It is a general believe that the local sheep breed Churra da Terra Quente (CTQ), reared in the Northeast of Portugal is well adapted to the conditions of its production system. However, there are large gaps on our knowledge to allow understanding of such claimed adaptation. Several researchers have found differences in digestibility between sheep breeds (e.g. Givens and Moss, 1994; López et al., 2001), suggesting that those fed natural resources can have an improved ability to digest fibre. This experiment was designed to compare digestibility coefficients of a high– and a low–roughage diet measured on sheep from CTQ and Ile-de-France (IF) breeds at the same degree of maturity.