Résumé
The collective economic and environmental interest of the whole dairy sheep sector is to reduce feedcosts and the negative impact of milk production on the environment. Thus, this study focused on thecharacterisation and genetic selection potential of feed efficiency in the Lacaune breed. Estimates for feedefficiency in dairy ewes are limited, mainly due to a lack of individual feed intake measurements in thesheepfold or in the pasture. We estimated the genetic parameters for two approximated (not entirelybased on individual data) feed efficiency traits (lactation feed conversion ratio (LFCR) and residual energyintake (REI)) and daily milk yield (DMY) at different stages of lactation and throughout lactation. Theaccuracy of the efficiency traits was first evaluated on samples from Lacaune dairy ewes that were mon-itored individually, especially for their feed intake. Then, feed efficiency estimation methods were appliedon eight commercial farms corresponding to 4 680 Lacaune dairy ewes over two milk lactations (30 854records). Animals were collectively (for a large part of feed intake) or individually (for milk performanceand dynamics of body fat reserves) monitored at different lactation stages. The heritabilities of LFCR andREI were estimated over lactations at 0.10 ± 0.01 and 0.11 ± 0.01, respectively. High genetic correlationswere observed between the two efficiency traits and milk production traits, with a genetic correlationbetween LFCR and DMY of 0.74 ± 0.04 and between REI and DMY of 0.79 ± 0.04. A strong influenceof environmental factors such as farm, year of milk production and lactation stage affected the geneticlink between REI and milk production traits. Efficiency values observed in early lactation when animalswere bred in the sheepfold were less genetically correlated with values obtained later in lactation whenanimals were grass-fed. However, individual characterisation of feed efficiency remains difficult due tothe collective feeding context in dairy ewe farms.