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International audience; Strongyle infection is an important issue in horse breeding. It impairs horse health and performance, with young horses being the most sensitive. Strongyle control has long relied on the systematic use of chemical treatments. However, expanding anthelmintic resistance among strongyles calls for alternative options. Mixed grazing is assumed to reduce strongyle load on the pasture as the result of a dilution effect. This has been shown in small ruminants grazing with cattle, but the putative benefits of co-grazing between horses and cattle have not yet been evaluated. Here, we conducted field surveys and face-to-face interviews on 44 farms from two contrasted saddle-horse production areas, Normandy and northern Massif Central, to compare equine strongyle management practices between specialized systems and mixed horse-cattle systems. Our goals were (i) to quantify breeders' awareness of the putative benefits associated with the co-grazing of horses and cattle, (ii) to establish whether mixed farming was associated with different strongyle management strategies and (iii) to test whether strongyle egg excretion was reduced in horses grazed with beef cattle. Every breeder relied on systematic calendar treatments, and only 8 out of the 23 mixed breeders were aware that co-grazing of horses with cattle could be used as part of their strongyle control strategy. Management practices were similar across both systems in Normandy. In Massif Central, mixed breeders formed a distinct cluster from their specialized counterparts: deworming was less frequent and stocking density was higher in mixed farms, while specialized breeders seemed more willing to integrate herd and plot management into control strategies. Faecal egg counts measured in horses from Massif Central were significantly reduced when horses were grazed with cattle. This was the result of an increased reliance on macrocyclic lactones in mixed farms (P < 0.01) and a significant dilution effect (P < 0.01). When considering a subsample of horses treated with macrocyclic lactones only, young horses grazed with cattle had 50% fewer strongyle eggs excreted in their faeces than horses grazed in equine-only pastures (P < 0.01). This is the first evidence of the benefits of mixed grazing with cattle as an alternative to control strongyle infection in horses, although this promising alternative remains largely unknown by horse breeders.

Les parties prenantes ont besoin d'outils opérationnels pour évaluer les stratégies de protection des cultures en ce qui concerne l'impact environnemental. La nécessité d'évaluer et de rendre compte des impacts de l' utilisation des pesticides sur l'environnement a conduit à l'élaboration de nombreux indicateurs . Cependant, seulement un peu d' études ont porté sur la prédiction qualité de ces indicateurs . Cela est principalement dû au nombre limité d' ensembles de données adaptés à la comparaison des résultats des indicateurs avec la mesure des pesticides . À notre connaissance, l' évaluation de la prédiction qualité de Les indicateurs de pesticides comparés à la qualité de l' eau présentés dans cet article sont sans précédent en termes de nombre d' indicateurs testés ( 26 indicateurs et le modèle MACRO ) et en termes de taille des ensembles de données utilisés (données collectées pour 4 voies de transfert, 20 ingrédients actifs ( a .i.) pour un total de 1040 points de comparaison). Résultats obtenus sur un.je. les mesures ont été comparées aux résultats des indicateurs, mesurés par: (i) tests de corrélation pour identifier les relations linéaires, (ii) tests de probabilité comparant les mesures avec les résultats des indicateurs, classés en 5 classes, et évaluant la probabilité d' estimation et de surestimation (iii) par des tests ROC estimant la capacité prédictive par rapport à un seuil donné. Les résultats ont montré que la corrélation entre les sorties d'indicateurs et les transferts observés est faible (r, Stakeholders need operational tools to assess crop protection strategies in regard to environmental impact. The need to assess and report on the impacts of pesticide use on the environment has led to the development of numerous indicators. However, only a few studies have addressed the predictive quality of these indicators. This is mainly due to the limited number of datasets adapted to the comparison of indicator outputs with pesticide measurement. To our knowledge, evaluation of the predictive quality of pesticide indicators in comparison to the quality of water as presented in this article is unprecedented in terms of the number of tested indicators (26 indicators and the MACRO model) and in terms of the size of datasets used (data collected for 4 transfer pathways, 20 active ingredients (a.i.) for a total of 1040 comparison points). Results obtained on a.i. measurements were compared to the indicator outputs, measured by: (i) correlation tests to identify linear relationship, (ii) probability tests comparing measurements with indicator outputs, both classified in 5 classes, and assessing the probability i.e. the percentage of correct estimation and overestimation (iii) by ROC tests estimating the predictive ability against a given threshold. Results showed that the correlation between indicator outputs and the observed transfers are low (r < 0.58). Overall, more complex indicators taking into account the soil, the climatic and the environmental aspects yielded comparatively better results. The numerical simulation model MACRO showed much better results than those for indicators. These results will be used to help stakeholders to appropriately select their indicators, and will provide them with advice for possible use and limits in the interpretation of indicator outputs.