The optimum dietary requirements for macrominerals (calcium and phosphorus) and trace elements (zinc and copper) in mares and foals of horse breeds characterized by rapid growth is still unknown. However, published recommendations are known to prevent deficiencies. This article presents the results of a three-year survey (1997-99) on the diet composition of mares and foals from 14 farms in Normandy, France. The survey was conducted to determine the influence of the diet on developmental orthopaedic disease (DOD). The feed compositional data obtained showed that low levels of copper and zinc are common in pasture and roughage sources. The data also reflect wide variations in mineral content of supplements and complementary feeds.