PARASITES AND DEWORMING YOUR HORSES Control vs. Eradication

Karen Kalck, DVM, DACVIMEquine MedicineUniversity of TennesseeVeterinary Medical Center

PLAN

•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• 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

•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

Roundworms (Ascarids)

Large Strongyles

Small Strongyles

Pinworms

Tapeworm

LIFECYCLE

Eggs

• Manure of infected horse• Ground

Larvae

• Immature worms• Stomach/intestines

Adults

• Mature worms passed in feces

Grazing eggs/larvae swallowed

Larvae migrate out of intestines, into other tissues, and then return to intestine

STRONGYLES

•Also known as bloodworms, red worms•Can cause anemia•Damage colon•Mesenteric arteritis (large only)

LARGE STRONGYLES

SM

ALL

STR

ON

GYLE

S

ROUNDWORMS

•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 “cement-like” 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

•Keep FEC low•Reduce transmission•Reduce the development of drug

resistance•Have happy, healthy horses•Kill adult parasites

NO!!!

DEWORMERS• Zimectri

n• Equimax• Eqvalan• Ivercare• Rotation

1

Ivermectin

• QuestMoxidectin

• Strongid T• Rotation 2

Pyrantel

pamoate

• Quest plus• Zimectrin

gold• Equimax

Praziquantel

• Panacur• Safe-

guard

Fenbendazole

• Anthelcide

Oxibendazole

DEWORMERS

StrongylesTape-worms

Round-worms

Pin-worms

Bots

Ivermectin / Moxidectin

X X X

Pyrantel pamoate

X X X

Oxibendazole X X X

Praziquantel X

Fenbendazole X X X

DAILY DEWORMER

•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

NU

MB

ER

OF

HO

RS

ES

FECAL EGG COUNT (per gram of feces)

LOW(50%)

MODERATE(30%)

HIGH(20%)

LOW CONTAMINATORS (< 200 epg)

•September Treat with Ivermectin-Praziquantel

•March Treat with Moxidectin-Praziquantel

OR

MODERATE CONTAMINATORS (200-500 epg)

•September Treat with Ivermectin-Praziquantel

•November Treat with oxibendazole and/or pyrantel (together)

•March Treat with Moxidectin-Praziquantel

OR

+

HIGH CONTAMINATORS (> 500 epg)

•September Treat with Ivermectin-Praziquantel

•November Treat with oxibendazole and/or pyrantel (together)

•December Treat with Moxidectin

•March Treat with Moxidectin-Praziquantel•

OR

+

DEWORMING:Strategic vs. Every 2 months

Classification # of horsesNumber of doses/year

Subtotal Grand total

Low 10 2 20

54Moderate 6 3 18

High 4 4 16

Every 2 mos. 20 6 120 120

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

•Manure management•Pasture rotation and management•Avoid over-stocking•Group horses by age•Feeders

EQUINE WELLNESS PROGRAMUT 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

▫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

▫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