Leptin is a 16kDa peptide hormone mainly secreted by fat cells to regulate of food intake and energy homeostasis, and to signal the status of body energy stores to the brain (Houseknecht et al., 1998). In ruminant, reducing feedstuffs particle size increases DM intake, particularly if feedstuffs quality is poor, due to a shorter retention time of the particles in the rumen. By-products are included in the ration to supply energy and protein, but they have often a high content of fibre. The by-product fibre has different properties than forage NDF, being characterised by particles of small dimensions and a high density. The aim of this study was to compare the plasma level of leptin in lactating goats fed a traditional silage-based diet or a totally free forage diet, throughout lactation and during the pre and post-feeding state.