Modifications of maternal environment could alter fetal growth and development through the placenta and thus health in adulthood. Osteochondrosis is an osteo-articular pathology which affects young horses and strongly impacts the equine industry. It has been shown that breeding practices, especially feeding pregnant mares with concentrate in the last part of gestation, could play a role in the development of this disease . To understand the effect of feeding practices during gestation, 24 saddlebred mares were allocated to one of two groups: group B was supplemented twice a day with barley (B) and group F was led only with fodder (F) between the 7th month of gestation and foaling. B mares maintained an optimal body condition score through gestation, with an increase in glycaemia and insulinemia alter each meal and an insulin resistance in the 9th month of gestation. F mares lost condition as assessed by body condition score in the last part of gestation, leading to a moderate undernutrition and a transitional increase in Non Esterified Fatty Acid plasma concentrations. Diets had no effect on feto-placental biometry, nor on placental structure. ln contrast, an increase in microcotyledonary vessel volume was observed in F placentas, indicating placental adaptation, possibly to increase fetomaternal exchanges- There was no overall difference in the expression of genes involved in vascularization, nutrient transfer growth and development between placentas from B and F mares. Nevertheless, as seen by others , sex-specific effects of maternal nutrition were observed in placentas from female foals, with differences in the expression of Endogline, Kinase insert Domain Receptor, lnsulin-like Growth Factor 2 and lnsulin-like Growth Factor 1 Receptor genes. This study demonstrates that breeding practices, i.e., supplementation in concentrate at mid-gestation, do not seem to affect fetal development.