Calving Distribution Affects Herd Health by: Olivia Amundson SDSU Extension Cow/Calf Field Specialist


Preparing for calving season is always a busy time of year. Depending on the time of year cows start calving will determine what type of preparations and facilities are needed. Nonetheless, cows calving within a defined calving period allow those preparations to be more focused on labor and management.

Research shows cows calving earlier in the calving season remain in the herd longer than their herd mates that calve later, but also raise heavier calves that out-perform their younger counterparts. However, an additional benefit of a defined calving season is the increased ability to manage the health of both cow and calf.

Earlier Calving Equals Better Health

National benchmarks suggest 63% of the cowherd should calve in the first 21 days of the calving season, 87% by 42 days and 96% by 63 days. Extending the calving season beyond these parameters, compromises a producer’s ability to capture the maximum value for a set of calves under most management scenarios. For more information on calving season benchmarks, refer to our article, Calving Season Benchmarks. One major benefit to a front-loaded calving season is the ease of allocating and delivering feed resources. Cows calving at similar times allow more cows to be in similar production, which in turn allows feed resources to be fed more accurately across the herd and minimizes the need for balancing multiple rations, since nutritional requirements should be relatively uniform.

Furthermore, cows receiving adequate nutrition maintain an appropriate body condition score. Cows should be managed to maintain a Body Condition Score (BCS) of 5 to 5.5 throughout the production cycle to avoid compromising reproductive success. Cows in early lactation have higher nutrient requirements, and therefore, require a greater quality and quantity of feed. When the majority of cows are calving around a consolidated time point, supplementing the increased feed required to meet requirements is streamlined and consistent. This allows for more accurate allocation of feed and helps simplify maintaining a more-consistent body condition score across the herd. It’s important to remember that even with a consolidated calving season and the correct quality and quantity of feed, without adequate bunk space (2 ft./hd.), social challenges between animals can occur, and cows can fall behind. If competition between animals continues, managing younger females separately should be considered to minimize the issue and ensure consistent feed delivery.


When the calving season is consolidated, nutritional requirements are more synchronous across the herd, and these benefits extend beyond improved feed management. When this occurs, cows are in better body condition and have the needed resources to build up a high-quality colostrum prior to calving. Body condition becomes critical for the quality of colostrum produced. Specifically, during the late gestation period, cows that are in a body condition score of 4 or lower may see some lower antibody concentrations in the colostrum. This translates to a weaker immune system from birth compared to calves with access to higher quality colostrum. For more in-depth information on colostrum quality, refer to the article, Can You “Make” a Cow Deliver Better Colostrum?. By effectively managing our females, the quality of colostrum for calves born earlier in the calving season can be maximized to help set them up for successful immunity as they continue to develop.

“You can’t manage what you don’t measure. Through focusing on consolidating the calving season, management of herd health falls in synch.”

— Olivia Amundson, SDSU Extension Cow/Calf Field Specialist


Vaccines, while important, are only as good as the management system they are provided under. The goal of any vaccine is not to prevent infection, but rather to form a robust immune response against specific organisms, should the animal become exposed. Depending on the type of vaccine, the immune system will respond in different ways. For more in depth information, refer to the article, Livestock Vaccines: How They Work and How to Ensure They Do Their Job. Vaccines work more efficiently when given at the appropriate time according to manufacturer or veterinarian recommendations. When calves are born later in the calving season, this becomes detrimental to their vaccine schedule, as well as the cows due to varying levels of immunity and responsiveness to vaccines. Pre-breeding vaccines should take place at least 30 days prior to the breeding season rather than being given at preg-check or at bull turnout. When the calving season is drawn out, this interrupts those vaccine recommendations if all cows are to be worked at the same time. The same applies with calves, if branding or turn-out shots are being given to calves with varying ages, the vaccine becomes less effective at protecting improperly vaccinated calves from future exposures.

Calf Growth

A final thought to consider is the overall potential for growth of the calves being produced. We know that calves gain approximately 2 lbs. per day from birth to weaning. Calves born later in the calving season will be lighter than their counterparts and usually sell for a lower $/Hd. price compared to calves born earlier in the calving season. Those that are put on feed can gain additional weight, however these calves will continue to be lighter than calves born earlier in the calving season, simply as a product of decreased age. Younger calves, still largely on milk, also have the chance of having an underdeveloped rumen. Older calves have had an opportunity to develop their rumen through grazing opportunities, however, when younger calves are weaned prior to this development, it becomes detrimental to the growth of the calf and its post-weaning performance.


You can’t manage what you don’t measure. Through focusing on consolidating the calving season, management of herd health falls in synch. Focusing on the foundational growth of the operation, such as front loading the calving distribution, is paramount in assessing the performance of our animals. Once these foundational components are established, producers can more easily evaluate the genetic potential of their animals by optimizing management and leveling the playing field between calves by exposing them to environmental stressors at similar stages of development. In order to improve the quality of data that we’re using to progress the cowherd, it’s very important we’re using an unbiased evaluation process to make those decisions. Having more calves of a similar age is helpful in this regard, in addition to benefiting the year-year profitability of the operation. Happy calving.


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