Diarrhoea, wasting and poor appetite are all signs of coccidiosis in calves, which is straightforward to treat but swift action is needed

Coccidiosis is a cause of diarrhoea in calves and lambs. The severity of effects ranges from fatal to subclinical. The risk of losing calves is reasonably low, but disease spreads quickly within a group and recovery from coccidiosis is protracted. In beef calves the major economic effect is stunting, leading to increased time to slaughter.

Typically in beef animals coccidiosis affects older calves (six to eight weeks old) rather than many other causes of scour, such as E. coli or rotavirus. The most common signs are diarrhoea, wasting and poor appetite. The scour is typically grey and pasty, often with flecks of fresh blood and mucus. In severe cases the diarrhoea can become profuse and calves become severely dehydrated. Reduced appetite quickly leads to a gaunt appearance in growing calves. Irritation can also lead to persistent straining, which can then lead to rectal prolapse. Calves with coccidiosis rarely have a fever.


A vet should be consulted in any case of calf scour. They often diagnose cocci based on history (age of the calf being particularly important) and the clinical signs. They may also take a dung sample to aid diagnosis, although the results of this can be variable. If a calf has died, they may opt to take post-mortem samples to confirm the diagnosis. Frequently, diagnosis is confirmed by a positive response to treatment as described below.


If coccidiosis is suspected, treatment is straightforward. As with any scouring calf, isolate them where possible. There are several oral coccidiocides on the market with the active ingredients diclazuril (Vecoxan), and toltrazuril (Baycox and Tolracol) and resistance doesn’t appear to be a problem in coccidia. The benefit of the latter is that their persistent activity means that just one treatment is needed, whereas diclazuril products may need to be repeated three weeks later. Dehydrated calves also require appropriate fluids — oral electrolyte products should be suitable and do not withhold milk. If the calf becomes very dehydrated a vet may need to administer IV fluids. Finally, as with any sick calf, nursing is key. As always, your vet should be your point of contact when dealing with any disease outbreak.


As coccidia are present in the gut of all adult cattle, eradication is not feasible or necessary. The focus should be on reducing the challenge faced by calves at an early age. In practical terms this means optimising hygiene:

– Keep calving pens well bedded and dry;

– Both feed and water troughs should be clean of dung contamination;

– Have a suitable space ready to isolate scouring calves;

– Calve in tight batches and don’t mix age groups — consider synchronisation and AI if feasible;

– In fields, reduce or eliminate access to standing water, including poached areas around water troughs;

– Supply mains water where available.

These principles hold true for lambs as well, although they suffer with different species of coccidia and there is no cross-infection between sheep and cattle.

Disinfection is also an important part of shed hygiene, although the eggs of coccidia are more resistant to disinfectants than other pathogens. The eggs persist for more than 12 months, so simply resting sheds or fields won’t avoid the calves being exposed. As ever, getting calves off to a good start with the appropriate dose of colostrum is vital.

If, despite taking sensible measures, the challenge is likely to be high, a prophylactic dose (of one of the coccidiocides mentioned above) can be given. The timing of this varies, but it is often given at six to eight weeks. Previous outbreaks of disease on a particular holding can also be used to estimate when future outbreaks will occur. Check the recommendation for each product, but often the treatment is given around one week into the risk period.

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