Dairy cow with coccidiosis

What to look for

  • Mild to serious diarrhoea in calves
  • In serious cases diarrhoea contains blood and, after a short period, smears their rear end
  • Animals look listless and may become dehydrated, go off their feed and have a rough coat
  • Recovery can be slow, especially if the affected calves stay in the same area and are continually being re-infected

Cause – a protozoan infection 

  • Most often caused by Eimeria zuernii or Eimeria bovis 

Animals likely to be affected

Usually young animals 3-8 months of age

Other diseases with similar signs

Other infectious causes of scours in calves:
Salmonella infection
Mucosal disease
Cryptosporidium infection
Intestinal parasites
Rotavirus infection
E coli infection

Confirming the diagnosis

Laboratory test for coccidia in faeces. If necessary confirm the diagnosis by conducting a post-mortem examination and observing the characteristic changes to the gut wall.

Spread of the disease

Coccidia are picked up while feeding and infect the cells that line the calf’s intestine. Large numbers of coccidia are then shed in the faeces. Environmental contamination can build up, so that animals can be constantly re-infected in areas that are continuously used for young stock, especially if stocking rates are high. The level of contamination is greater if there are moist conditions that favour survival of organisms in the environment.

Risks to people

No risks for people but other causes of diarrhoea in calves (such as salmonella infection) may cause disease in people.


The first step is to separate the sick animals. Other animals in the group should be moved from the contaminated area. Appropriate treatment can be prescribed by your vet. If animals are dehydrated, they also need to be supported with electrolyte solutions.

When contamination has built up, a short course of a coccidiostat may be needed to break the cycle of infection before moving the animals on to safer pastures. Coccidiostats can be included in calf feeds. This should be planned with your vet to choose the most effective drugs, optimise the effect and reduce costs.

It is not necessary to aim for complete freedom from contact with the causative organisms as some contact allows the animals to build up immunity – the challenge is to avoid a level of infection that will cause disease.

Risk factors

  • Build-up of high levels of organisms in yards and paddocks used by young stock. If possible, young animals should be rotated around a series of paddocks that avoid any contact with adult animals (a practice also recommended for control of Johne’s disease).
  • Stockfeeds containing anti-coccidial drugs are suddenly discontinued

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