Teladorsagiosis in Sheep: Brown Stomach Worm Infection

Teladorsagiosis is a parasitic disease of sheep caused by Teladorsagia circumcincta, also called the brown stomach worm. This parasite lives in the abomasum, which is the sheep's true stomach. It is considered one of the more important gastrointestinal worms in sheep, especially in cooler, wetter, temperate regions.

The worms damage the stomach lining and interfere with normal acid production and digestion. Even when infection is not dramatic, sheep may eat less, convert feed poorly, and fail to gain as expected. In heavier burdens, lambs may develop scours, weight loss, and a rough, unthrifty appearance.

This infection can be frustrating because some sheep look only mildly affected while flock performance slips over time. Ewes around lambing may also shed more eggs onto pasture, increasing exposure for lambs. That is why your vet will usually look at both the individual sheep and the whole flock picture when deciding what to do next.

Teladorsagiosis happens when sheep ingest infective larvae while grazing contaminated pasture. Adult worms in the abomasum produce eggs that pass in manure. Under suitable moisture and temperature conditions, those eggs develop on pasture into larvae that are then eaten by other sheep.

This parasite tends to be more common in cooler areas with wet winters and temperate climates. Risk rises when sheep are stocked heavily, graze short pasture close to manure, or return repeatedly to contaminated paddocks. Young lambs are often more vulnerable because they have less immunity.

Another important factor is periparturient egg rise. Around late pregnancy and early lactation, ewes can shed more parasite eggs, which increases pasture contamination for lambs. Over time, routine whole-flock deworming without testing can also select for anthelmintic resistance, making control harder and causing treatments to work less reliably.

Your vet usually starts with the flock story: age group affected, pasture conditions, recent weather, body condition trends, scours, growth rates, and prior dewormer use. Because brown stomach worm signs overlap with other gastrointestinal parasites, diagnosis is often based on a combination of clinical findings and testing rather than one clue alone.

A fecal egg count is commonly used to estimate the burden of strongyle-type worms in the flock. The challenge is that strongyle eggs often look similar on flotation, so a routine fecal test may support a parasite diagnosis without proving Teladorsagia alone. In some cases, your vet may recommend larval culture, pooled sampling, or postmortem examination if losses are occurring.

If treatment failure is a concern, your vet may use a fecal egg count reduction test to see whether the chosen dewormer is still effective on your farm. This matters because resistance is increasingly common in small-ruminant parasites. Bloodwork is not always needed, but it may help assess dehydration, protein loss, or other illness when sheep are more severely affected.

Prevention works best when it combines pasture management, monitoring, and selective treatment. Routine calendar-based deworming alone is no longer enough on many farms because parasite resistance is so common. Your vet may recommend regular body condition scoring, manure checks, and strategic fecal egg counts to identify which sheep are contributing the most contamination.

Try to avoid overstocking and very short grazing, since sheep pick up more larvae close to the ground. Separating the most vulnerable groups, especially lambs, from heavily contaminated pasture can help. Ewes around lambing deserve extra attention because egg shedding often rises during this period.

A farm-specific parasite plan may also include culling chronic high shedders, improving nutrition, and using dewormers only when they are likely to help. Follow-up testing after treatment can show whether a product is still effective. That information is valuable, because preserving dewormer effectiveness is part of protecting the whole flock long term.