Synchronization programs are always evolving, and you want to use the best one.
Kansas State University veterinarian Brad White says, “The problem is, the best has a couple of different definitions.”
In a recent episode of “Herd Health,” White and fellow K-State Veterinarian Bob Larson compare estrus synchronization protocols for heifers and cows, and how to determine which is best for your operation.
When determining what protocols to use for artificial insemination (AI), Larson explains there is a difference in steps for heifers versus cows. To see a list of protocols and steps, Larson recommends utilizing the Estrus Synch Planner on the Beef Reproduction Task Force website.
The Hormonal Toolkit: GnRH, Prostaglandin and Progesterone
Protocols are similar for cows and heifers, but there are a few differences to be aware of. Larson explains the three hormones used to synchronize estrus are progesterone, gonadotropin-releasing hormone (GNRH) and prostaglandin F2Alpha. What varies from cows to heifers is hormone placement time and combinations.
The period from giving the prostaglandin injection to optimal insemination time, is shorter in heifers than cows. When using fixed-time AI, cows should be serviced later.
Why Heifers Respond Faster Than Cows
Larson discusses a key difference in fixed-time AI with heifers is the length of protocol from start to finish. Some protocols can be as long 33 to 36 days or as short as eight days, so producers must decide how much time they have or are willing to spend.
Another factor to consider is how many times a producer will run animals through the chute. In some cases, it could be twice, once for a prostaglandin injection and once for insemination, and other cases could be up to four times. Group size and animal location are both items to consider when choosing the best protocol.
When looking at specific components like progesterone, different protocols list giving this for five, seven or 14 days. If heifers have not already reached puberty and are cycling, they will be jumpstarted, Larson says.
He explains some will reach puberty sooner than usual with this progesterone addition. The longer they’re exposed, the more successful jumpstarting will be. The downside is it is a longer process.
MGA vs. CIDR: Weighing Cost Against Convenience
Heifers can receive progesterone needed for estrus synch in feed form with melengestrol acetate (MGA) or intravaginally with a CIDR that slowly releases progesterone into the bloodstream.
MGA is inexpensive and you don’t need to run heifers through a chute, so if cost and gathering are concerns, this is an effective system. The disadvantage is that the dosage is 0.5 mg per head per day, and that can be difficult to maintain when factors like weather and herd dominance come into play.
To ensure the most successful synchronization, Larson stresses maintaining feeding schedules and allowing plenty of bunk space is crucial. If using MGA, the feeding period is usually 14 days.
White explains the decision to use MGA or CIDRs as cost versus convenience. However, MGA can only be used with heifers.
Most protocols include a GnRH injection at the time of fixed-time AI. This is because all protocols are designed to be optimized, meaning for the majority of the heifers, Larson says.
For example, a 66-hour time frame from the prostaglandin injection to insemination is best for most heifers. This could be late or early for some, so the GnRH injection causes heifers to ovulate if they haven’t already, but most protocols state that heifers will have ovulated prior to the time of insemination.
Some sources say to provide GnRH seven days prior to removing the progesterone source. Larson reminds producers that the whole point of these protocols is synchronization. Giving this injection at that time ensures heifers’ follicular waves are in the same pattern, meaning synchronization is tightened among the group.
The Postpartum Countdown: When to Start Synchronization
The main difference in synchronization in cows is timing between hormone administration and breeding. However, Larson also points out that cows do make the process a little more difficult when they have calves at their side or they are on pasture.
Cows are also actively calving, and Larson says they should calve at least 40 to 50 days before the start of synchronization, but they will vastly range.
Crunching the Numbers: Is AI Right for Your Operation?
Ultimately, deciding to use estrus synchronization and AI comes down to what works best for your operation.
“You have to do the math to make sure it’s worth it for you,” White says.
There are some differences when comparing the protocols for a seedstock and commercial operation.
Once you find a protocol that works for you, he adds, “There are some real advantages to picking a protocol, working with it, and going through the process.”
Consulting the Beef Reproduction Task Force, veterinarians, semen dealers and other community resources are great options when deciding what to implement in your operation.
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