Each year the Beef Reproductive Task Force reviews research and field use of bovine estrous synchronization protocols to determine a set of recommended synchronization protocols for beef producers that will result in the most optimal pregnancy rates. This list of protocols is then published for cows and heifers and is available at the Beef Reproductive Task Force webpage or in genetics company catalogs. The protocols are outlined for step by step instructions of how to carry out each synchronization protocol, detailing the number of days required for each protocol, products needed and timing for each step. Keep in mind, there are different sets of protocols for heifers and cows due to the physiological differences in the timing of key events, such as ovulation.

Beef producers can choose from between 3 types of synchronization protocols for cows:

  1. Heat Detection: Select Synch, Select Synch + CIDR®, PG 6-day CIDR®
  2. Heat Detection and Time AI: Select Synch & TAI, Select Synch + CIDR® & TAI, PG 6-day CIDR® & TAI
  3. Fixed-Time AI: 7-day CO-Synch + CIDR®, 5-day CO-Synch + CIDR®

1. Heat Detection

Heat detection protocols work by setting cows up to show visual estrus and then be bred by an AI technician 12 hours after the onset of standing heat. In order for heat detection protocols to return acceptable pregnancy rates, cows need to be frequently monitored for visual signs of estrus over 7 to 8 days. Check cows at least 3 times per day for a ½ hour each time, with extra time spent detecting heat at sunrise and sunset as research shows that 56% of cows show heat from 6 PM to 6 AM (Hurnik and King et al., 1987). Heat detection aids are also available to assist in identifying cows in heat when no one is watching. For this reason, when using a heat detection protocols it is important to train people to look for specific signs of estrus behavior in order to detect cows coming into estrus, during estrus and after estrus (Table 1).

Table 1. Observe cows for signs of estrus during heat detection protocols.

2. Heat detection & Time-AI

Heat detection and Time-AI protocols are the same as heat detection protocol steps besides the shorter duration of time for heat detection. After the 3 days of heat detection, any animals that have not shown signs of estrus are given an administration of GnRH (product that causes ovulation to occur within 30 hours) and fixed-time AI at that time. Even though these cows may not be showing visual estrus, there is a possibility that fertilization can still occur.

3. Fixed-Time AI

Fixed-Time AI protocols are designed to breed all cows at a predetermined time. In addition, these protocols synchronize ovulation and not necessarily estrus. These protocols are more labor intensive and expensive than the previously described protocol categories, as they require more trips through the chute and injections. However there is no heat detection with these protocols as cows are set up to all be bred at the same time. Therefore, value of labor saved not heat detecting can go towards funding these more intensive protocols.

Cow Criteria

In order for these recommended protocols to be most effective, cows should meet some minimum qualifications before beginning an estrous synchronization protocol. Body condition score (BCS) is important for reproductive efficiency; therefore, cows should be in a BCS of 5 at protocol initiation. Moreover, cows should be 50 days postpartum before starting protocols. By waiting 50 days after calving, cows should have completed uterine involution and resumed fertile estrous cycles which will give them better chances of conceiving than if started earlier.

Want Help?

There are several steps to each protocol that must be carried out correctly in order to achieve the best pregnancy rates possible. Yet, we know mistakes happen and environment cannot be controlled. Therefore, in order to assist producers in scheduling estrous synchronization protocols, the Beef Reproductive Task Force has a free Estrous Synchronization Planner available to download in Excel . This program allows producers to select the specific protocol they want to use, date to breed and products to use. Then the spreadsheet back calculates date to start the protocol, when to administer injections and breeding, and even when to turn in the cleanup bull. Once complete, a check list and calendar can be printed out for easy access.

Contact an SDSU Extension expert if you’d like assistance setting up an estrous synchronization protocol for your herd.

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