First-calf heifers that become pregnant early in the breeding season for their second pregnancy have greater lifetime productivity and longevity than those who don’t become pregnant until later in the breeding season. Because a year lasts 365 days and pregnancy lasts about 285 days, cattle must become pregnant within 80 days after calving in order to maintain a 365-day interval between calvings. 

Although a high percentage of adult cows in good body condition are expected to resume fertile cycles within 80 days after calving, the length of postcalving infertility in first-calf heifers is often longer than mature cows in the same herd. Therefore, many producers prefer to breed heifers to calve several weeks before the mature cows begin their calving season. 

Studies have indicated heifers that calved early produced greater lifetime calf weaning weight due to being more likely to remain in the herd and the fact that their calves are older at weaning compared to heifers that conceived later in their first breeding season. Many studies support the importance of selecting bred replacement heifers that will calve over a short calving season that either starts before the start of the mature cow calving season or that is confined to the first few weeks of the mature cow calving season. 

In order for first-calf heifers to give birth to their first calf at about 22 to 23 months of age so they have 90 to 100 days between calving and the start of the next breeding season, they must become pregnant by 12½ to 13½ months of age. Fortunately, the average age at which beef heifers reach puberty should allow producers to select and manage heifers that can become pregnant in a breeding season that starts ahead of the mature cow breeding season.

Even though there are benefits to calving heifers earlier than mature cows, it is important to recognize this strategy will increase the length of the calving season, it requires heifers reach puberty at an early age and the strategy may not be beneficial if the herd experiences bull fertility or nutrition challenges. A careful evaluation of each herd’s expected length of postcalving infertility in both first-calf heifers and mature cows, age when a high percentage of replacement heifers reach puberty, and the costs associated with moving heifer breeding earlier than mature cow breeding allows producers to make the best decision for their situation. 

One study evaluated the effects of breeding heifers to calve zero to six weeks earlier than mature cows and found that if the length of the period of infertility following calving for first-calf heifers is 80 days or longer, breeding heifers to calve ahead of the mature herd resulted in: more cows pregnant in the first 21 days of breeding, more cows pregnant in a 60-day breeding season and greater total weaning weight. Interestingly, breeding heifers to calve three weeks ahead of the cows resulted in nearly as much benefit as a heifer breeding season that began six weeks ahead of the mature cows. 

By knowing an individual herd’s reproductive characteristics, the ideal length of time to start the heifer breeding season ahead of the mature cows’ can be optimized to capture reproductive benefits while minimizing cost.  

Editor’s note: Robert L. Larson is a professor of production medicine and executive director of Veterinary Medicine Continuing Education at Kansas State University in Manhattan, Kan.