Internal parasites cause major production and financial losses for sheep farmers. In the case of young lambs, two such parasites – nematodirus and coccidia – are of particular concern.

If left unchecked, these can cause major losses in terms of lamb mortality and lack of thrive in infected lambs that survive.

Nematodirus

Nematodirus battus can cause a problem for lambs from four to 12 weeks old. The main risk factors of concern are as follows:

  • Lambs grazing pasture that was grazed by lambs or young calves the previous spring.
  • Lambs old enough to be eating a significant amount of grass and, therefore, facing an increased risk of ingesting large numbers of worm larvae.
  • Twin lambs, because they start grazing earlier will be under threat at a slightly younger age.
  • A cold period (typical of March or April) followed by warm weather, which triggers the synchronised hatching of eggs which are on the pasture since the previous spring.
  • Larvae ingested, often in large volumes, attack the lining of the gut causing much damage in a short time.

    • Therefore, lambs over five weeks old in April and May are most at risk. However, the disease can occur at other times. It is important to note that while larvae cause a lot of damage, it is only adult worms that produce eggs. Therefore, faecal egg counts are of little use in determining if there is a need to treat lambs.

    Due to the effect of prevailing weather conditions, the Department of Agriculture, Food and the Marine (DAFM) regularly issues warnings, usually in April or May, when they predict a likely outbreak of the disease. These warnings should be treated seriously.

    Symptoms

    Lambs may be seen with the head down, drooped ears, possibly with the abdomen tucked up due to pain. Lambs will typically develop a scour and, if allowed to develop, the infection can lead to profuse diarrhoea and wasting. However, as the lambs may stop eating, the scour may only consist of slimy mucus.

    Due to dehydration, lambs will be thirsty and may congregate around a watering trough. Mortality can be high in untreated lambs.

    Prevention and control

    The infection is best prevented by keeping the current year’s lambs off grassland that was grazed by lambs the previous year.

    This could be on ground that was closed from early spring until after first-cut silage, or grazed with adult cattle (excluding calves) in the previous year. In the absence of clean pasture, a dose is desirable. In the case of nematodirus, there is no evidence of anthelmintic resistance to any of the drug classes on the market.

    Furthermore, the manufacturers of macrocyclic lactones (injectable or clear drench) generally do not claim any residual activity against nematodirus. Therefore, a white or yellow drench (benzimidazole or levamisole) are the doses of choice.

    The information presented in Table 1 outlines the identifying symptoms and prevention/control measures recommended for nematodirus and coccidiosis.

    Coccidiosis

    Coccidiosis is not caused by a roundworm, rather by a small parasite called Eimeria, which is not visible to the naked eye.

    While there are many different species of coccidia, only two are considered pathogenic, namely Eimeria ovinoidalis and Eimeria crandalis.

    All sheep carry a small number of coccidia in their gut and these do not cause any disease symptoms. Lambs become infected orally from faecal contamination of bedding, water troughs or feed troughs.

    The principal source of infection for young lambs is contamination of the environment by lambs born earlier in the season. Bedding, drinkers and feeders where lambs congregate will contain large numbers of oocysts (coccidial eggs).

    Very young lambs, younger than two weeks old, are not affected due to the immune protection received via the colostrum. The greatest risk period for lambs is between three and eight weeks of age, with clinical symptoms most apparent from six to eight weeks of age. Once exposed, lambs develop a solid resistance to coccidia and lambs over 10 weeks tend to be resistant.

    Symptoms

    A severe scour which may contain blood or is black in colour is common. Affected lambs will strain and, if untreated, mortality can be high. Lambs that are badly affected but subsequently survive will have irreversible damage done to their digestive tract and will thrive poorly. Stress, poor nutrition and simultaneous infection with nematodirus can increase the severity of infection. If lambs start to scour or continue to scour within a few days after dosing for nematodirus, coccidiosis is likely to be a problem.

    Prevention

    Coccidiosis is best prevented by keeping the level of challenge low. The parasite needs water to hatch into the infected stages. Therefore, avoiding overcrowding (indoors) and maintaining clean and dry bedding is useful in reducing exposure.

    Avoid faecal contamination of feed area and drinking troughs, and keep these at a raised level. These troughs should be moved frequently to a clean area during the risk period of three to 10 weeks. Where possible, young lambs should be kept in groups within a two-week age range. They should not be mixed with older lambs until they are at least eight weeks old and should not graze pasture where older lambs have been.

    In the case of a history of coccidiosis on a farm, a preventative treatment can be used. Incorporating a feed additive for lambs being creep-fed concentrates is an option. The additive Deccox (Forum Products Ltd) is available as a prescription-only medicine. It may only be incorporated by feed millers that have a special licence to incorporate medicines into concentrate feeds.

    Control

    Treatment should be undertaken after consultation with your veterinary surgeon. Oral drenches that have residual activity varying from two to eight weeks are available.

  • Vecoxan (Jannsen Animal Health): Two-week residual activity; withdrawal period of zero days.
  • Baycox Sheep (Bayer): Two-week residual activity; withdrawal period of 42 days.

    • Lambs badly affected with coccidiosis should receive additional supportive antimicrobial therapy (sulphonamide powders or injections).

    Nematodirus and coccidiosis are of concern for young lambs. If left unchecked, they can cause high levels of lamb mortality and poor thrive in lambs.

    Treatment for nematodirus should be given at the first sign of scouring once lambs are eating grass. With the aid of the DAFM forecast, consider treating before scouring begins. By the time lambs start to scour, there is already some damage done to lining of the gut. White or yellow drenches are the doses of choice for nematodirus.

    Treatment options should be discussed with your veterinary surgeon.

    Frank Hynes is a Teagasc sheep specialist at the Animal and Grassland Research & Innovation Centre, Teagasc, Athenry, Co Galway.