Diarrhoea in sheep(scours, daggy backsides)

If your sheep get diarrhoea, their daggy rear ends will be a very obvious sign, not just to you but to all the passers-by who look over your fence!  Diarrhoea or scours means that the sheep’s faeces are not the normal dark firm pea-like pellets but they are soft and because they don’t drop cleanly away they soil the wool round the anus and build up to form dags.  As the diarrhoea gets worse, the faeces become runny then watery or mucus-y and in the worst type of diarrhoea (dysentery) they are blood-stained.

There are many causes of diarrhoea – from infections with worms, viruses or bacteria to irritants in the pasture.

If the diarrhoea is severe or if it persists, the loss of nutrients and fluid into the intestine can soon lead to severe dehydration, weakness and eventually death.   Even mild diarrhoea over a period of time will lead to slowed growth in lambs and weight loss in adult sheep.  Another risk even with relatively mild forms of diarrhoea in late summer and autumn is that the dags will attract blowflies, leading to flystrike.

What are the causes of diarrhoea?  The most common cause is worms, but there are many other potential causes too.  Here is a list of some of the main causes:

Hand-reared lambs less than 1 month old see Scours in hand-reared animals

Lambs 1 to 4 months old

  • Gastrointestinal parasitism (worms)
  • Coccidiosis

Lambs 4 – 12 months old

  • Gastrointestinal parasitism (worms)
  • Yersiniosis

Sheep over 12 months old

  • Gastrointestinal parasitism (worms)
  • Johne’s disease
  • Mycotoxins or endophytes in pasture (late summer-autumn)
  • High pasture potassium or nitrates in pasture (spring)
  • Gastroenteric listeriosis
  • Salmonellosis

Here is a little more information about the more common causes of scours in sheep:


Worms are the most common cause of scours in sheep, particularly in young growing lambs.  Older sheep usually develop some age-resistance to worms, but in young sheep and in adult sheep if there is enough of a challenge or if they are stressed by another disease like Johne’s disease, worms in the intestine and sometimes in the stomach can reach huge numbers.  They will then cause growth checks or weight loss with severe diarrhoea, fluid and protein loss then death.

If you don’t have an effective worm control programme (and even if you think you do but your sheep are scouring or not doing well), it would be worth asking your vet to arrange worm egg counts on ten faecal samples.  If worms are the problem, an effective drench and perhaps management changes should fix the problem.  You will have to ensure you have an effective drenching programme in place to prevent the problem recurring.

If you can rule out worms as the cause, you will need your vet’s help.  He or she will need to know the background and environment of the sheep (their history) and then examine a few and maybe take samples of blood or faeces for laboratory testing.  If there is a big mob of sheep a post-mortem or two may be necessary.


There is another type of internal parasite called coccidia that can cause diarrhoea, usually in lambs up to 4 months old but lambs up to a year old can be affected.  Small unthrifty lambs are more susceptible than those that are well-grown.

Coccidia are tiny one-celled organisms that live in the lining of the intestine.  They can reach huge numbers causing severe dark brown/black diarrhoea.  Because the coccidia can erode the lining of the intestine there may be blood in the faeces.  The organisms thrive in warm moist conditions, and the disease they cause is coccidiosis.

Sometimes coccidiosis sweeps through the mob without causing too many problems, but if it’s severe, veterinary treatment is needed or affected sheep may die.  There are special drugs to treat the disease, and affected lambs should be treated then moved to new and better grazing and a clean water source.


There is another type of bacterium that causes diarrhoea, this time usually in lambs in their first winter.  The bacteria are Yersinia and they cause the disease yersiniosis.  This is usually a relatively minor transient disease causing only soft faeces for a week or so, but occasionally it is more severe and requires treatment with antibiotics.

Spring and autumn scours

When there is no other apparent cause and the lambs are on lush pasture in spring, scouring is often called “spring scours” and it has been linked to irritants in pasture, perhaps high potassium concentration, perhaps a high concentration of nitrates or sugars.

In late summer and autumn, there may be fungal toxins growing in the dead vegetable matter at the base of the pasture that can cause ill-thrift and diarrhoea.

If either of these conditions is the problem, moving sheep to different pasture may solve the problem, but it’s important to rule out other possible causes such as internal parasitism before using this “fall back” diagnosis, and if the problem persists, see your vet


Salmonellosis is not very common fortunately but when outbreaks occur they are very serious.  It’s a disease that causes sheep usually mature sheep to become very dull and fevered, they develop severe and blood-stained diarrhoea and if they are pregnant they abort.  Most affected sheep die unless they get antibiotic treatment at an early stage.

The disease spreads rapidly between sheep and there is a risk of infection of humans too, so handlers must take as many precautions as possible to prevent spread to themselves and to other humans and livestock.  Two of the most common types of salmonella to cause the problem are Salmonella Typhimurium and S. Brandenburg, and there is a vaccine available that helps prevent further outbreaks.  Because it’s such a severe disease antibiotic treatment by your vet is vital.