She will come into heat approx. 30-45 days following calving, then come into heat approx. every 30 days thereafter until she is bred assuming no problems that will interfere with her heat cycles such as very fat, very thin, cystic ovaries, etc. Heifers will begin cycling somewhere between 4-5 months of age (the exception rather than the rule), and 7-8 months of age (usually the norm - at least with our herd), and will continue to cycle roughly every 30 days until bred.