Ontogeny of energy and carbohydrate utilisation of the precocial avian embryo and hatchling

Unlike the mammalian fetus, the developing chick embryo must rely upon the nutrients provided by the egg independently of maternal influence. Nutrient transfer from the mother to the embryo is completed before the egg is laid, with the egg containing all the nutrients needed for embryonic growth and development. The in ovo nutriture of the chick embryo consists mainly of yolk fat with traces of carbohydrates. However, glucose is the primary source of energy needed to fuel embryonic development and growth.Therefore, the avian embryo relies upon hepatic gluconeogenesis as the primary mechanism for glucose production. The gluconeogenic pathways are highly active during embryonic development and decline post-hatch. Post-hatch, glycolysis is critical for the survival of young hatchlings, while poults are adapting to an external carbohydrate-rich diet. It is often during this critical post-hatch period that glycogen reserves are rapidly depleted and may adversely affect growth and increase early mortality. However, with immediate access to feed, hatchlings may replenish their glycogen reserves, providing the energy needed for optimal growth performance post-hatch.