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Coccidiosis is a perennial parasitic problem in growing lambs. It presents some difficulties in diagnosis, treatment and prevention – but good news could be around the corner. 

Lambs and calves surviving a bout of coccidiosis are very strongly immune afterwards, and do not become ill if challenged with the same species.

This means there could be scope to develop vaccines. These would be given before lambs and calves meet the coccidial parasites.

See also: Q&A: How to prevent and treat coccidiosis in calves 

Vaccines would reduce the amount of damage caused, as the immunity effectively bounces, or repels, the parasites off the lining of the gut.

There is good experimental work showing that exposing very young lambs (one to five days old) to coccidial parasites makes them much more resistant to later challenge.

In addition, live attenuated vaccines for coccidiosis are used commercially in poultry production.

There have been many recent advances in vaccine technology. Specific parts of the organism can be targeted, rather like the spike protein targeted in the recent successful Covid vaccination programme.

Farm Post Mortems is working on a project with the AHDB and Biotechnology and Biological Sciences Research Council (BBSRC). This aims to identify the parts of the coccidial parasites that might make good targets for vaccines.

We are looking for faecal samples (and carcasses if affected animals die) from any cases of coccidiosis in lambs and calves.

These samples will be used to figure out the genetic code and identify genes and proteins in the coccidia, which are important in helping the parasite to get into the gut.

If the immune system can recognise these targets before lambs become infected, we hope that infections will be much less severe.

If you have had an outbreak of coccidiosis confirmed by your vet and would like to help contribute to this project, please get in contact at ben@farmpostmortems.co.uk or 07899 950 372.

Coccidiosis, or cocci for short, is caused by small protozoan parasites (Eimeria species) that live in the large and small intestines, and damage it.

The coccidial parasites exist in very small numbers in the guts of ewes and cows during the winter.

The first few lambs born will consume small numbers of these parasites and multiply them up quickly in their guts.

They then pass out much larger numbers of parasites, which younger animals can eat, leading to severe damage and death.

This snowball effect is difficult to predict and treat in lambs because not all lambs are affected at the same time.

Animals generally look poor. They have scours, which may be bloody, and have a much-reduced daily liveweight gain. They have dull, starry coats (hair/wool is patchy and stands on end).

Cattle coccidia cannot infect lambs and vice versa. Birds cannot infect lambs or calves – this is a myth.

The different strains of coccidia only infect one species and do not transfer between different species.

Currently, the most common treatment is to give lambs an oral dose of a coccidiostat containing diclazuril or toltrazuril.

This stops the coccidial parasites multiplying in the guts and allows the lamb to recover. However, these treatments are only effective when the parasites are actually in the gut, and they are not very persistent.

That means that in a field of lambs, there will three different groups:

How many of each type of lamb you have at any moment is difficult to say. It’s a good idea to take faecal samples to assess parasite burdens.

However, in practice, treatment is often based on suspicion. This probably means some lambs are treated that don’t need treating. However, this is generally seen as an acceptable compromise for the greater good.

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