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Parasite Control in the Equine
Each horse should have a comprehensive deworming program developed in cooperation between the veterinarian and the horse owner. Many factors should be considered, such as age, use, environment, and health of the individual. Different ages of horses will be more susceptible to different types of parasites. Environmental factors would include the number of horses living on the property, whether or not they are grazing irrigated pasture, and what the parasite load of the pasture or other herd mates are. The parasite load of each individual is important to know because these animals will be more debilitated and susceptible to other health risks, as well as will need a different deworming protocol.
Usually a good place to start is by performing a yearly fecal floatation on each individual. Yearly testing will help to identify chronic shedders in the herd. Occasionally a blood may be needed if infection is suspected, but fecal floatation is negative. Many different species of equine parasites can live in the blood and encyst in muscle tissue for long periods of time.
Common classes of drugs frequently used in any effective deworming protocol should include:
Avermectins – This would include both paste and liquid forms of Ivermectin, Zimectrin
Gold, Equimax paste (Ivermectin/Praziquantel)
Benzimidazoles – These would include Fenbendazole (Panacur) paste, and Oxybendazole (Anthelcide) paste forms.
Pyrimidines – These would include Pyrantel (Strongid paste and Strongid C/2x preparations)
Rotation of dewormers, aids both in reduction of resistance to medications, and provides broad spectrum coverage against all classes of parasites. Manual reduction of the environmental parasite load is important to help break the life cycle and reduce reinfection. Manure should be removed from pastures weekly or they should be dragged. Paddocks and stalls should be picked daily. Pickings should be either hauled off or thinly spread to allow adequate exposure to sunlight. This will kill many forms of parasites. This should occur remote from where the horses are housed. Removal of manure will also aid in fly reduction. A reduction in flies will minimize the spread of Gastrophilus, an internal form of the bot fly. Attention should also be given to establishing proper drainage of all paddocks and pastures. There should always be an effort to minimize the grazing of wetlands also. In addition, all horses on the property should be dewormed with the same product on the same day.
All horse owners should be familiar with the common symptoms of parasite infestation in the horse. These include:
Colic – Due to impactions, enteritis, ulceration, or aneurisms in intestinal circulation
Diarrhea
Coughing/respiratory disease
Weight loss/unthriftiness
Dull hair coat/dermatitis
Tail rubbing (broken hairs and bare areas)
Conjunctivitis
Behavioral problems
Lethargy/depression
Common Equine Parasites
Small Intestine
Ascarids (Parascaris equorum) causes impactions
Thread worms (Strongyloides westeri) causes acute diarrhea in foals 1-3 weeks of age
Tape worms (Anoplocephala/Paranoplocephala)
Caecum/Colon
Blood worms – Large strongyles (Strongylus vulgaris and sp.) causes anemia, and larval migration causes fatal aneurysms in large intestinal circulation. Small strongyles cause general unthriftiness and can cause enteritis.
Tapeworms (Anoplocephala) cause generally non pathogenic ulceration/inflammation of the ileocecal valve.
Rectum
Pinworms (Oxyuris equi) cause pruritis (itching) of the anal and tail region, with resulting hair loss.
Stomach
Bot fly larvae (Gastrophilus sp) may cause ulcers, but rarely pathogenic
Stomach worms (Habronema sp) in adults can promote the development of gastritis and tumors. These cause “summer sores” or cutaneous granulomatous lesions.
Liver
Large Strongyle larva
Lungs
Thread worm (Strongyloides westeri) larval migration causes coughing/respiratory disease in foals
Eye
Stomach worms (Habronema sp.) cause ulcerative conjunctivitis or “summer sores” They produce yellow sulfer granules that cause corneal/conjunctival abrasions.
Ectoparasites
Lice – Biting and sucking lice.
Ticks – Some carry Babesia sp. which infest redblood cells, cause persistent fever, anemia, icterus and spelomegaly. Spinose ear ticks can cause head shaking and head tilt when they infest the inside of the ear.
Mites – Orbatid mite is the tapeworm host. Mites also cause dry, wet, tail, hock, and nodular mange.
Flies –Spread diseases by fomite transmission. Some flies have larval forms that infect the stomach of the horse, such as the Bot fly and Habronema. Bites from some flies can cause skin irritation, allergic conditions, pruritis and behavioral problems.
Mosquitos – Carry many mosquito borne diseases, such as Eastern, Western, Venezuelan and West Nile encephalitis. Also, bites can cause skin irritation, pruritis and behavioral problems. Some horses are extremely senstitive to the bites from Culicoides which target the ventral midline of horses with fair skin.
Generally, rotating deworming every 8-12 weeks and using an Ivermectin product or Equimax paste at least once in the spring and fall is adequate for most healthy adult horses. For those horses on a daily wormer, only twice yearly deworming with Equimax paste is needed. However, deworming protocols specifically for foals, pregnant mares, debilitated individuals and those carrying a parasite load may differ in requirements. Discuss these specifics with your veterinarian.
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