Leviticus 22:27

When a bullock or a sheep or a go at is brought forth, then it shall be seven days under the dam, to get its nourishment from its mother; and from the eighth day and thenceforth it shall be accepted for an offering made by fire unto the Lord. "The reason for this was that the young animal had not attained to a mature and self-sustained life during the first week of its existence. " (Keil.) Animals became admissible for sacrifices at the same age as that when a male child was received into the covenant relationship with God by the sacrament of circumcision.