A heifer is ready to breed when it is sexually mature and when its body is prepared to take on the strain of carrying a calf. Most heifers reach this point at about the age of one year or a few months afterward.
Farmers seek to have their heifers at a certain target weight, often 65% of the breed's average mature weight, before the heifer is allowed to breed. The heifer usually reaches this target weight either very shortly after puberty or within a few months. Having the heifer at the target weight during its first oestrus cycle optimizes its breeding ability and ensures a safer pregnancy for heifer and calf.