Over the past few weeks, we are increasingly encountering cases of Haemonchus contortus, commonly known as the Barber’s Pole worm. This blood-sucking gastrointestinal parasite is becoming more prevalent due to changing weather patterns, particularly milder winters which allow the larvae to overwinter both on pasture and within ewes.
As we are also coming into dipping season it is essential that farmers understand the heavy risks of treating sheep with yellow wormer and dipping them in close proximity.
Understanding Haemonchus
Historically, harsh winters helped suppress Haemonchus populations, but recent climate shifts have created ideal conditions for the parasite to thrive. As a result, infections are now being seen throughout the year and in regions previously considered low-risk, including northern parts of the UK.
Haemonchus contortus resides in the true stomach of sheep, where it feeds on blood. Unlike other gastrointestinal worms, it does not cause scour, which often leads farmers to overlook its presence. Instead, it causes anaemia, which can be fatal if left untreated.
The worm’s lifecycle is rapid and prolific — females can lay up to 5,000 eggs per day, quickly contaminating pasture and increasing infection risk. Sheep ingest infective larvae while grazing, and depending on the burden, symptoms can range from subtle to severe.
Symptoms to Watch For
Haemonchus infections present in three forms:
- Acute infection: Sudden death, pale mucous membranes (visible in the lower eyelid and inner lips), and rapid breathing.
- Sub-acute infection: Bottle jaw (fluid swelling under the jaw), lethargy, and anaemia—often mistaken for liver fluke.
- Chronic infection: Poor body condition, weight loss, and general failure to thrive.
Because scour is absent, you may not notice the usual signs of worm burden. This makes regular monitoring essential.
Diagnosis and Monitoring
At Severn Edge Farm Vets we have a combination of tools to help you tackle Haemonchus:
- FAMACHA scoring: A simple colour chart used to assess anaemia by examining the lower eyelid.
- Faecal Egg Counts (FECs): Useful for identifying worm burdens, please contact the practice on 01746 713911 to discuss or simply pop in with your sample.
- Post-mortem examinations: Crucial in cases of sudden death or unexplained poor performance.
If Haemonchus is suspected, samples should be promptly brought into practice for testing so that we can provide you with the best treatment plan depending on your farm and needs.
Treatment Options
Haemonchus is generally susceptible to most broad-spectrum wormers, but resistance is an increasing concern. Products containing Closantel are often effective. However, treatment should be targeted, not blanket, to avoid accelerating anthelmintic resistance.
Veterinary advice is vital in selecting the right product and determining which animals need treatment.
A Critical Warning: Yellow Wormers and Dipping
One important safety note for veterinary practices to communicate is the danger of using yellow wormers (Levamisole) in close proximity to dipping sheep. Administering Levamisole within 14 days before or after dipping can be deadly.
This is due to the heightened immune response triggered by the ingredient in yellow wormer, which, when combined with the stress and chemical exposure from dipping (often involving organophosphates), can lead to severe reactions or death. The interaction is not fully understood, but the risk is significant enough that manufacturers and vets strongly advise strict separation between these treatments.
The symptoms of the toxic combination of Levamisole and sheep dipping are:
- Heightened immune response or neurotoxicity
- Respiratory distress
- Sudden death, especially in lambs or compromised animals
Best practice advise is to adhere to the following steps:
- Never use Levamisole within 14 days of dipping, this is before and after.
- Always check product labels and withhold periods.
- Avoid treating tired, wet, or stressed animals.
- If both treatments are needed, plan carefully and consult us if there is any confusion.
Prevention and Sustainable Control
Here at Severn Edge Farm Vets we promote evidence-based parasite control:
- Encourage quarantine and worming of incoming stock.
- Implement good pasture management, such as rotational grazing and avoiding heavily contaminated fields.
- Support nutritional monitoring, as lambs under stress are more susceptible to infection.
- Avoid unnecessary blanket treatments to reduce resistance risk.
Conclusion
Haemonchus contortus is no longer a southern-only problem. With its stealthy symptoms and deadly potential, it demands vigilance and informed action. Risks are extremely high when treating haemonchus during the same period as dipping your sheep; be aware and if in doubt ask us for advice. Through targeted monitoring, safe treatment practices, and sustainable control strategies, we can help protect your flocks and preserve the efficacy of vital worming products.
Call us on 01746 713911 to discuss treatment options, faecal egg counts and any questions you may have.
