Horse parasite lifecycles | Safe-Guard Equine Dewormer with fenbendazole

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The lifecycle of Strongylus vulgaris in the horse generally begins by the horse ingesting 3rd stage larvae from its pasture, water buckets, or other stable areas that have been in contact with 1st and 2nd stage larvae dropped in the feces of infected horses. Adult Strongylus vulgaris parasites can cause blood loss in horses, and the larvae can cause damage to arteries that supply the intestinal tract arteries.

Image: Picture of horse with the different stages of parasite lifecycle

Image: Picture of horse with the different stages of parasite lifecycle

The cyathostome parasite life cycle can be broken down into three phases:

Pre-parasitic phase (on the pasture or paddock)
Encysted phase (in the horse)
Parasitic phase (in the horse)

Diagram: Intestine of horse infected with internal parasites

Cyathostome eggs being passed out of the horse in the feces initiates the Pre-parasitic phase. Larvae develop from the egg into 1st stage larvae (L1), 2nd stage larvae (L2) and then the 3rd stage larvae (L3), which is ingested by the horse as it grazes. This L3 is the infective larvae, and it is enclosed in the sheath of the L2.

The L3 exit the sheath in the small intestine and migrate to the cecum and colon. It is here the Early L3 (EL3) penetrate the mucosa and can become encysted. They continue to develop, and molt to become L4. The 4th stage large (L4) excysts, emerges into the gut lumen, and molts to the 5th stage larvae (L5). The L5 then mature into adults to lay eggs and the process begins anew. Hypobiosis can occur when survival conditions are unfavorable. However, larvae resume development with moderate temperatures and greener grass. Then large numbers of larvae excyst en masse. This can involve thousands to millions of larvae exploding out of the gut wall, causing severe damage to the intestinal mucosa.

Controlled efficacy studies have revealed that up to 75% of encysted small strongyles are early 3rd stage larvae (EL3), which can remain hypobiotic for up to three years. These EL3's must be eliminated to prevent the detrimental effects of acute and subclinical larval cyathostomosis.

Larval cyathostomosis can cause severe clinical signs and even death in extreme cases. Clinical signs include: listlessness, weakness, anorexia, recurring colic, diarrhea, weight loss, and peripheral edema.

Even in lesser numbers, the damage caused as encysted small strongyles synchronously emerge from mucosal cysts in the intestinal lining can reduce the ability to absorb nutrients, impacting general health and performance. Lesser numbers of parasites involved in Larval Cyathostomosis can cause subclinical signs, such as: decreased performance, poor feed utilization, dull hair coat and listlessness.

The optimal time to treat for Larval Cyathostomosis is prior to the mass eruption of larvae, not after the damage is already done. The climate and the region will dictate the grazing season and will affect the parasite's life cycle, as well as identify if transmission is seasonal or year-round.

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For the effective elimination of ascarids, strongyles, pinworms, and other horse parasites.