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Coccidiosis and nematodirosis in young lambs

Coccidiosis and nematodirosis in young lambs

At this time of year, the major parasites of concern for young lambs are Nematodirus and Coccidia. Coccidiosis is a disease of young lambs, usually from 3-8 weeks of age.The signs of nematodirosis are similar to coccidiosis. Orla Keane, Teagasc Researcher explains both parasites & their effects.


Coccidia are protozoan parasites of the genus Eimeria.  There are many different Eimeria species that can infect sheep but only two cause disease; therefore, faecal egg counts are not necessarily a good indicator of infection, as they cannot distinguish between the species. Coccidiosis is a disease of young lambs, usually from 3-8 weeks of age. New-born lambs have passive immunity transferred in colostrum. Lambs become susceptible at 2-3 weeks of age and remain susceptible until immunity develops at approximately 8 weeks of age.

Coccidiosis symptoms

Coccidiosis can result in profuse diarrhoea that can be dark or even blood stained, with straining and weight loss. If left untreated the disease can be fatal.  Even if treated, severe disease may result in damage to the gut, which prevents the lamb from thriving. The parasite is transmitted by the faecal-oral route, and coccidia oocysts require moisture to become infective. Older lambs can shed large numbers of oocysts into the environment even after they develop immunity and can be a significant source of contamination for younger lambs in the flock.

Prevention & Control

Control of coccidia relies on lowering the number of oocysts that lambs are exposed to and appropriate preventative treatment where necessary. Reducing environmental contamination indoors requires preventing over-crowding, providing clean bedding and keeping areas dry. Outdoors, preventing faecal contamination of feeders and troughs and keeping the area around them dry helps prevent the spread of infection. Keeping younger lambs off ground previously grazed by older lambs will also reduce their exposure to the parasite.


Treatment can be in-feed or more commonly by drenching with products containing either diclazuril or toltrazuril. The timing of treatment is important and lambs should be treated 1-2 weeks before expected disease. Lambs treated with diclazuril may require repeat treatment approximately 3 weeks after the first treatment as this drug has no residual activity.


Nematodirus battus is a gastrointestinal nematode that can also cause disease in young lambs. The lifecycle of Nematodirus is unlike other gastrointestinal nematodes in that the larvae develop within the egg and chilling followed by warmer temperatures are required for larvae to hatch from the egg.  Therefore, there can be a synchronised mass hatching of Nematodirus in spring, when conditions are favourable. If this mass hatch coincides with susceptible young lambs grazing sufficient quantities of grass (usually lambs 6 weeks and older) then disease can strike rapidly. Lambs consuming more grass, such as twin lambs or lambs of ewes of poor milking ability may be more susceptible to disease. Lambs will generally develop immunity by approximately 12 weeks of age.

Signs of nematodirosis

The signs of nematodirosis are similar to coccidiosis with profuse diarrhoea, weight loss and in severe cases death. The severity of disease, if lambs are affected by both parasites, will be greater. The Department of Agriculture, Food and the Marine, in collaboration with Met Éireann produce a Nematodirus forecast that predicts when peak Nematodirus hatching will occur around the country.


At risk lambs should be treated 2 weeks after the predicted hatch. Treatment for Nematodirus involves drenching with a product from the benzimidazole class of anthelmintics (white drenches). No anthelmintic product has residual activity against Nematodirus and so repeat treatment may be required 2 to 3 weeks after initial treatment, particularly if there is a wide age range in a group of lambs.  Faecal egg counts are not a good indicator of when to treat for Nematodirus as the larval stage of the parasite damages the gut, therefore damage may be done before eggs appear in the faeces.  

Dr Orla Keane joined Ciarán Lynch on a recent episode of OviCast to discuss Nematodirus in lambs. Listen in below

Find out more about Nematodirus & Coccidiosis here or watch a recent episode of the Let's Talk Sheep webinar series here