With calving just beginning, it is hard to think about next year’s calf crop. However, with bull sales underway, the 2015 AI beef sire directories available, it is time to think about breeding season especially if you will be using synchronization. Depending on which protocol is selected, it could be over 39 days from start of the program to artificial insemination. This means, if you begin breeding May 13 for a February 10 calving date, you will need to start synchronizing heifers April 3. 

Recommended Protocols & Useful Tools

The Beef Reproduction Task Force composed of representatives of the AI and pharmaceutical companies, veterinarians and reproductive specialist have developed a list of synchronization protocols recommended for heifers, based on research data and field use. The recommended protocols can be found in the AI catalogs and on the Beef Reproduction Task Force website. Another tool proven to be handy is the Estrus Synchronization Planner, available for download on the Beef Reproduction Task Force website. It is a free download that compares synchronization protocols and develops a synchronization and breeding calendar for both heifers and cows.

Handling Tips

Take note that not all protocols are for both cows and heifers. There is a difference in physiological response between heifers and cows. It is important that you do not use a cow protocol on heifers. Likewise, follow the protocol, give the proper hormone injection or insert at the right time and don’t expect to jump start all heifers that are not cycling. Follow Beef Quality Assurance guidelines when giving injectable hormones. Giving the injection in the rump of the heifer does not increase the efficacy or speed of the hormone because it was administered “closer to the ovary”. All drugs must enter the blood system and travel to the heart and lungs before reaching the target organ (i.e. ovaries).

The adage more is always better does not work with melengestrol acetate (MGA). First, it is illegal to use MGA off label. Secondly MGA is absorbed in the fat and will take longer to clear from the heifer’s system when fed at a rate higher than 0.5 mg per head per day creating problems with estrus (heat) responses and subsequent timing of prostaglandin injection. 

When handling all hormones including the CIDR wear latex or non-latex gloves regardless if you are a man or a woman. Example, prostaglandin is a smooth muscle contractor, our intestines are the largest smooth muscle in the human body. If prostaglandin is absorbed through the skin it can “tie up” the digestive system. Additionally, the hormones function in the human body like it does in a heifer therefore, extreme care should be taken when handling all synchronization hormones.

Protocol Categories

Because there are several protocols for heifers, each protocol has been put into one of three categories:

  1. Heat Detection Protocol
  2. Heat Detection and Time AI Protocol
  3. Fixed Time AI Protocol

1. Heat Detection Protocols: Heifers in these protocols should be inseminated 6 to 12 hours after the first observation of standing heat. During peak heat activity which is approximately 48 to 72 hours after prostaglandin; heat detection should occur at a minimum of 3 times per day for at least 1 hour per check for a total of 3 hours with 5 to 6 hours of heat detection being better. The recommended heat detection protocols for heifer include:

  • 1 Shot PG (Prostaglandin)
  • 7 Day CIDR® - PG
  • MGA® - PG

2. Heat Detect and Time AI (TAI) Protocols: These protocols include a combination of both heat detection and timed insemination. Heifers observed in heat should be inseminated 6 to 12 hours after standing heat. After the PG injection heat detection occurs for approximately 3 days, all heifers not showing heat will be given an injection of GnRH and inseminated (i.e. timed insemination). The amount of time spent on heat detection is reduced and early responders have a better chance of conceiving compared to a single fixed-timed AI. The recommended Heat Detect and Time AI protocols include:

  • Select Synch + CIDR® & TAI
  • MGA® - PG & TAI
  • 14-day CIDR® - PG & TAI

3. Fixed-Time AI (TAI) Protocols: With a fixed-time protocol, all heifers are inseminated at a pre-determined time and no heat detection has to occur. In general heifer pregnancy rates for fixed-time AI protocols tend to be 5 to 10% lower than heat detection alone. When considering these protocols, synchronize no more females than can be inseminated in a 3 to 4 hour period of time. Recommended Fixed-Time AI protocols include:

  • 7-day CO-Synch + CIDR®
  • 5-day CO-Synch+ CIDR®
  • MGA® - PG
  • 14-day CIDR® - PG

More Information

Additional resources for a successful breeding season include:

For more information related to estrous synchronization, contact: