Strongyle infection

Veterinary advice should be sought before applying any treatment or vaccine.

Strongyle Infection

Bloodworms, Strongylosis

Strongyle nematodes from the Strongylida suborder, referred to often as "large strongyles", are one of the most significant gastrointestinal parasites in horses worldwide. The three most common large strongyles that affect horses are Strongylus edentatus, S. equinus, and S. vulgaris. While living inside of the horse's GI system, they will produce eggs that get passed from the horse via feces. While living in the feces, the eggs will start to develop and turn into infective third-stage larvae and contaminate the environment surrounding the feces. Either the same horse, or other horses that graze on the same pasture may ingest the larvae while grazing. Once ingested, the strongyle larvae migrate to specific organs within the horse's body; each strongyle species has a preference for specific organs. For example, S. vulgaris are usually found in the horse's vascular system, S. edentatus in the liver and retroperitoneum, and S. equinus in the liver and pancreas. Thromboembolic colic is caused by migration of larval stages of S. vulgaris.


Poor performance
Recurring colic
Dull or rough hair coat
Pot belly
Stunted growth
Weight loss


  • History
  • Fecal exam



Deworming through the implementation of a barn-wide program. See Recommended Deworming Schedule


  • Rotate pastures, if possible
  • Regularly remove horse manure from pastures
  • Do not overcrowd pastures with too many horses.
  • Harrow pastures only during hot, dry periods and keep horses off for several weeks
  • Rotate cattle, sheep or goats into pastures previously occupied by horses, since the larvae becomes inactivated when consumed by other species.
  • Compost manure
  • Feed horses in buckets as opposed to off the ground.
  • Promptly clean up manure from areas where horses are thrown hay to eat during the winter, or provide hay in a large container, slow feeder, or hay net.
  • Group pastures according to age, to reduce exposure to younger horses.

Scientific Research

General Overviews

Risk Factors

  • Not removing horse manures from pastures, especially in small paddocks and/or where horses may frequently be thrown hay to consume
  • Not conducting annual fecal testing
  • Multiple horses kept on the same pasture