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Coccidiosis and Bacterial Scours

Scours in young sheep

The four primary causes of scours in young sheep are worms, the protozoan Coccidia, and the bacteria Campylobacter and Yersinia. Nutrition can be involved, especially if there has been sudden changes in diet or a fast introduction to lush spring pastures, and nitrate toxicity – for example, in capeweed – will cause scours.

All causes of scours in young sheep are often secondary to some form of stress – transport, severe weather, concurrent worm burdens or infections, overstocking, poor or changed feed etc.

Bacterial enteritis

It’s easy to assume young sheep with diarrhoea have a heavy worm burden. But often the problem occurs not long after drenching/weaning and in these cases, bacterial enteritis caused by Campylobacter and Yersinia is a common diagnosis.

Yersiniosis occurs when susceptible lambs, 12 months or younger, eat feed or drinking water contaminated by the faeces of infected sheep (the organism can be present in the gut of apparently healthy sheep).

Campylobacteriosis is frequently diagnosed in weaners 3 to 9 months of age, especially during wet summers. Healthy lambs on good pastures will often recover without treatment, but in stressed malnourished lambs, high death rates are possible. As with Yersinia, the organism often occurs in healthy carrier sheep.

Less commonly, Salmonella will cause outbreaks of enteritis in lambs.

Diagnosis and treatment

Faecal egg counts are important as a first step in eliminating worms and coccidiosis as the primary cause of diarrhoea. It is then possible to have faecal samples from scouring lambs cultured in the laboratory to help identify the organisms involved, but this takes time and is most useful in flocks not responding to treatment.

If bacterial enteritis is suspected, we initiate treatment with oral sulphonamides or injectable antibiotics. If over 50% of the flock are affected, we recommend treating the entire flock. If under 50%, we may advise drafting and isolating affected lambs. If possible, they should be run at a lower stocking rate on better pastures with supplementary feed.


Young lambs under 6 months old are most at risk of coccidiosis. It is most often a secondary disease, and factors contributing to susceptibility include other causes of scours, high worm burden, high stocking rates and intensive feeding, feedlots, stress from transport, diet changes or severe weather, and contamination of the environment with oocysts from carrier ewes or other lambs.

Post recovery, lambs will usually develop solid immunity.


Lambs with coccidiosis present with diarrhoea (sometimes showing blood), high temperature, poor appetite, weight loss, anaemia and sometimes, death.

The coccidial oocysts are readily identified in faecal samples. Care needs to be taken with diagnosis as oocysts are present in the faeces of sheep of all ages. Normally we look for a very high oocyst count combined with typical symptoms of the disease in susceptible lambs.

Treatment and control

Sulphadimidine-based medications are the drugs of choice for coccidiosis. Treatment does not completely rid the sheep of the protozoa, but it reduces significantly the severity and incidence of the disease.

Prevention is important. Avoid putting lambs under the stressful situations mentioned above – poor nutrition, worm burdens, overcrowding etc.

Supplementary feed and water supply should be high enough off the ground to avoid faecal contamination where possible.

In groups of lambs at pasture, the frequent rotation of pastures for parasite control will also help control coccidial infection.