Coccidiosis is caused by single-celled parasites (not bacteria) known as coccidia. There are several species in cattle, not all of which cause disease. The species that cause disease are primarily found in the large intestine, and the diarrhoea results from damage to the cells lining it.

Coccidiosis is seen in animals up to two years old, and is particularly common in calves between three weeks and six months of age. Cattle become infected when placed in environments contaminated by older cattle or other infected calves. This can happen either indoors on bedding, or outdoors around drinking or feeding troughs. In order for the coccidial oocysts (the egg stage of the parasite) to become infective they require warmth and moisture.

Poor hygiene, high stocking density, poor health and poor nutrition will all contribute to a calf picking up the parasites and subsequent disease.


Symptoms are not always specific to coccidiosis.

  • Diarrhoea (often very watery)
  • Depression
  • Loss of appetite
  • Weight loss
  • Dysentery (passing blood stained faeces)

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