When a chicken egg starts to develop, the proteins inside the egg white change differently depending on whether the egg is fertilized or not — the embryo seems to change how these proteins break down and stick together.

Scientists found that as a chicken embryo grows inside the egg, the proteins in the yolk change a lot—13 of them become more or less common—showing the yolk is being used up and transformed to feed the growing chick.

When a hen’s egg is fertilized and starts growing into a chick, the proteins in the yolk change in specific ways—some increase, like ovalbumin, while others, like riboflavin-binding protein, decrease after about two weeks. This suggests the growing embryo is reshaping the yolk’s nutrients to support its development.

When chicken eggs start to develop, the white part changes and forms new protein teams that might help the baby chick grow — not because of food, but because these proteins are changing and working together in new ways.

In chicken eggs during the first week of incubation, the main egg white protein breaks down faster than expected, and new protein groups form—including one that teams up with a molecule that binds RNA—hinting that the egg is preparing for the chick to grow, not just storing food.