Strongyles – There are 34 different species

Strongyles are responsible for the most damage to horses caused by any parasites. There are over 34 species of strongyles divided basically into 2 groups. The large strongyle group has been the most damaging until recently. The education of horse people concerning internal parasites over the last 50 years and the development of new more effective deworming medications has tremendously reduced the harmful effects of strongyles in the horse industry. However, the prolific nature of the worms has allowed them to withstand the effects of these deworming medications. Some horses pass as many as 5000 strongyle eggs/gram of stool. A drop of dew taken from a blade of grass in a pasture may contain as many as 100 infective larva.

Some studies have indicated that 80%-90% of colic in horses are caused by strongyles. Both large and small strongyles have been proven to cause colic. The larva stages of large strongyles migrate throughout many tissues in the body of the horse such as liver, arteries, and intestinal lining. Small strongyle larva exist in the lining of intestine and cause colic when they exist in large numbers.

Large Strongyles

( migratory, Blood worms)

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Small Strongyles

(non- migratory, Cyathostomins)

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Specimen Photos/Illustrations