May 2026 – Coccidiosis in Calves

Coccidiosis is a parasite disease usually affecting calves between 3 weeks to 9 months old which causes diarrhoea/scour, dehydration, straining and a loss of condition. They develop immunity to the parasite, so it rarely affects older cattle.

The disease is spread through oocysts (eggs) in the dung and calves are infected when they ingest these oocysts in the environment. It thrives in damp, warm conditions such as wet bedding but can also be found in soil and on pastures, particularly the wet areas around water troughs. Birds don’t transmit the disease to cattle but rather it can quickly spread through a group of calves when animals drink water or eat feed out of troughs dirtied by manure.

The oocysts can survive in the environment for long periods of time (at least a year) in housing and on pastures. Cleaning and disinfection of the shed once animals are out to pasture can help prevent outbreaks in the following year. Use a disinfectant that is targeted at coccidia, as not all disinfectants are effective. Remove all organic material from the shed when washing before disinfecting or the disinfectant won’t be effective. If last year there was an outbreak in calves in a specific pasture, consider that field a high-risk for this year’s calves and rather place the calves elsewhere if possible. Using alternating ‘calf pastures’ from year to year can help reduce infection between calf crops.

The first priority for scouring calves is to isolate them from healthy animals in a clean, warm environment. Give one to two extra feeds of a good quality oral rehydration solution (2 litres) and continue to offer milk if they will drink or leave them with their dam if they are suckler calves. Cold and dehydration are two major risks to sick calves, so replacing fluids and salts lost from the diarrhoea is vital.

There are medicines that can be used to prevent clinical disease in the early stage of infection but they don’t always have a large effect once the scour has already started. These are used during high-risk periods, particularly if there have been outbreaks at specific times on the farm before. Speak to your veterinary practitioner on the best treatment plan for your herd.

There are a number of possible causes of scour in calves, so sampling can help with a diagnosis leading to more effective treatment and prevention. If you have scour in the calves, take faecal samples from sick and healthy calves in the group for the best chance of detecting the oocysts and rule out other causes.