Abstract: Previous studies in this laboratory have demonstrated that peptide YY (PYY) administration to turkey poults at d25 of incubation enhances intestinal Na-dependent active glucose uptake. This study was designed to further characterize the ontogeny of glucose transport in embryonic and hatchling poults and to investigate the effects of PYY on this process during development. In Trial 1, 20 turkey eggs were randomly selected at days 20, 23, and 26 of incubation, as well as the day of hatch. Hatchlings were cervically dislocated and the body weight, jejunal length and jejunal weight were recorded. Jejunal glucose uptake was estimated by measuring 3H-3-O-methyl-D-glucose accumulation in 2 mm jejunal rings in vitro. Jejunal O2 consumption was measured in vitro on jejunal rings using an O2 probe. In Trial 2, 40 turkey eggs were randomly selected at days 20, 23 and 25 of incubation and injected, via the air sac, with either 0.9% saline or 0.9 % saline plus 400 μg PYY/kg egg weight. Embryos from each treatment were harvested on days 23, 26 and day of hatch. Measurements and analyses on jejunal tissue were conducted as in Trial 1. In Trial 2, embryonic weight and jejunal weight adjusted for body weight increased (p< 0.05) with stage of incubation, while adjusted jejunal length decreased (p< 0.01). Active and total glucose uptake and jejunal O2 consumption increased with age (p< 0.05). The energetic efficiency of glucose uptake increased (p< 0.05) between d26 and hatch. In Trial 2, PYY failed to significantly affect body or jejunal weight, glucose absorption, and O2 consumption at any stage of development. PYY did however, decrease the efficiency of glucose uptake at d26 and at hatch (p< 0.05). In contrast to earlier investigations using higher dosages of PYY, this study demonstrated that in ovo PYY administration at 400 μg/kg egg weight has little effect of jejunal function in turkeys.