Abstract In equids, maternal size affects fetal intrauterine development [Allen WR, et al; Reproduction 2002;123:445-53] and insulin sensitivity in the neonatal period [Forhead AJ et al; J. Endocrinol. 2004;181:459-67], but long-term effects have not been described. We enhanced or restricted fetal growth through embryo transfer using Pony (P), Saddlebred (S) and Draft (D) horses to investigate long term glucose metabolism. Control pregnancies of P-P (n=21) and S-S (n=28) were obtained by artificial insemination. Enhanced and restricted pregnancies were obtained by transferring P (P-D, n=6) and S embryos (S-D, n=8) into D mares or S embryos into P mares (S-P, n=6). From birth to weaning (180 days), control and experimental foals were raised by their dams and recipient mothers, respectively. Foals were muzzled and fasted 4 hours at age 3 days, 6 hours at age 4 months and overnight from age 6 months and maintained with their dam before sampling for glucose metabolism. Fasting glycemia was recorded at regular intervals from 3 days to 18 months of age. At age 3 days, 4 months (pre-weaning) and 1 year (post-weaning), glucose clearance and insulin secretion were assessed with intravenous glucose tolerance tests (IVGTT). On days 200 (early post-weaning) and 18 months, insulin sensitivity was measured with hyperinsulinemic euglycemic clamps. Statistical analysis was performed by Kruskal-Wallis with Dunn's posthoc test. P-P had higher fasting glycemia from 1 month to 18 months of age, with reduced insulin sensitivity compared to S-S confirmed by all dynamic tests (p<0.05). “Enhanced” P-D had higher insulin secretion than P-P after IVGTT on day 3 (p<0.05) and lower fasting glucose from 1 month to 18 months of age (p<0.05). Clamps and IVGTT after weaning revealed no difference in glucose between P-D and P-P. In contrast, “restricted” S-P exhibited a greater maximum increment in plasma glucose than “enhanced” S-D after IVGTT at age 3 days (p<0.05). Their fasting glycemia was higher than S-S and S-D from 1 month to 18 months of age and clamps on day 200 demonstrated higher insulin sensitivity compared to S-D and P-P (p<0.05). Data are not available beyond day 200 in this group. In conclusion, fetal growth manipulation induced different adaptive responses in postnatal glucose metabolism until 18 months of age. “Restricted” S-P foals appear to favour glucose accessibility with higher fasting glycemia than S-S controls and “enhanced” S-D, but also higher insulin sensitivity compared to the “enhanced” S-D. Conversely, “enhanced” P-D foals had a lower fasting glycemia compared to P-P controls.