A:   The post-partum interval (the interval from calving to the first heat or estrus after calving) will be between 50 and 55 days for mature cows, if she is in good condition at calving and she experiences no calving difficulty. First-calf-heifers will have a 10 to 15 day longer interval. If they calve in poor body condition and have calving difficulty, you can easily add another 10 to 15 days, to first-calf-females.