Nearly 40% of beef producers who don’t use AI indicated that labor and time were the most common reasons for not using AI, according to USDA survey data. Other reasons for not using AI include difficulty or complication (20%), cost (13%), lack of facilities (7%), and a belief that “it does not work” (3%).

The use of AI alone (with no clean-up bulls) to get all of your cows bred during the breeding season is probably unrealistic on most commercial cow/calf operations, since it requires a long period of heat detection (upwards of 45 to 60 days). Instead, many cow/calf producers synchronize estrus and AI their cows once prior to turning out clean-up bulls. There are many options available to implement this system of “AI + natural service” on cow/calf operations.

Proven Protocols

Over the past several decades, well over 50 different estrous synchronization protocols have been developed and tested in cowherds. Many protocols effectively synchronize a large percentage of the cowherd and lead to reasonable pregnancy rates.

However, since several variables are involved in synchronization protocols (types of drugs used, timing of injections, timing of fixed-time AI, heat detection vs. mass insemination, etc.), it can be difficult for producers to choose the best option for their operation – many producers are overwhelmed with too many options.

University researchers have recently “recommended” several proven protocols for commercial cow/calf producers to use on their cows and heifers. The Beef Reproduction Task Force, a group of beef cattle reproductive specialists, annually publishes a list of these proven protocols on their website.

The protocols identified by this group are proven, require working cattle three times through a chute (maximum), are affordable, and are relatively easy to accomplish. If properly implemented, they can consistently yield acceptable rates of estrus (“heat”) and pregnancy. The average pregnancy rates reported for these protocols ranges from 46 to 68% in cows (based on data from 14,203 cows) and 45 to 61% in heifers (based on 12,280 heifers).

There are other protocols that can attain similar estrus and/or pregnancy rates; however, they have not been researched or proven as extensively.

Decision #1: Should I Detect Heat, Time-Inseminate, or Both?

When thinking about which protocol to use, first consider the variables that can be altered. Some protocols are designed for producers who check heat and AI only after heat is detected. In contrast, other protocols are designed for the mass-insemination (or fixed-time insemination) of cows at a specific time after the final treatment is given (regardless if heat is observed or not).

Some protocols merge these two options and include both a time period when cows are inseminated once detected in heat, and also a pre-determined time when all cows not yet observed in heat are mass-inseminated. The decision of whether to detect heat, mass-inseminate, or both will affect the overall cost and the amount of labor needed to implement the protocol.

Decision #2: Should I Use Progesterone or Not?

Progesterone sources are incorporated into synchronization protocols to increase the effectiveness of the protocol, and get more cows to come into heat and/or become pregnant. Progesterone has been included into several protocols to get all cows to come into heat during a shorter time frame, and thus make mass-insemination more effective by reducing the number of cows that come into heat early.

Progesterone can be fed to cows as melengestrol acetate (MGA) in a feed supplement, or given through a controlled internal drug release (CIDR) device inserted into the vagina for a 7-day period. However, some protocols successfully synchronize cows without the use of any progesterone. These protocols are often cheaper and require less labor, but in some cases they might not be as effective.

Decision #3: Which Protocol Should I Use?

Choosing the best protocol for your operation depends on several factors. For example, the number of days before the breeding season that a protocol needs to be started is a major factor (e.g. MGA Select requires starting 33 days before breeding, while Select Synch only requires 7 days), so planning ahead is vital. In addition, the ability to feed MGA to cows daily vs. simple insertion of CIDRs for 7 days should be considered.

In general, most producers consider cost and labor as the 2 major factors when deciding which protocol to use. Addition of the CIDR into a protocol will increase the cost, as will the incorporation of MGA since there is a cost associated with feeding it. Labor also increases when MGA is fed, and when heat detection is incorporated into a protocol.

Decision #4: When Should I Turn Out Bulls?

The majority of producers who utilize an estrous synchronization protocol AI their cows only once soon after the protocol is completed. And, clean-up bulls are turned out beginning about 10 days later and typically left with the females for another 45 to 60 days to impregnate animals that did not conceive to AI. However, researchers have explored incorporating the use of natural service in partial replacement of AI.

Researchers Ron Torell, University of Nevada, Elko, and David Bohnert, Oregon State University, Burns, attained very impressive first-service pregnancy rates of up to 70% by incorporating the use of bulls into synchronization and mass-insemination protocols. Two protocols were evaluated in over 1,200 well-developed yearling heifers from 4 cooperating ranches. Their goal was to get as many heifers pregnant as possible as a result of estrous synchronization (with the majority being bred to AI) while minimizing cost.

The heifers were synchronized with the CO-Synch + CIDR protocol (details available on the website mentioned above), and all heifers were mass-inseminated via fixed-time AI at about 65 to 70 hours after CIDRs were removed. However, in order to avoid “missing” heifers that came into heat much earlier or much later than this time frame, all heifers were exposed to fertile bulls (1 bull to 15 heifers) during 2 periods after CIDR removal: for the 48-hour period immediately following CIDR removal, and beginning 84 hours after CIDR removal. Bulls were removed from heifers between 48 and 84 hours after CIDR removal, when most heifers actually came into heat so that mass-insemination could be done. It would be unrealistic to depend on bulls to breed heifers during this period of widespread estrus – physical injuries to bulls and missed cows would result. At the four locations, the first-service conception rate ranged from 50 to 70%.

Unfortunately, this strategy does not allow a producer to distinguish between calves sired by AI sires vs. natural service. However, if sire identification is needed, a different breed of bull could be used for AI compared to natural sire (e.g. Angus bulls for AI, and Hereford bulls for natural service).

The goal of this protocol was to get as many heifers bred in the first cycle as possible, without having to check heats. Maximizing the number of heifers that conceive early in the breeding season can increase the number of calves born early in the calving season and eventually yield more pounds of calves to sell at weaning

Additional Resources Available

In addition to the protocols listed above, other resources are available. The Iowa Beef Center has an “Estrous Synchronization Planner” available via CD which can help producers customize a breeding schedule and help to make the implementation of synchronization and AI easier. This Microsoft Excel spreadsheet contains five worksheets, including: program, tips and overview, planner worksheet, printout, and calendar. Click here for more information.

The Bottom Line

Detailed information on numerous proven estrous synchronization protocols is now readily available to cow/calf producers. Consistent pregnancy rates to AI of 45 to 65% can be readily achieved in cows and heifers, depending on the use of heat detection with AI, fixed- time AI, or a combination of both. Further, incorporation of progesterone has improved the synchrony of females, reduced or eliminated the need to detect heat, and made fixed- time insemination more successful. And, use of bulls after estrous synchronization (just before and just after mass-insemination) in beef heifers has resulted in pregnancy rates up to 70%. Regardless of which option is chosen, it is vital for a producer to be well prepared before implementing an estrous synchronization protocol by accessing information on-line or working with a local University Extension Educator or licensed veterinarian.