Large strongyles, particularly Strongylus vulgaris, were once a leading cause of fatal colic in horses. While decades of interval-based worming dramatically reduced cases, a shift towards targeted treatment—combined with increased international horse movement—has raised the risk of reintroduction.
Worm egg counts remain one of the most valuable tools for strategic worm control, but they cannot distinguish between small and large redworm eggs under the microscope. This has not posed a problem while large redworm infections were rare. However, the potential severity of disease caused by large strongyles means that any detection would alter the treatment approach significantly.
In small redworm infections, low egg counts are often left untreated to help reduce selection pressure for resistance. However, because large strongyles can cause life-threatening damage even in small numbers, any presence would warrant treatment with a suitable anthelmintic.
To support informed decision-making, Westgate Labs, are now offering a large strongyle larval culture test to enable specific screening for this parasite. The test fills a critical diagnostic gap by incubating faecal samples to hatch strongyle eggs, allowing identification of larvae by species. This enables targeted treatment decisions without relying on blanket worming, which can drive resistance in other parasites.
Professor Jacqui Matthews, BVMS PhD FRSE FRCVS, RCVS Recognised Specialist in Parasitology commented:
“The launch of a commercial larval culture test for large strongyles is a very timely and important step for equine health in the UK. While Strongylus vulgaris was once considered under control, recent published reports on its increasing prevalence from across Europe and growing concerns about the risk of clinical disease in the UK, highlight the urgent need for this service.
The move towards targeted worming is vital for preserving drug efficacy, but it must be backed by robust diagnostics to ensure we’re not leaving susceptible horses exposed to potentially life-threatening infections. Having access to an easy-to-use test that differentiates between small and large strongyles is a significant advancement and will support both effective treatment decisions and responsible parasite control.”
The test gives vets, prescribers, and horse owners a way to screen for large strongyles without returning to blanket worming—helping to safeguard horse health and preserve the long-term efficacy of wormers. It can be used on individual or pooled faecal samples (up to four horses), with results returned within two weeks. A risk based approach should be applied to testing, particularly for studs, properties with frequent horse movements and horses on minimal or selective worming schedules.
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