Charles Ellicott Commentary Leviticus 22:27

"When a bullock, or a sheep, or a goat, is brought forth, then it shall be seven days under the dam; and from the eighth day and thenceforth it shall be accepted for the oblation of an offering made by fire unto Jehovah." — Leviticus 22:27 (ASV)

When a bullock, or a sheep, or a goat— The three sacrificial quadrupeds (see Leviticus 22:19 and Leviticus 17:3-6).

Is brought forth. — From this expression, it was enacted during the second Temple that an animal fit for sacrifice had to be born naturally. One brought into the world by artificial aid was disqualified for the altar.

It shall be seven days under the dam. — An animal younger than seven days is extremely weak and unfit for human food, and therefore must not be offered as the food of God, as sacrifices are called .

For the same reason, children could not be circumcised before the eighth day from their birth .

Because the text here says that the newly born animal is to be with the dam for seven days, it was enacted that if the mother died before the seven days were complete (in which case the young animal could not be with the dam for the full seven days), it was forever disqualified as a sacrifice.