By Heather Stevenson,

SAC Veterinary Services


As the days lengthen and the sun climbs in the sky, we can expect temperatures at pasture level to rise, but with this comes the risk of worm problems and first on that list for lambs is nematodirus battus.

Infection with nematodirus battus causes scour and death in lambs during late spring and early summer. Losses can be high and surviving lambs suffer a check in growth, with lambs aged six to 12 weeks most often affected.

The worms live in the intestines and eggs are passed in the dung. Affected lambs look tucked up, don’t suck, have a severe scour and may be found gathered around water troughs.

You can find nematodirus eggs in dung samples, but scour and death can occur before any eggs are passed. In these cases, diagnosis requires a post-mortem examination at your local SAC veterinary laboratory.

In order to hatch, nematodirus eggs like a period of cold weather followed by rising temperatures. This means that most eggs passed by lambs in spring won't hatch until the following spring.

When conditions are right it allows large numbers of eggs to hatch at the same time, posing a serious disease risk. Hatching dates vary with region but a disease forecasting map can be found at

Nematodirus eggs are capable of surviving for two years in soil. So fields where lambs have scoured due to nematodirus will be contaminated with high numbers of eggs and should ideally not be used for young lambs the following year.

By avoiding grazing lambs on the same fields every spring you will prevent a year on year build up of eggs and reduce the risk of nematodirus outbreaks.

Where there is a nematodirus risk, lambs can be dosed to try and prevent an outbreak, although local knowledge should be used to pick your timing. For example, in Scotland, nematodirus outbreaks are seen most commonly from mid-May to mid-June, but can occur early in April if the weather is favourable.

Nematodirus is a difficult worm to kill and drenching must be carried out accurately to avoid underdosing. Despite one report of resistance, white drenches (1-BZ, benzimidazole products) are the treatment of choice in most cases.

Not all wormers are suitable for treating nematodirus, so if you are unsure ask for advice on which product to use.

If lambs are scouring and don’t improve after treatment, collect dung samples so that the problem can be investigated. For example, infection with coccidiosis can cause problems in the same age group of lambs.