Selection of feeding sites by horses at pasture: Testing the anti-parasite theory Geraldine Fleurance a, * , Patrick Duncan b , Herve Fritz b , Jacques Cabaret c , Jacques Cortet c , Iain J. Gordon d,1 a Les Haras Nationaux, Direction des Connaissances, Station Expe ´rimentale des Haras Nationaux, 19370 Chamberet, France b Centre d’Etudes Biologiques de Chize ´, CNRS UPR 1934, 79360 Beauvoir-sur-Niort, France c INRA, Infectiologie Animale et Sante ´ Publique, 37380 Nouzilly, France d The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom Accepted 19 November 2006 Available online 15 December 2006 Abstract Management of grazed grasslands for production and/or conservation objectives requires a thorough understanding of the choices of feeding sites by herbivores, and of the biological processes involved. Most models of the feeding strategies of herbivores are based on the principle that optimising the intake of energy (or some nutrient) is the primary goal of foragers but other selective forces, such as parasitism, could be important. Gastrointestinal parasites (including cyathostome nematodes) have powerful effects on the fitness of herbivores and may act as a major selection pressure favouring host behaviour that reduces the risk of encountering parasites. Among large herbivores, horses have perhaps the most marked tendency to select particular feeding sites within grasslands. We test here: (1) whether horses select feeding patches with relatively low parasite densities and (2) if their choice is affected by their parasite load. We used 10 two-year old saddle-horses and three periods. In the first period, the horses were under natural parasitism which varied strongly among individuals; in the second period they were all dewormed, and in the third, a sub-set of the horses was experimentally infected with cyathostome larvae. Ninety-eight percent of the infective larvae in the pasture were found <1 m from faeces. The main determinant of the choice of feeding patch by horses was the availability of patches of different parasite risk and grass height. Controlling for availability, the horses used tall grasses (>16 cm) less than expected, whether the grass was contaminated or not, and they selected for short patches >1 m from faeces, where the risk of encountering parasites was low. These results suggest that selection of feeding sites by horses is driven by an interaction between their www.elsevier.com/locate/applanim Applied Animal Behaviour Science 108 (2007) 288–301 * Corresponding author. Present address: INRA Clermont-Ferrand/Theix, Unite ´ de Recherche sur les Herbivores, 63122 Saint-Gene `s-Champanelle, France. Tel.: +33 473 62 4652; fax: +33 473 62 4118. E-mail address: geraldine.fleurance@clermont.inra.fr (G. Fleurance). 1 Present address: CSIRO, Davies Laboratory, PMB PO Aitkenvale, Qld 4814, Australia. 0168-1591/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2006.11.019