Estrus Synchronization Protocols for Holsteins: A Practical Comparison

Synchronization programs let a herd breed cows on a schedule instead of waiting to see them in heat. For Holsteins, whose heats can be short and subtle, that is a big advantage. But the acronyms pile up fast: Ovsynch, Presynch, Cosynch, Double Ovsynch, G6G, Resynch. This article lays out the main options in plain terms, what each is trying to accomplish, and the trade-offs that decide which one suits a particular herd. The specific drugs and exact schedules should always be set with your veterinarian, so here we focus on the logic and the timing patterns, not products or doses.

What these programs are trying to do

Every timed AI program is built from the same few ideas. Use GnRH to start a new follicular wave and, in many cases, ovulate or luteinize a follicle. Use prostaglandin (PGF) to dissolve the corpus luteum. Use a second GnRH to trigger a timed ovulation. Then inseminate at a fixed interval. The differences between protocols are mainly about how well they prepare the cow before that final sequence starts, because a cow that begins the program at the wrong stage of her cycle will respond less well.

The core programs

Ovsynch

The original three-injection program: GnRH, then PGF seven days later, then a second GnRH about 56 hours after the PGF, with insemination roughly 16 hours later, according to a University of Wisconsin extension presentation. A Progressive Dairy summary reported that about 90 percent of cows ovulate and that pregnancy per AI was comparable with cows bred after detected heat, with days open shortened by about one estrous cycle. Its weakness is that results depend on where the cow is in her cycle when the program begins.

Ovsynch56 and other timing variations

A common modification shortens the interval between PGF and the second GnRH to 48 hours, with insemination 24 hours after that. A student resource from the Dairy Challenge program lists both versions along with Cosynch72, in which the second GnRH and the insemination happen together after a longer 72-hour interval. Cosynch72 is easier on labor because there is one fewer handling, but the Stevenson paper from the Western Canadian Dairy Seminar reports lower pregnancy per AI for one Cosynch-72 trial than for Ovsynch-56 (29.0 versus 33.7 percent). One study should not decide your protocol, though; it shows a trade-off between convenience and results.

Presynch-Ovsynch

Presynchronization tries to put cows at a more favorable stage of the cycle before Ovsynch starts. The classic version uses two PGF injections 14 days apart, followed by Ovsynch about 12 days later. The Stevenson paper reports that Presynch-Ovsynch gave cows about 42 percent greater odds of pregnancy than timed AI without presynchronization, and that adding GnRH to the presynchronization step raised the odds further. The cost is more injections, more handling days and a longer wait before the first AI.

Double Ovsynch

This program runs a full GnRH-PGF-GnRH sequence first, then starts a standard Ovsynch with the aim of getting nearly every cow to start the real program in the best possible hormonal state. The Dairy Challenge resource describes it as GnRH, seven days to PGF, three days to GnRH, seven days to Ovsynch56. Stevenson cites a 2017 meta-analysis that found Double Ovsynch improved pregnancy per AI over Presynch-Ovsynch in first-lactation cows but not in older cows. It also involves the most injections and the highest cost.

Side-by-side comparison

Program	Core idea	Handling workload	Main trade-off
Ovsynch	GnRH, PGF, GnRH, timed AI	Low	Results depend on starting cycle stage
Cosynch72	Second GnRH given with AI	Lower still	Convenience may cost some pregnancy per AI
Presynch-Ovsynch	Two PGF before Ovsynch	Moderate	Longer wait for first AI, more handling
Double Ovsynch	Full Ovsynch before the real Ovsynch	High	Most injections, may help first-lactation cows most
Heat detection with PGF	PGF then breed observed heats	Moderate	Depends on detection quality

Resynchronization: do not forget the open cows

First service is only half the story. A cow that fails to conceive should be rebred promptly. The Wisconsin presentation describes three approaches: start the resynchronization after a pregnancy check; start it before the check so that the second round is ready to go if the cow is open; or combine detection of returning heats with PGF at the check. The Stevenson paper notes that giving GnRH before the Resynch-Ovsynch started raised pregnancy per AI from 29.0 to 33.5 percent in one trial, and that in a control resynchronization group cows bred on detected estrus had higher pregnancy per AI than timed-AI cows (39.1 versus 25.4 percent). That does not mean heat detection always wins. It means timed AI programs rescue cows you would otherwise miss, while detected heats are good matches when your detection is accurate.

Compliance is the hidden variable

A protocol only works if cows get every shot at the right time. The Wisconsin presentation illustrates the arithmetic: at 95 percent compliance per injection, a three-shot program reaches about 86 percent of cows with all injections, a five-shot program about 77 percent, and a seven-shot program around 70 percent. At 90 percent per injection the figures fall to roughly 73 and 59 percent for three and five shots. More elaborate programs are more sensitive to missed handlings. If your crew is stretched, a simpler program done perfectly may beat a sophisticated program done carelessly.

How to choose

1. Assess your detection. If a large share of cows is missed, timed AI usually helps. See our guide to heat detection and the reasons it fails.
2. Count your labor honestly. Add up handlings per cow and how reliably they happen.
3. Look at your groups. First-lactation cows and older cows may respond differently.
4. Consider your economics. Hormones, labor and delay all cost money; our guide to the dairy enterprise budget helps put numbers on it.
5. Measure results. Track pregnancy rate (see pregnancy rate as the master metric), not just conception.
6. Involve your veterinarian. They know the products, regulations and your herd's history.

For more resources, visit the agriculture directory and farm.fm's dairy coverage. This site is independent of any breed association and is no substitute for veterinary advice.