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International audience; Bovine dictyocaulosis is a pulmonary disease caused by the presence and development of the strongyle Dictyocaulus viviparus in the trachea and bronchi of cattle. This parasite is mostly observed in temperate countries, with potential important clinical and economical impacts. Individuals that already had contact with the parasite normally develop a strong acquired immunity. However, when the first contact with the parasite was poor and the contamination of the environment is high, clinical signs can occur. In such a context of clinical dictyocaulosis outbreak in dairy herds, current recommendations are to treat the whole herd with anthelmintic because of the presence of subclinical infestations. However, current guidelines against anthelminthic resistance recommend the use of selective treatment on adult cattle in order to maintain a refuge helminth population unexposed to anthelmintic. According to the heterogeneity of acquired immunity in a herd, and hence, of sensitivity of animals to parasitic infestation by D. viviparus, an early targeted selective treatment of clinically affected and main shedders animals may be effective to control the disease in the herd. Such a strategy was never tested for dictyocaulosis and a field validation is thus necessary to ensure a proper control of ditycocaulosis at the herd level.ObjectivesThis study is a pilot study designed to assess the clinical relevance of a targeted selected treatment against D. viviparus at the beginning of a dictyocaulosis outbreak in dairy herds.Materials and methods. In each herd with clinical signs of dictyocaulosis, we performed broncho-alveolar lavage on 6 cows and a pooled McKenna sedimentation on 10 cows of the herd to test for the presence of D. viviparous. We implemented a targeted selective treatment in three positive dairy herds by treating with injectable eprinomectine approximately 50% of the dairy cows including clinically affected, primiparous and postpartum cows. The follow-up was implemented one and three months after the targeted selected treatment by performing broncho-alveolar lavage and a pooled McKenna sedimentation. The farmers recorded clinical signs of dictyocaulosis at the herd level during the whole study period.ResultsIn the three followed dairy herds, symptoms of dictyocaulosis vanished after the targeted selective treatment. After the treatment, we assessed a dictyocaulosis incidence rate of 2% by month during the whole follow-up, which indicates a low but persistent circulation of the parasite in the herd. Clinical signs of dictyocaulosis, remained very low to inexistent in the three herds during the whole study period. ConclusionThe targeted selective treatment implemented in the three herds of this study was efficient to control dictyocaulosis at the herd levels. To our knowledge, this study is the first to prove the potential interest of a targeted selective treatment to control dictyocaulosis at the herd level. These results should be confirmed in a larger study with more herds.