We hypothesized that, as the supply of preformed glucose diminishes during development, the embryo would transition to a greater rate of gluconeogenesis (GNG) and that GNG would be greater in embryos from small vs. typical size eggs. Gluconeogenesis by embryos from small (51.1 +/- 3.46 g) and typical size (65 +/- 4.35 g) broiler breeder eggs was measured by dosing [(13)C(6)]glucose (15 mgxegg(-1)) into the chorio-allantoic fluid for 3 consecutive days to achieve isotopic steady-state before blood collection on embryonic day (e) 12, e14, e16, and e18 (4 to 5 eggsxsize(-1)xd(-1)). The (13)C-Mass isotopomer enrichment of blood glucose was determined by gas chromatography-mass spectrometry. On e14, e16, and e18, but not on e12, embryos from small eggs weighed less (P < 0.05) than typical size eggs. For both sizes of eggs, blood glucose concentration, glucose entry rate (g.d(-1)), and Cori cycling and glucose (13)C-recycling (% of entry rate) increased (P < 0.05) with development. On e12 and e14, rates of glucose entry and Cori cycle flux were greater (P < 0.05) for embryos from small eggs. When standardized to BW (g.100 g of BW(-1)xd(-1)), glucose entry and Cori and non-Cori cycle fluxes were greater for embryos from small eggs. From e12 through e18, blood concentrations of gluconeogenic AA (threonine, glutamine, arginine, proline, isoleucine, and valine) were 25 to 48% less (P < 0.01) in embryos from small eggs. In conclusion, embryos from small eggs exhibit greater rates of GNG earlier in development compared with typical size eggs and, perhaps as a consequence, their reduced embryonic growth may result from diverting greater supplies of AA toward GNG.