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2 months
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Pyrantel
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4 months
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Ivermectin
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6 months
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2 x Fenbendazole
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8 months
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Ivermectin
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10 months
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Pyrantel
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12 months
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Ivermectin
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Mares – deworm with Ivermectin within 24 hours after foaling.
New Horses to a herd – Keep off pasture for 7 days after deworming.
Deworm adult horses (older than 1 ½ years) with Moxidectin. Repeat in 10-12 weeks.
Deworm young horses (less than 1 ½ years) with 2x Fenbendazole for 5 consecutive days.
When deworming you horse, make sure their mouth is empty or dewormer can easily be spit out.
Environmental Management Recommendations
Lawns are areas that horses like to graze in a pasture and roughs are areas that horses prefer to defecate. The infective strongyle parasite is 15 times higher in roughs. Horses will avoid these rough areas for grazing as long as the pasture is not overgrazed. Hay can be supplemented to avoid overgrazing of a pasture. If your pasture does not have lawns and roughs, it is overgrazed and will have a higher parasite concentration.
Drag your pasture in the summer – it takes temperatures of 90 degrees Fahrenheit to kill parasite larvae. Keep horses off of dragged pastures for 4 weeks. Pasture rotation is recommended.
Do not drag your pasture in the spring or fall. This practice only aides in spreading the larvae which can over winter and be infective the following spring.
Removal of manure from pastures and paddocks is beneficial. Manure should be composted. The temperature must reach 90-140 degrees Fahrenheit to kill infective eggs and larvae. Only composted manure should be spread on pastures.
Delay turnout to pastures in the spring/summer. A few weeks at 90 degrees kills larvae. Limited pasture exposure minimizes parasite exposure.
Interesting Facts about Parasites in Horses
Strongyles – Eggs hatch in the manure at temperatures of 45– 85 degrees Fahrenheit. The larvae can be infective in as little as 3 days in warm temperatures and can remain infective for several weeks in cooler temperatures. No hatching of strongyle eggs or development of larvae occurs from November to March in Minnesota. The eggs are killed by freezing temperatures. The larvae on the other hand can over winter and be infective the following spring. Infective larvae can persist over winter and are especially adapted for our weather in Minnesota.
- Large Strongyles are well controlled in most deworming programs because of their simpler life cycle.
- Small Strongyles invade the mucosa lining of the large intestine where they form a protective shell and can remain for several years before emerging. They are now the most important equine parasite because of their ability to produce disease and survive deworming programs. Transmission of strongyles is almost totally through pastures. Fecal egg counts are primarily concerned with small strongyle eggs.
Tapeworms – Horses get these from eating mites on pasture. Minnesota has a very high prevalence of tapeworms in horses at 98%. Tapeworms can cause colic because of inflammation of the intestinal mucosa.
Bots – The larvae are infective 7 days after the eggs are laid on the horse’s hair by the Bot fly. The oral stage is about one month. The larvae migrate and spend 8-10 months in the stomach and intestine after being swallowed.
Roundworms - These are a problem in horses less than 1 ½ years old. Eggs can remain infective for 10 years in the environment. Horses develop immunity after 2 years of age.
Pinworms, Threadworms (Strongyloides) – these and many other internal parasites are controlled with the dewormers that we use in our effort to control the more dangerous parasites.
Parasites are becoming increasingly resistant to deworming. The most effective way to slow resistance is through responsible use of current deworming (anthelmintic) products. Please work with your veterinarian to set up the best deworming program for your horse.
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