What is Haemonchus?

Haemonchus contortus, also known as Barber’s Pole worm, is a gastrointestinal parasite that infects sheep. The worm lives in the abomasum (fourth stomach) and feeds on blood by attaching to the stomach lining.

Each worm can ingest up to 0.5ml of blood per day. In heavy infections, this can lead to significant blood loss — for example, an animal carrying 5,000 worms may lose up to 250ml of blood daily.

Sheep of all ages can be affected, and the severity of symptoms depends on the number of infective larvae ingested.

Clinical symptoms

The signs of infection depend on the level and duration of parasite exposure.

Acute infection

Ingestion of large numbers of infective larvae over a short period can lead to severe disease.

• Severe anaemia
• Lethargy
• Weakness
• Collapse in some animals
• Death if not treated promptly

Chronic infection

Smaller infections over a longer period can lead to more gradual signs:

• Loss of body condition progressing to emaciation
• Moderate anaemia
• Bottle jaw (fluid build-up under the jaw)

Diarrhoea is not typically associated with Haemonchus infection.

Areas and conditions of higher risk

Sheep grazing in environments with warm temperatures and high rainfall are generally at greater risk, as these conditions favour parasite survival and development.

However, the parasite has shown the ability to adapt and survive across a wider range of environmental conditions, meaning risk is no longer limited to traditional high-risk regions.

Haemonchus lifecycle

The lifecycle of Haemonchus is continuous under favourable conditions and relies on grazing patterns:

• Larvae develop into adult worms in the animal’s stomach
• Adult females lay up to 5,000 eggs per day
• Eggs pass out in faeces onto pasture
• Larvae hatch and develop on the ground
• Infective larvae migrate onto grass
• Grazing sheep ingest larvae and the cycle continues

Treatment and prevention

A proactive approach is essential to manage Haemonchus effectively and minimise its impact on flock performance.

• Carry out regular worm egg counts to assess worm burden
• Monitor body condition and weight to detect early changes
• Check for anaemia by examining the colour of the eye membrane
• Quarantine and treat incoming animals to avoid introducing infection
• Work with your vet to choose appropriate worming treatments

Haemonchus can be treated with many broad-spectrum wormers, as well as some narrow-spectrum products containing Closantel. Always consult with your vet or adviser to select the most suitable option.

How Herdwatch can help

Managing parasite risk depends on consistent monitoring and accurate records. Herdwatch helps simplify this by keeping everything in one place.

Track body condition and weights

Record body condition scores and weights in real time to identify early signs of weight loss or poor thrive, which may indicate parasite burden.

Keep medicine records organised

Log treatments, purchases, and usage instantly, so you always know what has been administered and when.

Manage pasture more effectively

Map your farm, add notes to fields, and identify grazing areas that may present a higher parasite risk.

Stay ahead of parasite challenges

Haemonchus can have a serious impact on flock health, but early detection and strong management can significantly reduce the risk. By combining regular monitoring, appropriate treatments, and accurate record keeping, farmers can protect flock performance and improve long-term outcomes.