Worms in Sheep

Worms present a significant production threat to sheep with infection costing the owners by significant financial loss. The main worms affecting sheep are stomach and gut worms, which are commonly termed roundworms or nematodes. Other worms that affect sheep are tapeworms (cestodes) and lungworms, which are found in the airways.

Common sheep worms and their effects;

  • Stomach and intestinal worms cause diarrhoea, appetite loss and weight loss
  • Lung worms cause coughing and unthriftiness
  • Barbers pole worm causes anaemia and bottle jaw due to blood sucking


In spring and early summer the parasites of most concern are coccidia and roundworms. Nematodirus effects lambs at 5-10 weeks especially if cold weather is followed by a warm spell .The other species  (Ostertagia and Trichostrongylus) usually effects lambs over 10 weeks,

Coccidia are caused by a small parasite called Eimeria that effects lambs from 3-8 weeks old. They get infected orally from water and feed troughs and contaminated bedding. They can also be at risk if stressed or are grazing after earlier born lambs.

Rroundworms causes depression in appetite ill-thrift that can even result in death if present in large numbers.  Those lambs that are effected sub-clinically fail to reach their true potential by reduced growth rate and unable to achieve the target finished weight resulting in financial loss.  As there are many different species of roundworm that can effect grazing sheep in Ireland it is very important to the level and type of worms present in a herd..

The level of infection of roundworms and coccidian can be ascertained by counting the number of eggs passed per gram of faeces. This is commonly referred to as a faecal egg count or FEC.

Fluke is not an issue in finished lambs due to the time frame of its life-cycle.