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Nematodirus and coccidia in young lambs

Nematodirus and coccidia in young lambs

The first two parasite challenges young lambs will face each spring is that of nematodirus and coccidia. This challenge occurs in lambs annually at a similar age and stage of the year, Ciaran Lynch, Teagasc Sheep Specialist, explains more.

It’s also possible for lambs to suffer from a concurrent infection with both parasites at the same time. When dealing with either of these parasites prompt treatment is necessary, as they can have immediate and long lasting effects that damage the gut. This effects the lamb’s ability to adsorb nutrients and, in severe cases, they can cause mortality. In both cases, treatment should be based on clinical signs, timing and farm history. Reliance on faecal sampling is not recommended for these parasites in young lambs.


Coccidia are a tiny single celled (protozoa) parasite which affects young lambs. There are a number of different species in the environment, however only two of these are pathogenic to sheep. Coccidia can survive on pasture and in the environment (around water trough/drinkers etc.) from the previous grazing season. Although the vast majority of sheep farms will have coccidia, not all farms will have to treat for it as it can be a farm specific issue - previous farm history is important. The parasite needs wet conditions to become active. The level of burden on the farm can vary in a given year, thus influencing the challenge lambs face.

 In general, coccidia primarily effects lambs from 2 weeks up to 8–9 weeks of age. Although it can occur in older lambs, where immunity is supressed or where naïve lambs face a heavy burden. The coccidia oocysts are ingested via the mouth and then travels to the gut where it enters the gut wall. From there it will then burst out causing damage in the process. As a result lambs present with diarrhoea often containing mucus or blood; they may also show signs of straining and appear empty/dehydrated. The capacity of the gut to absorb nutrients is compromised and in some cases won’t regenerate resulting in pining lambs, which is one of the long term negative side effects of this parasite – in more severe cases it can cause death.

As it takes 2 to 3 weeks from infection until the coccidia oocysts are passed out in the faeces, diagnosis based on faecal egg sampling is not a useful measure in this case. That combined with the fact the result may be an indication of non-pathogenic as opposed to pathogenic species – a point worth remembering later in the season when interpreting results of faecal egg tests. Diagnosis should be based on previous farm history and age of lambs with prompt treatment at the first sign of the condition on farms with a known issue.

There are a number of treatment options available that are outlined below. Discuss these with your vet to determine the most appropriate for your farm. In all cases, the first aim needs to focus on reducing the environmental burden. Keeping areas around drinkers and feeders clean, dry and hygienic helps reduce the burden in the environment. When outdoors, regularly moving feeders - particularly where poaching is occurring - will also help. Ideally keeping different ages of lambs separate at turnout i.e. later lambs grazing a different area initially than older lambs, but this has practical limitations.

Treatment is based on the use of oral drenches with an in feed medication also available. The drenches are based on two different ingredients either Diclazuril or Toltrazuril and the in-feed medication is based on using Decoquinate

  • Diclazuril based products interrupts the life cycle of the coccidia for two weeks. Consequently, when using this product, a repeat treatment may be needed 2-3 weeks after the initial treatment. These products have a short withdrawal period.
  • Toltrazuril based products are active against all development stages of coccidia. It lasts longer in the lambs system, consequently one treatment is usually sufficient. However, these products tend to have a longer withdrawal period.
  • Decoquinate can be included in the feed with a number of mills having the licence to do this. The level of inclusion will vary depending on the expected feed intake. It is recommended that the inclusion rate in feed is contain 100mg decoquinate/kg feed.  Lambs need to consume 100g of creep feed per 10kg live weight for a period of 28 days.


Nematodirus (battus) is the other main parasite which is pathogenic to young lambs. In general, nematodirus affects lambs aged from 6 to 12 weeks. However, it may occur in younger lambs particularly those where milk supply is compromised for other reasons e.g. twins or triplets on poor mothers. Following exposure, lambs develop varying levels of immunity to this parasite.  

The nematodirus eggs overwinter on pasture from the previous grazing season. These eggs hatch on pasture when they are exposed to a cold period followed by an increase in temperatures above 10ºC. When the hatch occurs, there is vast number of these infected larvae on the pasture. This typically occurs in April to May depending on location and prevailing conditions. This hatch also coincides with the stage of the year where young lambs start consuming larger quantities of grass. The mass hatch poses a high level of challenge for young naïve lambs; once ingested the nematodirus larvae damage the lining of the intestine resulting in diarrhoea, dehydration, weight loss and - if left unchecked - can also result death.

As the damage is caused by the larvae that are not producing eggs, it means faecal egg counts are not a useful form of diagnosis. Each year, the Department of Agriculture issues a nematodirus warning, developed in in collaboration with Met Éireann, UCD and Teagasc, that indicates when the peak hatch occurs around the country. Use this information in combination of visual signs and risk assessment on each farm to determine the best time to treat this parasite. The 2023 Nematodirus forecast can be found here

Treatment is based on using anthelmintic drenches. There is currently no known case of resistance detected to any of the anthelmintic classes for nematodirus in Ireland. However, in order to preserve the efficacy of these other classes for later in the season, it is recommended that lambs should only be treated with a Benzimidazole (1-BZ – white drench) based product. This is one of the key actions to improve sustainability. Read more here. Remember, no product offers residual activity against nematodirus, so a second treatment may be necessary as lambs may become re-infected particularly for those running mixed age grazing groups. 

Take care when dosing

Given that this is the first dose many young lambs will receive, it ss important care is taken when administering the dose. This can be problematic as young lambs can be sometimes more awkward to restrain than older lambs. Unfortunately each year some lambs are lost as a result severe pharyngeal injury caused by the dosing gun. Not all of these injuries are immediately obvious, the injury may cause pockets that become a reservoir for feed particles that can become a source for subsequent infections. As with all times when administering anthelminthic, it’s essential to ensure the dosing equipment is calibrated correctly and consistently delivering the recommended amount.