Calving distribution and its importance

Producer Question from 2015

Q:  How is calving distribution calculated and how important is it? (June 18, 2015)

A:  Calving distribution is the number of cows calving in 21-day periods during the calving season. Standard Production Analysis Guidelines indicate there are two ways to determine when to start the first 21-calving interval:

  • When the third mature cow (3-years-old or older) has calved
       or
  • Start the first 21-day calving period 285 days after the start of the breeding season.

Spring-calving cows that calve in adequate body condition (BCS = 5) tend to breed and calve earlier in the calving season and have calves that are older and heavier at weaning compared to those cows that breed later.  In a cow herd that calves in a short calving period, most cows are in a similar stage of production and it is easier to develop rations that meet the requirements of the majority of the cow herd.

There are data where the researcher tracked male and female performance by whether calves were born in the first, second, or third 21-day period of the calving season. Male calves that were steered and data recorded from birth to harvest indicated calves born the first 21 days of the calving season had a significant advantage compared to calves born in the second or third 21-day period.  Early born calves were heavier at weaning, had more carcass weight at harvest, and more had a USDA Marbling Score of Modest or greater (grading Choice or Prime) when compared to calves born in the second or third 21 days of the calving season.

Heifers born in the first 21 days of the calving season had several advantages when compared to those born in the second or third 21-day period.  Early born heifers

  • were heavier at weaning,
  • were more likely to be cycling at the beginning of their first breeding season,
  • had higher pregnancy rates than heifers born in the third 21-day calving period, and
  • more calved in the first 21-day period of their initial calving season.
Another big data set indicates that when a heifer initially calves during the first 21-days of the calving season she is more productive and stays in the herd for more years than females that initially calve during the second or third 21-day periods of their first calving season.

Through 6 calf crops, replacement heifers born in the first 21-day period of the calving season as calves went on to wean heavier calves as cows than heifers retained as replacements that were born in the second or third 21-day period.

For a commercial cow/calf enterprise this means potentially fewer replacements are needed, more calves and weight are available to sell at weaning, and a higher proportion of the herd are mature cows, which is the most productive part of the cow herd.

Dr. Rick Rasby
Professor of Animal Science
Animal Science
University of Nebraska–Lincoln