-The use of anthelmintics is strongly limited in organic farming. This may induce a change in the intensity (no of worms) and diversity (proportions of species) of helminth infection. Helminths remain a major preoccupation in organic sheep farming: high levels of infection have been recorded on several farms and helminth diversity is always higher. The helminth infection in milk cattle of northern Europe is controlled and diversity is higher in organic farms, as recorded in sheep. The role of helminth diversity on intensity is still unclear. Grazing management is one of the means to controlling helminths. The use of safe pastures for calves and sheep after weaning is one of the major components of control. The use of alternate or mixed grazing is common for cattle in northern countries but is uncommon for sheep in France. Grazing management is not sufficient to controlling infection in sheep and conventional anthelmintic treatments are performed. Additionally, alternative treatments are used. The alternative therapies based on phytotherapy or homeopathy are largely recommended in organic farming but do not have any demonstrated efficacy. More research is needed to evaluate such therapies. ruminant organic farm / helminth / grazing management / anthelmintic / phytotherapyRésumé -Gestion des helminthes de ruminants en agriculture biologique. L'emploi des anthelminthiques est fortement limité en élevage biologique. Cette diminution de leur utilisation peut conduire à des changements en ce qui concerne l'intensité (nombre de vers) et la diversité (proportion des espèces) des parasites. Les helminthes sont une préoccupation majeure en élevage biologique ovin : les infestations sont très fortes dans certaines fermes et la diversité est plus élevée que dans les élevages conventionnels. L'infestation des bovins laitiers par les helminthes dans les pays du nord de l'Europe est assez bien contrôlée et la diversité est plus forte également en élevage biologique. Le rôle de la diversité sur l'intensité n'est pas encore clair. La gestion des pâturages est l'un des moyens de contrôler l'infestation. L'utilisation de pâtures saines pour les veaux ou les agneaux après le sevrage est l'une des composantes essentielles de la gestion des parasites. L'utilisation de pâturage alterné ou mixte avec des espèces différentes est commun dans les régions nordiques pour les bovins mais n'est 625

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Organic meat sheep producers are limited by their access to and permitted use of synthetic drugs to effectively control internal parasites, and they are limited further still, by the narrow array of efficient alternative drugs available to them. The use of targeted selective treatments, for the control of parasites, e.g. treating only the lambs that cannot cope with infection, would be of interest. The difficulty is in identifying those specific lambs in need of treatment. FAMACHA © (an anaemia indicator) has been used with success in tropical areas where the blood sucking worm Haemonchus contortus is the main gastrointestinal nematode. From their own experience, farmers may also be able to detect lambs in poor, average or good condition, possibly relative to parasite infection burden, a method referred to as farmers' eye score. Using the farmers'eye score to judge lambs in need of treatment was not found to be fully efficient. It was however, significantly related to the presence of Moniezia eggs and to the number of Trichuris and possibly Nematodirus eggs in faeces but remained unrelated to the excretion of other gastrointestinal nematode eggs. The farmers'eye score was in agreement with the average faecal egg counts but the accuracy of individual detection of lambs in need of treatment, remained low (49% correctly classified). The FAMACHA © had an even lower efficiency to detect lambs requiring treatment. The farmers'eye score when correcting for farm variability was improved and highly correlated to the infection with Nematodirus. The farmers'eye score should be improved using pathophysiological indicators (diarrhoea score, weight gains..) or/and by harmonisation among farmers, if it is to be relied upon to detect animals in need of anthelmintic treatment in the future.