Large Strongyle Infections in Donkeys: Arterial Damage, Colic, and Parasite Control

Large strongyle infections are intestinal parasite infections caused by equine bloodworms, including Strongylus vulgaris, S. edentatus, and S. equinus. Donkeys become infected by eating infective larvae on pasture, hay, feed, or water contaminated with manure. Like horses, donkeys can carry these parasites with few outward signs at first.

The biggest concern is not only the adult worms in the large intestine. Immature larvae migrate through tissues and blood vessels before returning to the gut. Strongylus vulgaris is especially important because it can damage the cranial mesenteric artery and its branches, the vessels that supply much of the intestine. That damage can reduce blood flow and set the stage for painful, sometimes life-threatening colic.

Some donkeys show vague signs for weeks or months, including weight loss, poor coat quality, low energy, or mild recurring belly pain. Others are not recognized until they develop a more urgent problem. Because fecal testing does not show the migrating larval stages, a normal-looking manure result does not fully rule out risk.

The good news is that large strongyles are far less common in well-managed equine groups than they once were. Still, they remain important because missed infections can cause serious intestinal and arterial injury, and parasite control plans that rely on routine deworming alone may not work well if drug resistance is present.

Large strongyle infections start when a donkey swallows infective larvae from contaminated pasture or feed. Eggs passed in manure hatch and develop outside the body, then climb onto grass where they are eaten during grazing. Warm, moist conditions and heavy pasture contamination help the cycle continue.

After ingestion, the larvae do more than stay in the gut. They migrate through tissues, and in the case of Strongylus vulgaris, through arteries that supply the intestines. This migration can inflame and thicken the vessel wall, encourage clot formation, and reduce blood flow to parts of the bowel. That is why some donkeys develop colic even when the number of adult worms in the intestine does not seem dramatic.

Risk rises when manure builds up in turnout areas, stocking density is high, new animals are added without a parasite plan, or dewormers are used on a fixed schedule without testing whether they still work. Resistance among equine strongyles has been reported for all major dewormer classes, so repeated treatment does not always mean effective control.

Donkeys living with horses, mules, or other equids share parasite exposure. Age, immune status, pasture management, and local climate all influence risk. Some donkeys may also appear healthy while still contributing eggs to the environment, which is why herd-level planning matters.

Diagnosis usually starts with your vet's exam, your donkey's history, and a discussion of pasture use, deworming history, manure management, and whether other equids on the property have had parasite problems or colic. If your donkey is painful, the first priority is stabilizing the colic and deciding whether emergency referral is needed.

A fecal egg count is commonly used to measure strongyle egg shedding and help guide parasite control. This test is useful, but it has limits. It does not detect immature or migrating larval stages, and routine egg morphology cannot reliably distinguish large strongyles from small strongyles. In some cases, your vet may recommend larval culture, repeat fecal testing, or a fecal egg count reduction test to see whether the chosen dewormer is still effective on your farm.

Bloodwork may be used to look for anemia, inflammation, dehydration, or changes linked with intestinal injury. In donkeys with significant colic, your vet may also recommend abdominal ultrasound, rectal examination when appropriate and safe, nasogastric intubation, or referral for hospital-level monitoring. These tests do not diagnose large strongyles by themselves, but they help identify how serious the intestinal problem is.

Because migrating larvae can damage arteries before fecal results become very informative, diagnosis is often a combination of evidence rather than one single test. Your vet may make a working diagnosis based on compatible signs, parasite risk, and response to treatment while also ruling out other causes of colic, weight loss, or diarrhea.

Prevention works best when it is planned, not automatic. Modern equine parasite control relies on fecal egg counts, targeted treatment of higher shedders, and periodic checks that dewormers are still working. Expert guidelines no longer support deworming every equid on a fixed year-round schedule without testing, because that approach can speed resistance.

Work with your vet to build a donkey-specific plan. That usually includes fecal egg counts once or twice yearly in adults, strategic baseline treatments to help control parasites such as large strongyles, and fecal egg count reduction testing when resistance is a concern. Keep in mind that fecal egg counts help measure shedding, but they do not detect migrating large strongyle larvae, so your vet may still recommend treatment at key times even in a low shedder.

Pasture hygiene matters. Remove manure from paddocks regularly, avoid overcrowding, reduce overgrazing, and quarantine or test new arrivals before mixing them with the herd. Feeding off the ground when possible and keeping water and hay away from manure-contaminated areas can also lower exposure.

Finally, think herd-wide. Donkeys, horses, and mules sharing space can share parasites. A prevention plan is strongest when every equid on the property is considered, records are kept, and changes are made based on testing rather than guesswork. That approach supports both parasite control and long-term dewormer usefulness.