Cattle producers often associate estrous synchronization with artificial insemination (AI). Many do not associate the practices and economic benefits of synchronization with natural service breeding programs.

“There are many production and economic advantages to utilizing synchronization in the cowherd,” says Lisa Pederson, North Dakota State University Extension livestock specialist at the Central Grasslands Research Extension Center. “Mainly, it creates a more uniform calf crop.”

Synchronization protocols, whether used with AI or natural service, synchronize the estrous cycles of females into a tighter period. This allows the majority of the cowherd two opportunities to become pregnant within the first 30 days of the breeding season. Therefore, synchronization improves uniformity of the calf crop by increasing the percentage of calves born within a shorter timeframe.

With more calves born in a shorter timeframe, producers can sell larger groups of calves at a similar weight, says Pederson. Studies show a significant price advantage when marketing larger drafts, or groups, of calves of a uniform weight. Additionally, calves born earlier are heavier at weaning. For example, calves born on the first day of the calving season will weigh approximately 50 pounds more than calves born on day 21, 100 pounds more than calves born on day 42 and 150 pounds more than calves born on day 63.

“There are true economic and long-term production advantages to calving more of the herd earlier in the calving season,” says Pederson. “Calves will be more uniform at weaning, and heifers retained as replacements will be more productive.”

Because synchronization protocols used with natural service were developed so several females would come into heat over a short time period, it is important to choose the proper bull-to-cow ratio, says Pederson. Research in this area indicates an optimal bull-to-cow ratio to range from 1:16 to 1:25; however, ranchers should take pasture size, distance to water, topography and the protocol used into consideration. All sires should undergo a breeding soundness exam regardless of the breeding strategy, and it is also recommended that sires used in synchronized herds be at least 2 years old and be observed when introduced to the cow herd to ensure adequate libido.

There are four synchronization protocols approved and designed for use with natural service (NS) breeding programs: 1 shot Prostaglandin (PG) and NS; 7-day controlled internal drug release (CIDR) and NS; 14-day CIDR and NS; and 14-day melengestrol acetate (MGA) and NS (for heifers only). When deciding which protocol to use, Lacey Quail, NDSU Extension livestock management specialist at the North Central Research Extension Center, advises ranchers consider several factors.

Labor demands are the most common reason for not utilizing synchronization. Thus, the time required to pen, sort and/or handle cattle through working facilities should be seriously considered. Natural service synchronization protocols vary in their labor requirements from zero (14-day MGA and NS) to one (1 shot PG and NS) or two (CIDR and NS) handling events.

While the 14-day MGA and NS protocol for heifers does not require handling through working facilities, it does require diligent feed and bunk management. Because MGA is an oral synthetic progestin, it is delivered as a feed additive.

“It is critical that heifers receive the same amount of MGA each day to properly control their estrous cycle and maximize pregnancy success,” says Quail.

Therefore, operations already feeding a total mixed ration to heifers often incorporate the 14-day MGA and NS protocol. It is not recommended that MGA be used when the amount consumed by each heifer cannot be controlled well. If heifers consume too little or too much MGA, they may show heat earlier or much later, respectively, than planned. Both scenarios result in heifers that are not synchronized with the rest of the group (which is what a producer paid and planned for) and can result in decreased pregnancy rates. If bunk space is limited or feed timing is inconsistent, a different synchronization protocol may be a better fit.

While synchronization protocols using a CIDR insert are more expensive and require more handling, they can be used in both cows and heifers, and the efficacy of a CIDR is not dependent on feed activity or bunk management. On the other hand, the 1-shot PG and NS protocol is simple and inexpensive; however, it is only effective in cows and heifers that are already cycling. If many heifers have not reached puberty or cows have not started cycling again after calving, protocols including MGA (heifers only) or a CIDR (heifers and cows) are the best option, as they have been proven to induce cyclicity. Research shows that females not cycling by the start of the breeding season are less likely to become pregnant and calve early, impacting profitability.

Synchronization protocols used with natural service breeding programs vary from five to 28 days from start to finish, so they require diligent planning to be successful. For example, if a producer plans to turn bulls in on June 1 for March calves and would like to use the 14-day CIDR and NS protocol, they need to start the protocol on May 4, (nearly a month ahead of time). Last-minute planning can be very detrimental to breeding success. Planning ahead and precisely following the protocol as it is written are critical to successfully implementing synchronization into any management system.

There are great tools out there to help, says Quail. Contact your county NDSU Extension agent, state livestock specialist or herd veterinarian to ask questions.

“When it comes to synchronization, it’s better to ask questions beforehand than it is to realize a mistake later and worry about how it might impact pregnancy rates that year,” says Quail.

The Beef Reproduction Task Force, a multi-state team of researchers and Extension specialists, offers estrous synchronization planning tools, protocols and other resources to help manage the breeding season at https://beefrepro.org/resources/.

NDSU Agriculture Communication – April 29, 2025

Source: Lacey Quail, 701-831-0414, lacey.quail@ndsu.edu

Source: Lisa Pederson, 701-424-3606, lisa.pederson@ndsu.edu

Editor: Dominic Erickson, 701-231-5546, dominic.erickson@ndsu.edu