The Jewish historian Josephus writing in the first century records that at Passover up to 265,000 lambs would be sacrificed in the Jewish temple at Jerusalem.
The Passover lamb was called “The Lamb of God.”
Those lambs had to meet the strict legal-religious regulations of the Jewish faith. They had to be no more than one year old, male and without spot or blemish. Therefore they had to be born in controlled conditions and inspected for birth defects before being raised in protected conditions.
Where did they get that many lambs? The law also said that animals to be sacrificed had to be born within five miles of Jerusalem.
Bethlehem is just five miles from Jerusalem.
The hillsides around Bethlehem, therefore were a first century lamb factory farm. When the lambs were born they were wrapped up in strips of cloth to protect them and placed in a stone feeding trough in the birthing barn until the priest could come by and inspect them.
This is why the angel said to the shepherds “This shall be a sign for you. You will find the baby wrapped in swaddling clothes and lying in a manger.” The “manger” was most likely a stone feeding trough, not a wooden crib as we usually see. That comes from the medieval version of the story.
Jesus was therefore born in the same place and at the same time with the same treatment as the lambs that would be sacrificed.
The shepherds knew they were not going to see just any baby. They were going to see the newborn Lamb of God.
That’s why they worshiped him. They knew he was the promised Messiah, the Suffering Servant, the Lamb of God.
— Source unknown.