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Tightening up Calving Season

Originally written by Olivia Amundson, former SDSU Extension Cow/Calf Field Specialist.

One of the most important indicators of success in a cow-calf herd is reproductive efficiency of that population. A major profit-determining factor is the percent of calf crop weaned. This is accomplished through incorporating a shortened and defined breeding and calving season. According to USDA APHIS, (2008) 54.5% or one-half of operations from 24 states failed to have a defined breeding season. Cultivating uniformity of a calving season can be the first step toward improving production efficiency.

What is calving distribution?

Calving season can be defined as the number of calves born within a 21-day calving period. Ideally, 60% of the herd should calve within the first 21-day period. According to the Standard Production Analysis Guidelines there are two ways to start the first 21-day calving interval:

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

How do we fall out of a shortened calving season?

Cows fall out of a defined calving season for multiple reasons. Reproductive failure is the number one reason cows are culled from the herd. Instances such as illness, injury, poor cow nutrition, depressed body condition score, and extreme weather events are some reasons cows fail to rebreed or become pregnant late in the breeding season. If there is not a defined calving season in place cows slowly fall farther and farther out of the assumed calving period.

Why is it important?

Uniformity of calving produces multiple benefits for the production herd. Calf crops more uniform in size and age have market advantages and exceed returns over calves that lack uniformity in both age and weight. Calves from these females produce heavier unadjusted weaning weights for the first six parturitions. Furthermore, at weaning, one day of age difference translates to 2.4 lbs of weaning weight lost.

Female progeny born within the first 21-day period have also demonstrated benefits compared to females born in the second or third 21-day period. Heifers born early:

  • Had increased weaning, pre-breeding and pre-calving body weight,
  • Greater percentage cycling at beginning of breeding season,
  • Greater pregnancy rates,
  • Larger percentage of these females calved in first 21-day period of their initial calving season.

Male progeny born in the first 21-day period preformed greater compared to calves born in the second and third 21-day periods. Steers born early:

  • Had increased weaning weights,
  • More ideal marbling scores (grading Choice or Prime),
  • Overall, positive effect on feedlot and carcass performance.

Implementation of a shortened calving season provides opportunity to facilitate improvements in herd health and management. Labor and resources during a defined calving season can be managed more intensively to decrease labor requirements and enhance overall efficiency. Likewise, timing of vaccinations are more adequately scheduled as a result of uniformity of the herd. More intense observation of the cow herd during a shortened calving season due to greater allocation of time and resources allows for a reduction in calf losses. This is significant as one of the profit-determining factors in cow-calf operations is percent of calf crop weaned.

Finally, through grouping of cows based on stage of gestation, improvement of heifer and brood cow nutrition can be accomplished. Independent of which calving season a herd falls into, having a defined breeding and calving season allows for a better representation of nutritional needs. Cows strung out within the breeding and calving season are harder to provide adequate nutrition to. For an economic review regarding calving distribution see article, Bunch the Cow Herd.

How can we implement strategies to tighten our calving season?

Environmental challenges, including mud and a wet spring pose challenges to producers as they prepare for the upcoming breeding season. Advances in reproductive technologies can help decrease breeding time as well as increase the proportion of cows that conceive in the first 21-days of the breeding season. Successful control of estrus in well-managed herds can shorten the breeding season dramatically while increasing the uniformity of the calf crop.

The primary way to group calving is through synchronization of estrus with incorporation of AI or natural service (NS). Incorporation of a synchronization program every year will progressively increase the number of cows calving earlier in the breeding season. In herds where calving season is strung out for >120 days, incorporation of two synchronization periods 20 to 30 days apart will help move up late calving cows.

An ideal breeding consists of a 60-90-day breeding season. For guys that put the bull out longer than the ideal breeding season, consider pulling the bull around 60 days to help shorten the following calving season. Those who use natural service (NS) also have the opportunity to incorporate simple synchronization protocols to ensure a tightened calving window. Protocols such as a 7-day CIDR with NS or a 1-shot prostaglandin can help move up some of those late calving cows. When using estrous synchronization ensure the bull to female ratio is 1:15 to 1:25. If a situation arises and cattle go off feed or we are blessed with a rain or snowstorm, modifying the original protocol may be permitted.

Consider where you will breed cows and make a game plan. If your usual workspace is in an area of water and mud, consider using portable facilities on higher ground to get cows synched and bred. If this isn’t an option, it may be an opportunity to consider time of calving. Pushing calving back is easily accomplished and allows for a more desirable and dryer time to breed cows, however, several considerations need to be reviewed before changing the calving season.

If setting up cows is not an option due to time and labor, facilitating the use of AI technicians to breed the herd can help manage that breeding period. This decreases the amount of personal time and stress required to accomplish a set breeding period and permits herd improvement. When considering incorporating estrus synchronization, consider when you want the calving season to occur.


Implementing a controlled calving season is important for the profitability and lifetime productivity of the herd. Recognizing the effect of a spread-out calving season and incorporating reproductive technologies and management strategies to tighten calving can contribute economic benefit to the operation.