Why do you have to feed a baby calf with a bottle?

The only way to get milk is for a female cow to have a baby. And like all mammals the mother produces milk for the young. Then the baby will be taken away at birth so that we can get the milk that was meant for a baby. It's still a baby, so it still needs milk. That's where we come in. We have to bottle feed it, so give it a bottle full of milk.

The above is for dairy calves. For beef calves, baby orphan calves that cannot be grafted onto another mother must be fed milk to help them grow. Calves' stomachs, when born, are like a monogastric's stomach and the rumen doesn't start developing until around 4 weeks (30 to 35 days) of age. Milk is the only source of protein and energy that calves need to survive and grow on efficiently.