A successful breeding season requires planning. Estrus synchronization is one tool that can benefit cattle producers if used correctly. Estrus synchronization can allow more females to be bred earlier in the breeding season and can shorten the postpartum interval in late-calving females, allowing them to become pregnant earlier in the calving season.

Increasing the number of heifers and cows bred early in the breeding season translates to more calves born early in the calving season. Calves born at a similar age tend to be a similar weight and size, resulting in a more uniform calf crop at weaning. Cows calving early in the calving season have more time to resume cyclicity before the breeding season, allowing them to be more likely to become pregnant early on.

Estrus synchronization can be used with natural service (bull-bred) herds, as well as facilitate the use of artificial insemination (AI). Artificial insemination allows producers to use proven bulls they might not normally afford to make genetic advancements to their herd.

When selecting an estrus synchronization protocol, consider the number of days a protocol requires, the condition of the facilities being used, the labor and skill needed and/or available, the number of times females will be run through a chute, and of course, cost.

Many estrus synchronization protocols exist for cows and heifers. The most current protocols can be found at the Beef Reproduction Task Force site (beefrepro.org). When reviewing protocols, they can be divided into controlled internal drug release (CIDR) protocols and melengestrol acetate-prostaglandin (MGA-PG) protocols. Please note MGA-PG protocols are labeled only for use in virgin heifers. The advantages and disadvantages of both types of protocols are below.

Controlled Internal Drug Release (CIDR)

A CIDR is a T-shaped device that releases a constant dose of progesterone. Progesterone is the hormone responsible for maintaining pregnancy, but when used in a synchronization protocol, it prevents estrus. Using CIDRs provides some flexibility in controlling estrus with protocols available for 5, 7, or 14 days.  In addition to controlling estrus in cycling heifers, a CIDR has been shown to initiate puberty in prepubertal heifers and cyclicity in anestrus cows. More information on managing postpartum anestrus cows can be found in a recent article, Managing Postpartum Anestrus in Beef Cows for a Successful Breeding Season.

Disadvantages of using CIDR-based protocols include the number of times cattle will be handled through a chute and the labor required for those trips. At the time of this article, CIDRs cost roughly $14 to $15 per insert. The CIDR protocol requires more trips through the chute than a protocol that utilizes melengesterol acetate (MGA), another source of exogenous progesterone that can be utilized in heifers.

Melengestrol Acetate (MGA)

Melengestrol acetate, or MGA, is an orally active progestin and is labelled for use in heifers to suppress estrus. For this protocol, the target feeding rates are 0.5 mg/day per heifer for 14 days, followed by a prostaglandin (PG) injection 19 days later. Please note 2 to 3 days after the MGA feeding period, heifers will likely exhibit estrus behavior. This is a sub-fertile heat and heifers should not be bred. The primary advantages of using MGA are cost and simplicity. The MGA-PG protocol (Figure 1) requires one trip through the chute to administer PG and a second trip if using AI.

Using MGA to synchronize estrus requires consistent consumption and delivery during the 14-day feeding period. In addition, this is a much longer protocol (39 days when using AI) compared with other synchronization protocols. Keep in mind the feeding/labor costs associated with delivery of the product in a bunk to evenly distribute the product.

Key considerations

Protocols are generally developed to be utilized with heat detection and artificial insemination (AI) but can be used with natural service as well. Protocols can be broken down into three main groups: 1) heat detection and AI, 2) heat detection and timed AI (TAI), and 3) fixed-time AI. For protocols involving heat detection, heifers should be inseminated 12 ± 2 hours after detection of standing estrus. Heat detection and timed AI (TAI) protocols involve AI  12 ± 2 hours after observed estrus for 3 days, after which time any non-responders will be timed AI bred 72 to 84 hours after prostaglandin (PG) with GnRH given at TAI. For heifers, pregnancy rates from current TAI protocols tend to be 5 to 10% lower than using heat detection alone. Generally, fixed-time AI protocols are considered based on the number of females to inseminate, labor, and facilities. For more information on estrus synchronization protocols, read this past article.

While any of the heat detection protocols can be utilized with natural service, the one-shot prostaglandin (PG) protocol is an option that can increase the number of cows coming into estrus early in the breeding season with decreased labor and expense as it only requires a single shot of PG and one time through the chute. This protocol calls for bulls to be turned out and then 5 days later, a single PG shot is given to synchronize a majority of the cows. Read more about this option in a past article.

Considerable research and field data support the use of these protocols. General comparisons of protocols used for beef heifers can be found in Table 1.

Estrus synchronization protocols

One of the major considerations to think about when feeding MGA is bunk management and delivery. The proper dosage is critical for success of these protocols. Poor bunk management leads to inconsistent intakes and consequently inconsistent results. By ensuring that there is adequate bunk space (generally allowing two feet per head), you are providing heifers the opportunity to equally consume targeted intakes.

Final thoughts

Overall, an operation’s ability to provide proper labor, facilities, and experience will dictate which protocol can be efficiently carried out to successfully synchronize females. Furthermore, ensuring heifers are in adequate body condition and have proper nutrition and health management will significantly contribute to the success of synchronization and pregnancy.

To generate calendars specific to the timing of synchronization drugs, CIDR insertion and removal, and when to artificially inseminate, producers can utilize the Estrus Synchronization Planner. Another resource to evaluate costs associated with different protocols and breeding decisions would be the Breeding Cost Cow-Q-Lator. For more resources and information on synchronization protocols, visit https://beefrepro.org/resources/ or contact your local extension personnel to help find the protocol best suited for your operation.