Everyone loves a good transformation story, and over the last two decades, reproductive management in the dairy industry has been one of the standout success narratives. The combination of timed AI programs, activity monitors and improved fertility protocols has pushed conception rates in lactating cows to heights that would have seemed impossible in the early 2000s.
While milking cows have been getting the spotlight, the animals waiting in the wings — nonlactating heifers — quietly carry enormous economic weight. These animals are the future herd, and every day they’re not pregnant, they’re eating money.
“What’s the biggest cost of raising heifers?” Paul Fricke, professor and Extension specialist at the University of Wisconsin-Madison, prompted to a captive audience at the Dairy Cattle Reproduction Council annual meeting.
“Feed costs,” he answered. “Raising heifers is all about days on feed. And what controls days on feed? When they calf. And what determines when they calf? When they get pregnant. Better reproduction in heifers is about decreasing total days on feed.”
The Gold Standard and Its Gaps
The 5-day CIDR-Synch protocol, involving two timed gonadotropin releasing-hormone (GnRH) injections and two timed prostaglandin (PGF) injections along with a progesterone-releasing insert, has been the go-to standard for years. It’s reliable, structured and widely adopted.
However, even the best protocol may not work for all cattle. In the case of heifers, two issues stand out:
- About 30% of heifers come into estrus a day early, which complicates timed AI plans.
- Only 25% to 40% ovulate following the first GnRH injection (G1).
These issues can be attributed to how heifers differ from lactating cows, reproductively speaking:
- They have more follicular waves, so they’re at more varied cycle stages when synchronization protocols begin.
- Their progesterone levels can be higher, which dampens the LH surge needed to trigger ovulation.
Researchers, including Fricke, decided to ask: Knowing what we know, can we do better with heifers?
Small Change, Big Consequences
After investigations into presynchronization with prostaglandin to prevent early estrus within the protocol and elimination of the CIDR device to increase ovulatory response to G1 didn’t deliver the desired results, Fricke has the idea of a 6-day CIDR-Synch protocol.
“Our idea here was that if we leave that insert in for an extra 24 hours, maybe we can suppress that early estrus and force the heifers to a timed AI,” Fricke explained.
They found that by leaving the CIDR in for an extra day, they eliminated the early estrus: None of the 6-day protocol heifers showed early estrus, while 28% of 5-day protocol heifers did.
This extra day of progesterone pushed out ovulation so that these animals didn’t come into heat. These animals were then bred with sexed semen, however, while the CIDR was left in for an extra day, the timing of insemination remained the same. This resulted in the heifers being bred too early relative to ovulation, as well as reduced conception rates.
When the team delayed AI by just eight hours for animals on a 6-day CIDR protocol, conception rates jumped back up.
“The timing of insemination is important for fertility, especially with sexed semen,” Fricke concluded. “I think [the 6-day CIDR] protocol is a good protocol. It eliminated the early estrus. It allows for 100% timed AI. It may be a little bit of a pain with that eight-hour interval, but I think it could be eight to 12 hours.”
Practical Takeaways
If implementing or recommending the 6-day CIDR-Synch protocol in heifers, key considerations are:
- The protocol reduces early estrus events, making grouped AI more manageable.
- Ovulation occurs later, so timed AI must be adjusted accordingly.
- Heifers respond more uniformly to the longer progesterone exposure, improving synchrony across the group.
Where We Go From Here
Dairy reproduction has evolved from managing the herd to managing physiology. This 6-day CIDR-Synch is a great example of this shift as a smarter application of the biology we already understand.
For heifers, whose reproductive rhythms differ from cows in subtle but important ways, this one-day adjustment offers a meaningful opportunity to boost performance without too much of a management burden.
