer deworming treatments
 Less drug resistance
 Better worm control
POSSIBLE DEWORMING PLAN
• First treatment in September
• Last treatment in March
• No further deworming until fall unless there is a
very cool, wet summer
POSSIBLE DEWORMING PLAN
• Determine which anthelmintics are working in
the herd
• September  Egg counts on all horses
• Categorize horses’ contaminative potential
▫ <200 epg = low contaminators
▫ 200- 500 epg = moderate contaminators
▫ > 500 = high contaminators
HYPOTHETICAL DISTRIBUTION OF
STRONGYLE EGG COUNTS IN A HORSE HERD
MODERATE
(30%)
NUMBER OF HORSES
LOW
(50%)
FECAL EGG COUNT
(per gram of feces)
HIGH
(20%)
LOW CONTAMINATORS
(< 200 epg)
• September  Treat with Ivermectin-Praziquantel
OR
• March  Treat with Moxidectin-Praziquantel
MODERATE CONTAMINATORS
(200-500 epg)
• September  Treat with Ivermectin-Praziquantel
OR
• November  Treat with oxibendazole and/or
pyrantel (together)
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• March  Treat with Moxidectin-Praziquantel
HIGH CONTAMINATORS
(> 500 epg)
• September  Treat with Ivermectin-Praziquantel
OR
• November  Treat with oxibendazole and/or
pyrantel (together)
+
• December  Treat with Moxidectin
• March  Treat with Moxidectin-Praziquantel
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DEWORMING:
Strategic vs. Every 2 months
Classification
# of horses
Number of
doses/year
Subtotal
Low
10
2
20
Moderate
6
3
18
High
4
4
16
Every 2 mos.
20
6
120
Grand total
54
120
DEWORMING IN FOALS/WEANLINGS
• Start at 2 months of age
• Deworm monthly
• Alternate pyrantel and ivermectin
• At 8 and 12 months give a product with
praziquantel as well
OR
ENVIRONMENTAL CONTROL
• Moisture
▫ Strongyle transmission occurs almost exclusively
on pasture
▫ Stall and dry-lots are negligible
• Season (in TN)
▫ Summer  lowest pasture infectivity
▫ Winter  cool enough to promote larval
persistence
ENVIRONMENTAL CONTROL
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Manure management
Pasture rotation and management
Avoid over-stocking
Group horses by age
Feeders
EQUINE WELLNESS PROGRAM
UT Equine Hospital and Field Services
• Comprehensive health care program for horses
▫ Pleasure horse
▫ Performance horse
• Yearly health care needs in one package
• Packages are a 20% discount from individual
pricing
• Eligible for additional discounts and benefits
• Sign-up beginning March 12th, 2011!
HORSE OWNERS CONFERENCE
• March 12th, 2011 @ 8 am
• At UT – Hollingsworth auditorium
• Topics
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Wellness program
Small pasture management
Fescue toxicosis
Foot care and diseases
Use of common medications in horses
Lameness examinations
• $28/person ($15 for additional family members)
• www.vet.utk.edu/continuing _ed
UTVMC OPEN HOUSE
• Saturday April 16, 2011 from 9 am – 4 pm
• Educational day for families
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Teddy Bear Clinic
Canine Parade of Breeds
Equine Parade of Breeds – including Amigo!
Farm Animals
Wildlife and Exotic Animals
Physical Therapy for Animals
• www.vet.utk.edu/openhouse
QUESTIONS??
• Thank you to Dr. Sharon Patton for providing
information and pictures