Parasite Control in Horses

Common Signs of Internal Parasites

• Poor growth
• Weight Loss
• Decreased feed efficiency
• Colic
• Diarrhea
• Pneumonia
• Death

The amount of disease a horse will show due to parasites depends on three factors:

• Kind of parasite involved
• Number of parasites involved
• Host defenses. Young and debilitated horses are generally most susceptible to parasites

Do current management styles lead to increased parasite problems?

• High stocking density increases number of parasites a horse ingests
• Poor manure handling may increase exposure by spreading infective parasites over pasture

• Parasites are most successfully prevented in horses through a combination of management and therapeutic strategies
• Management
  • Decreasing infective parasites in environment
• Therapeutic
  • Deworming with anthelmintics at proper intervals

• Adequate pasture acreage
• Composting Manure
• Cleanliness
• Pasture Rotation
• Deep plowing and reseeding
• Mixed grazing (cattle and horses)

• Moving horses from old, infested pasture to one with a minimal number of infective parasite larvae
• Should deworm prior to moving animals
• Foals and young horses should go on the cleanest available pasture

• Purge dewormers
• Extended action dewormers
• Continously fed dewormers
  • Kill infective larvae as they are eaten. Can prevent larvae from entering horse’s system

• Large strongyle
• Small strongyle
• Ascarids
• Bots
• Stongyloides
• Pin worms

• "Blood worm"
• Causes thromboembolic colic
• Most significant parasite of horses
• Direct life cycle
• Larvae live in artery supplying the intestines. Blood clots form which cut off the blood supply to the gut

• Fecal flotation
• Necropsy

• Strongylus endentatus and Strongylus equinus
• Direct life cycle
• Live in gut wall of large intestine
• Cause damage to gut wall resulting in G.I. upset

• Many products are available, nearly all horse wormers are effective against adults in intestinal track.
• Ivermectin, mixodectin, and fenbendazole effective against migrating larvae

• Use effective wormers routinely
• Avoid overgrazing pastures
• Use clean pastures for young horses
• Pile and compost manure

• Parascaris equorum
• Disease of horses up to 2 years of age
• Direct lifecycle
• Larvea migrate through lungs where they can cause damage
• Build up in large numbers in small intestine

• Impaction colic - death
• Pneumonia
• Pot belly
• Unthrifty appearance
• Poor hair coat

• Good sanitation
• Eggs live in environment for many years,
• Avoid pasturing foals in the same pastures year after year

• Most common dewormers are effective against ascarids
• If a foals has a very heavy infection it should be wormed with less effective wormers to prevent colic

• Insects- Adult is a fly, larvae live in the horse stomach
• Flies lay eggs on hair, they hatch and migrate to stomach
• May cause stomach irritation and colic

• See eggs on hair and mane
• Gastroscopy
• Necropsy
• Knowing flies are in the area

• Because bots are insects, only products which have activity against insects will be effective
• Ivermectin and Moxidectin are effective
• Nits can be removed from hair before they hatch

• Adult pinworms adult lay their eggs around the anus
• These eggs cause irritation and horses will rub their tails causing broken tail hairs
• Controlled by all common dewormers

• Egg masses in perineal region
• Tail rubbing
• Eggs in feces (rarely)
• Adults in feces

• Thorough cleaning of stalls
• Fresh feed and water

• Stronglyoides westeri
• Infects young foals
• Larvae passed in mare’s milk to foals
• May cause diarrhea in young foals
• DOES NOT cause foal heat diarrhea

• Fecal exam for larvae
• Fecal culture

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