RT Journal Article SR Electronic T1 Risk factor analysis of equine strongyle resistance to anthelmintics JF bioRxiv FD Cold Spring Harbor Laboratory SP 158105 DO 10.1101/158105 A1 G. Sallé A1 J. Cortet A1 I. Bois A1 C. Dubè A1 Q. Guyot-Sionest A1 C. Larrieu A1 V. Landrin A1 G. Majorel A1 S. Wittreck A1 E. Woringer A1 A. Couroucé-Malblanc A1 J. Guillot A1 P. Jacquiet A1 F. Guégnard A1 A. Blanchard A1 A. Leblond YR 2017 UL http://biorxiv.org/content/early/2017/07/03/158105.abstract AB Digestive strongyles are the most problematic endoparasites of equids as a result of their wide distribution and the spread of resistant isolates throughout the world. While abundant literature can be found on the extent of anthelmintic resistance across continents, empirical knowledge about associated risk factors is missing. This study brings together results from anthelmintic efficacy testing and risk factor analysis to provide evidence-based guidelines in the field. It involves 688 horses from 39 French horse farms and riding schools to both estimate egg reduction rate (ERR) after anthelmintic treatment and to interview premise managers about their practices. Risk factors associated with reduced anthelmintic efficacy in equine strongyles have been estimated across drugs or for every drug class separately using a marginal modelling approach. Results demonstrate ivermectin efficacy (96.3% ERR), the inefficacy of fenbendazole (42.8% ERR) and an intermediate profile for pyrantel (90.3% ERR). Risk factor analysis provide robust support to advocate for FEC-based treatment regimens as well as individual determination of anthelmintic dose that contribute to significantly lower drug resistance risk by factors 1.72 and 2.56 respectively. In addition, reduced horse movements should also be recommended to sustain anthelmintic efficacy (odd ratio=0.42 [0.26;0.69]) while the horse-to-worker ratio may be an indicator of better efficacy. On the contrary, outdoor-breeding systems, grazing systems with little rotation and manure spreading significantly increased the risk of reduced drug efficacy by factors 1.71 to 7.56. This is the first empirical risk factor analysis for anthelmintic resistance in equids, whose findings should guide the implementation of more sustained strongyle management in the field.