Managing infections of sheep with anthelmintic resistant gastrointestinal nematodes (Gin) is a major challenge for sheep producers in Western europe. new methods of grazing management have been poorly explored as a component of an integrated and sustainable control of these parasites. therefore, the purpose of this study was to evaluate the effect of two different types of grazing systems of sheep (intensive cell grazing versus conventional rotational grazing) on Gin infections over two years in a farm located in a temperate environment of Western france. When considering the whole study, the type of grazing system did not influence significantly the intensity of egg excretions of adult ewes even if the proportion of ewes excreting high numbers of Gin eggs was higher in cell grazing system than in rotational grazing system. The most striking result of this survey was the effect of grazing system on the Gin species composition harbored by ewes and by their lambs: with time, the proportions of H. contortus infections were lower in cell grazing system than in rotational grazing system. in conclusion, the cell grazing system, as implemented in this study, could limit the importance of this highly pathogenic nematode species in sheep.

Gastrointestinal nematode (GIN) infection is one of the major health issues in sheep worldwide. In temperate countries of Western Europe, three GIN species dominate the digestive helminthofauna of sheep: Teladorsagia circumcincta, Haemonchus contortus and Trichostrongylus colubriformis. All of them are responsible for growth retardation and milk production losses 1 ; however, only H. contortus infections can lead to high mortality rates in lambs and ewes, especially when climatic conditions are optimal for the development of free-living stages on pastures and when sheep are exposed to them at grazing. For decades, the control of GIN relied exclusively on anthelmintic treatments. However, the effectiveness of anthelmintics, and the welfare and production benefits they bring, is threatened by the increasing prevalence and severity of anthelmintic resistance. Western Europe is more and more facing multiple-resistance in GIN 2-4 . In Southwestern France, the first ivermectin and benzimidazoles resistant Haemonchus contortus isolate has been reported recently 5 . In this context, control strategies for GIN that minimize the use of anthelmintics are of increasing importance not only in organic farms but also in conventional farms. Many components of an integrated control program have been investigated such as selection of a genetic resistance in sheep 6 , vaccination against H. contortus infection 7 or the use of condensed tannins in alimentation 8 . Some other strategies are focusing on the limitation of pastures contamination by using nematofagous fungi 9 . In comparison, the effects of pastures management on GIN infections in sheep have received less attention with the notable exception of mixed or alternate sheep and cattle grazing 10 or studies performed in Australia (Cicerone project in New South Wales), where the effects of cell grazing system on GIN infections were evaluated in comparison with a typical rotational grazing system 11,12 . Cell grazing system is characterized by the division of pastures in many small "cells" (less than 0.5 hectares (ha)) in which sheep or cattle are allowed to graze for a very short time (usually less than two days) at a very high instant stocking rate (about 500 sheep per hectare). This is strictly different from typical rotational grazing system where grazing periods are longer (one