Cow-Calf Commentary for Iowa Cattleman Magazine
By Sarah Phelps, ISU graduate student
March 2025
Calving Distributions: Why do they matter?
A defined calving season has significant implications for a cow-calf operation's overall profitability and production. It allows for improved management practices such as vaccination protocols, providing adequate nutrition to your cow herd, and weaning a more uniform calf crop. According to USDA statistics, only 33% of U.S. cow-calf operations report having a defined calving season. There are many advantages to maintaining a defined calving season and economic benefits when the majority of calves are born early in the season. Although you may have a high pregnancy rate, if most calves are born late in the calving season, you could be leaving money on the table. Taking time to study your calving distribution may improve the reproductive efficiency of your herd and ultimate profitability.
What is a calving distribution?
A calving distribution measures the number of calves born throughout the calving season. It is typically measured in 21-day intervals mirroring the length of a cow's estrous cycle and the fact that she has an opportunity to conceive every 21 days. Benchmarks for calving distributions as reported by CHAPS (https://www.ndsu.edu/chaps/benchmarks/) show that in mature cows, 63.5% of the calves are born in the first 21 days, 88.8% by 42 days, and the majority (96.6%) of the herd calved by 63 days, assuming a 60-day calving season. CHAPS also reports a critical success factor of 88% of the calves born within 42 days of the calving season, indicating that a lower percentage would indicate a lack of reproductive efficiency and potential economic loss.
Why calving distributions matter
Your calving distribution influences production benchmarks as well as resource utilization. When considering your labor, manpower cannot be supplied economically during extended periods. Not to mention, the quality of labor is more attentive during the beginning of the season but may become fatigued and less observant as the season progresses.
Research has shown that calves born earlier in the breeding season are heavier at weaning than those born later in the season. These calves are older at weaning and have more opportunities to reach a heavier weaning weight. When these calves are followed through the feedlot, the earlier born calves had heavier carcass weight and more choice or prime grades than calves born later in the calving season. In addition, heifers born early in the calving season have been shown to have a higher pregnancy success rate and remain in the herd longer. These heifers are set up for success as they are older and heavier at weaning, older at breeding, and are more likely to be cycling by the first day of the breeding season. Heifers who calve in the first 21 days of a calving season, are more likely to remain in the herd longer than those who calve later.
The economics of calving distributions have been well documented. A group from the University of Tennessee conducted a simulation looking at the impact of calving distributions on financial return when calves were sold at weaning. They found a $18.46 per cow improvement when the calving distribution was improved from 35% born in the first 21 days to 50% of calves born.
Reviewing your calving records can help you determine your calving distribution and if adjustments need to be made. It is also advisable to analyze your calving distribution by dam age, as this can highlight any specific age group of cows that may be calving later than expected, providing insight into how to address the issue.
Management considerations
Your calving distribution is a direct result of your breeding season. For mature cows, most breeding seasons are 60 days, allowing for the potential of 3 estrous cycles. Heifers are often exposed to a shorter breeding season of 45 days, which places selection pressure on those heifers who cycle and breed earlier in the season. Maintaining a defined breeding season ensures your cows calve within a set time window.
As you transition from calving to breeding, consider the nutritional status of your cow herd. Maintaining your herd at a body condition of 5 to 6 is optimum for reproductive performance. Cows in poor body condition going into the breeding season can delay their ability to get pregnant, which results in later calving.
If your calving distribution is not ideal, estrus synchronization is a great tool to help consolidate and move your calving distribution up. Estrus synchronization can be used with artificial insemination (AI) or natural service. Multiple protocols can be utilized, and the Beef Reproduction Task Force is a great resource to compare protocols. When considering a protocol, consider your resources, such as labor, not only at breeding but also at calving time.
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