Over the past year, many sheep farmers across the UK encountered Haemonchus contortus (barber’s pole worm) for the first time. Once considered a parasite largely confined to warmer climates, it is now emerging as one of the most significant and challenging health threats to sheep flocks in our region.
As we move into 2026, understanding this parasite and adapting how we manage it will be critical for flock health and productivity
Understanding Haemonchus contortus
Haemonchus contortus is a blood-feeding roundworm that lives in the abomasum. Its impact comes from both the damage it causes and how quickly it can multiply.
Each worm can ingest up to 0.05 ml of blood per day, so a sheep carrying around 5,000 worms could lose approximately 250 ml of blood daily. This blood loss leads to anaemia, weakness, and potentially collapse or death if left untreated.
At the same time, the parasite reproduces rapidly. Each adult female can produce between 5,000 and 15,000 eggs per day, allowing pasture contamination and infection pressure to build very quickly under the right conditions.
Unlike many other parasites, adult sheep do not develop strong immunity, meaning all age groups are at risk.
There is also increasing evidence that Haemonchus is adapting to survive across a wider range of temperatures, likely linked to climate change. As a result, risk is no longer confined to traditional summer peaks, and vigilance may be needed over a longer period of the year.
Recognising Clinical Signs
Haemonchus presents different to more familiar worm burdens, which can make it harder to detect.
Most importantly, diarrhoea is not normally seen.
Instead, signs are linked to blood loss and anaemia:
- Pale mucous membranes (particularly the lower eyelid)
- Lethargy and weakness
- Reduced performance
In more advanced or chronic cases:
- Animals may lose condition
- Fluid swelling under the jaw (“bottle jaw”) can develop
Severe cases may result in sudden collapse or death.
Monitoring Haemonchus on Farm:
- Worm Egg Counts
Regular worm egg counts should be carried out to assess worm burden. Haemonchus usually presents with exceptionally high worm egg counts
- Body Condition Score
Regularly body condition score or weigh animals to identify weight loss as early as possible
- Eye Colour: FAMACHA Scoring – A Useful On-Farm Tool
Because anaemia is the key clinical sign, FAMACHA scoring is becoming an increasingly valuable tool for monitoring.
This system involves examining the colour of the eye membrane. This can be scored with the FAMACHA© system from 1 (normal pink colour) to 5 (white indicating severe anaemia).
Used correctly, FAMACHA can help:
- Identify at-risk animals early
- Support targeted selective treatment (TST)
- Reduce unnecessary use of wormers
Treating Haemonchus on Farm:
As treatment decisions around Haemonchus become more complex, there is growing emphasis on responsible and evidence-based wormer use. Blanket treatments are unlikely to be sustainable, particularly given the already significant concerns around anthelmintic resistance within UK flocks. Targeted selective treatment (TST), supported by tools such as FAMACHA scoring, weight monitoring, and worm egg counts, should form the cornerstone of modern control strategies. In practice, this means selecting and treating only those animals that genuinely require intervention, while leaving a proportion of the flock untreated to maintain refugia and slow resistance development.
For those wanting to deepen their understanding, the RUMA webinar “Haemonchus: The Challenge of Treatment Decisions” provides an excellent, practical overview of current thinking. It explores how to balance animal welfare, productivity, and responsible medicine use in the face of this emerging parasite threat. We would strongly encourage farmers and shepherds to engage with this kind of training as part of their ongoing flock health planning. To book your FREE tickets, sign up HERE! As a practice, we are also happy to support interpretation and application of these principles on-farm.
Key Take-Home Messages
Haemonchus contortus is becoming an increasingly relevant parasite for UK sheep flocks, with the potential to cause rapid and severe disease. The challenge lies in its ability to build quickly, present without obvious signs such as diarrhoea, and affect animals of all ages.
Early recognition of anaemia, rather than relying on traditional indicators, is critical. Regular monitoring and a more targeted approach to treatment will be essential to managing risk effectively.
Give us a call or pop into practice to chat about reviewing your parasite control plan or arranging FAMACHA training ahead of the season.
