Gnrh Based System for Beef Cows
The Beef Reproduction Task Force, composed of representatives of the artificial insemination (AI) and pharmaceutical companies, veterinarians and university reproduction specialists, has developed recommended synchronization protocols for beef producers that will provide optimal pregnancy rates based on research and field use for both conventional and sexed (gender-selected) semen. The protocols can be found in genetic company catalogs and on the Beef Reproduction Task Force website.
Take note that not all protocols are for both cows and heifers. There is a difference in physiological response between heifers and cows; therefore, it is important to select the proper protocol. Likewise, follow the protocol as directed, giving the proper hormone injection or insert and breeding at the optimal insemination time. To help increase the success of the synchronization protocol, cows need to be at a body condition score of five or better during breeding season and be at least 50 days post-calving. If there are young, thin and/or late-calving cows in the herd, it is likely they are not cycling. The addition of a progestin, such as controlled-internal drug release (CIDR®) in the protocol can help jump start some of these non-cycling cows. However, caution needs to be taken, CIDR® or other progestins are not the "cure all" for thin, young and late-calving cows. An evaluation of the nutrition program is recommended if a high percentage of cows are not cycling.
Handling and Administering Synchronization Hormones
When handling all hormones, including CIDR®, wear latex or non-latex gloves regardless of if you are a man or a woman. For example, prostaglandin (PG) is a smooth muscle contractor, and 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 hormone functions in the human body like it does in a heifer or cow; therefore, extreme care should be taken when handling all synchronization hormones.
It is tempting to give a cow an injection in the rump, because there is the belief that cull cows solely end as hamburger beef. However, a majority of the "middle meats," such as ribeye rolls, short-loins, strip-loins, along with round are marketed as such. Therefore, Beef Quality Assurance guidelines should be followed when giving all injectable hormones. Secondly, giving the injection in the rump 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).
Cow Estrous Synchronization Protocols for Conventional Semen
The recommended cow estrous synchronization protocols for conventional semen have been put into one of three categories: 1) Heat Detection Protocol; 2) Heat Detection and Timed AI Protocol and 3) Fixed-Time AI Protocol.
Heat Detection Protocols
Cows in these protocols should be inseminated 12 hours after the first observation of standing heat. Peak heat activity occurs approximately 48 to 72 hours after prostaglandin. In order to optimize AI pregnancy rates, heat detection should occur at minimum three times per-day for at least one hour per-check. This equates to a total of three hours per-day heat checking with five-to-six hours of heat check increasing overall AI pregnancy rates. It is also important to train individuals to detect signs of heat (Table 1) and application of a heat detection aid will help assist in determining cows in heat when no one is watching. The heat detection protocols for cows include:
- Select Synch
- Select Synch + CIDR®
- PG Six-Day CIDR®
| Before Standing Heat (6-10 Hours before) | During Standing Heat (can last 6 – 24 hours) | After Standing Heat (up to 10 hours) |
| Will not stand to be ridden | Stands to be ridden | Will not stand to be ridden |
| Vocal and smells other cows | Nervous and restless | Clear mucous discharge |
| Nervous and restless | Congregates and rides other cows | |
| Attempts to ride other cows | Vulva moist, red and slightly swollen | |
| Vulva moist, red and slightly swollen | Clear mucous discharge | |
Heat Detect and Time AI (TAI) Protocols
These protocols include a combination of both heat detection and timed insemination. Cows observed in heat should be inseminated 12 hours after standing heat. After approximately three days of heat detection, all cows not showing heat after PG injection will be given an injection of gonadotropin-releasing hormone (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-time AI. The Heat Detect and Timed AI protocols include:
- Select Synch & TAI
- Select Synch + CIDR® & TAI
- PG Six-Day CIDR® & TAI
Fixed-Timed AI (TAI) Protocols
In a fixed-time AI protocol, all cows are inseminated at a pre-determined time with no heat detection required. These protocols are typically more intensive and expensive, but no time is dedicated to heat detection. However, expect a lower conception rate compared to the previous protocols and when considering these fixed-time AI protocols, only synchronize the number of cows that can be inseminated in a three-to-four hour period (protocol dependent). Fixed-Time AI protocols include:
- Seven-Day CO-Synch + CIDR®
- Five-Day CO-Synch + CIDR®
- PG Five-Day CO-Synch + CIDR® (For Bos Indicus cows only)
Cow Estrous Synchronization Protocols for Sexed Semen
A straw of sexed semen (gender selected), may have two-to-four million sperm cells compared to 20 to 40 million in a conventional straw that include both male and female sperm cells. Due to lower number of sperm cells per straw and other negative influences, different protocols were developed to improve conception rates to sexed semen.
The recommended heifer estrous synchronization protocols for sexed semen have been put into one of three categories: 1) Heat Detection Protocol; 2) Fixed-Time AI Protocol 3) Split-Time AI. Note there are both heifer and cow sexed-semen protocols; use the correct one.
Heat Detection
All cow heat detection protocols listed for conventional semen are acceptable to use with sexed semen. Estrous detection aids are highly encouraged. Note that females are artificially inseminated 16 to 22 hours after the first observation of standing heat with sexed semen compared to 12 hours with conventional semen.
Timed AI
To optimize pregnancy rate, it is recommended to use estrous detection aids and only use sexed semen on cows that have activated heat detection aids and the cows not detected in heat bred to conventional semen.
- Seven-Day CO-Synch + CIDR®
Split-Time AI (STAI)
Go to the Beef Reproduction Task Force website to review the split-time AI protocol. Additional time is required; however, number of cows detected in heat and bred at the optimal time will result, improving the chance of a higher conception rate.
- Seven-Day CO-Synch + CIDR® & STAI
Estrous Synchronization Planner
Using the Estrus Synchronization Planner can help you develop and compare synchronization protocols, as well as develop a synchronization and breeding calendar for both cows and heifers. The planner can found at the Iowa Beef Center website or Beef Reproduction Task Force website as a free download.
For more information related to estrous synchronization contact Robin Salverson, Olivia Amundson or Kiernan Brandt.
Source: https://extension.sdstate.edu/2021-beef-cow-synchronization-protocols
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