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Haemonchus contortus is a gut worm where the adults settle in the abomasum. Adult haemonchus worms have the ability to remove large quantities of blood (0.05ml/day) from their host. That means a sheep carrying 5,000 adult worms may lose 250ml of blood per day. This, combined with blood loss from the stomach lining due to ulceration, causes anaemia and risk of death. As few as 500 adult worms can cause disease. 

Haemonchus burdens on pasture can build up quickly as the life cycle of the worm (time from adult laying eggs in host to those eggs becoming laying adults) is 20 days and an adult can lay 5000-15000 eggs per day.  

The risk of haemonchus is ever growing due to climate change. Warm and wet conditions, especially after dry spells, create ideal conditions for haemonchus larvae to thrive on pasture. The season where animals are affected also appears to be extending, with more outbreaks occurring later in the autumn. There have also been reports of haemonchus overwintering on pasture, meaning burdens can remain from one year to the next. This means that if haemonchus is diagnosed on your farm you will need to be vigilant in future years.

Unlike most other gut worms, sheep do not build up immunity to haemonchus so adult ewes and rams are at risk and sampling of these should be considered to look for haemonchus when doing routine worm egg counts.

Animals with high haemonchus burdens can show the following signs:

• Weak animals that are likely to collapse if gathered
• Pale mucous membranes (around the eyes is a good place to look)
• Quick, shallow breathing and increased heart rate
• Scour/mucky back ends is not a typical sign
• Sudden death

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