Here's why:
* Rumen, Reticulum, and Omasum: These are the first three chambers of a ruminant's stomach, and they're primarily responsible for digesting roughage (like grass and hay). They are not fully developed at birth.
* Abomasum: This chamber is the only one that secretes digestive enzymes and acids, and it's responsible for breaking down the milk that a calf consumes.
What happens as the calf grows:
* As the calf starts to eat solid food, the rumen, reticulum, and omasum gradually develop and begin to function.
* This process is aided by the presence of beneficial bacteria in the rumen, which help break down plant matter.
So, while a calf has all four stomach chambers at birth, only the abomasum is working. The other chambers develop over time as the calf matures and transitions to a diet of solid food.