The Bible doesn't mention a stable in connection to Christ's birth.

It simply mentions a manger.

 

Scripture reports that they laid Jesus in a manger because there was no room for Him in the guest room. The Greek word used in Scripture is 'kataluma' and can mean guest chamber, lodging place or inn. The only other time this word was used in the New Testament, it means 'a furnished and large upper floor room within a private house'. It is translated guest chamber (guest room), not inn (Mark 14:14-15).

According to Bible archaeology experts, Jesus was probably born in the house of relatives, but outside (under) the normal living and guest quarters.

In ancient Israel, many people held their animals (or at least some animals) in the ground floor of their house. So it's indeed possible, although not mentioned, that baby Jesus was surrounded by animals. The fact that peope held animals in their homes, explains why Jesus was laid in a manger.

 

We come to the conclusion, that Jesus probably wasn't born in a stable, barn or cave. He rather was born in the house of Joseph's relatives, on the ground floor, for the was no space left on the upper floor (where rooms were located).