Abstract: A method of enhancing the growth of a bird is described. The method comprises (a) administering a compound selected from the group consisting of IGF-1, IGF-2 and active analogs thereof to a bird in ovo; then (b) incubating the bird to hatch; and then (c) growing the bird for at least three weeks after hatch. The compound is administered in ovo in an amount sufficient to enhance the growth of the bird at least three weeks after hatch. Preferred birds for practicing the present invention are chickens, and preferred compounds for practicing the present invention are IGF-1 and analogs thereof. The use of IGF-1, IGF-2 and active analogs thereof for the preparation of a medicament for administration to birds in ovo to ehance the growth of the bird at least three weeks after hatch is also disclosed, along with the pharmaceutical formulations so prepared.