At the 2018 Dairy Cattle Reproduction Council annual meeting, Paul Fricke, University of Wisconsin – Madison professor of dairy science and extension specialist in dairy cattle reproduction, reviewed the progression of timed-artificial insemination (A.I.) programs, discussed current recommendations and explained that timed-A.I. programs will continue to evolve.

The dairy industry offers a variety of reproductive management programs, including some that synchronize estrus via hormone protocols. “Many strategies can be implemented to achieve excellent 21-day pregnancy rates by increasing the A.I. service rate alone,” Fricke said. “Newer fertility programs increase both service rate and pregnancies per A.I. (P/A.I.).” With multiple programs available, Fricke said it’s important to implement a plan to submit cows for first A.I. and identify nonpregnant cows and return them to A.I. service to maximize the 21-day pregnancy rate.

A.I. to a detected estrus remains the cornerstone of most dairies’ reproductive management programs. However, submitting lactating dairy cows for first A.I. based on estrous detection alone will yield poor reproductive performance.

Heat detection hurdles

The first primary hurdle involves humans’ inability to visually detect estrus. Fortunately, current technologies (e.g., pressure-activated heat mount devices, tail chalking and activity monitoring systems) help overcome this challenge.

The second hurdle involves high-producing cows’ biology. With high-producing cows, estrous duration is often shorter; ovulation may not occur after expressing estrus, ovulation may occur without accompanying estrous behavior and some cows are anovular.

In 1995 when Ovsynch was introduced, dairy producers could increase their cows’ service rate. The original Ovsynch called for three sequential hormonal treatments to control ovarian function. In the first Ovsynch field trial, which used only timed A.I. without estrous detection, days to first A.I. and days open dropped. However, P/A.I. remained the same. Researchers concluded that estrous detection should be combined with Ovsynch and timed A.I. to boost reproductive performance.

When evaluating Ovsynch performance, researchers discovered that starting the Ovsynch protocol between days five and 12 resulted in more P/A.I. compared with starting it earlier or later during the estrous cycle.

Presynchronization boosts repro performance

Researchers took this discovery and evaluated presynchronization protocols to improve the success of estrous synchronization. The first presynchronization strategy tested used two prostaglandin F2α (PGF2α) treatments administered 14 days apart with the second PGF2α treatment preceding the first gonadotropin-releasing hormone (GnRH) treatment of an Ovsynch protocol by 12 days. When only cycling cows were included in the statistical analysis, P/A.I. to timed A.I. increased from 29% for cows submitted to an Ovsynch protocol to 43% for cows submitted to a Presynch-Ovsynch protocol.

Decreasing the interval between the second PGF2α treatment of Presynch to initiation of Ovsynch from 14 to 11 days increased ovulatory response to the first GnRH treatment and increased P/AI by approximately 7 percentage points when all cows were submitted to timed A.I. “If you use a Presynch-Ovsynch protocol for 100 percent TAI (timed A.I.) for first service, use a 10- to 12-day interval between the second PGF2α treatment and starting Ovsynch,” said Fricke.

Newer presynchronization strategies that combine GnRH and PGF2α help increase P/AI to timed A.I. Cows that were presynchronized using a Double-Ovsynch protocol had more P/A.I. than cows submitted to just a Presynch-Ovsynch protocol (50% vs. 42%).

A.I. timing

Numerous studies have evaluated “best timing” of hormone treatments and/or A.I. breeding. In the first published experiment using Ovsynch to hormonally synchronize ovulation, lactating cows were submitted to timed A.I. approximately 24 hours after the protocol’s last GnRH treatment. All cows ovulated to the second GnRH (G2) by 24 to 32 hours after G2.

To assess the effect of A.I. timing relative to a synchronized ovulation, lactating dairy cows were bred at zero, eight, 16, 24 or 32 hours relative to G2. Overall, cows in the zero-, eight-, 16- and 24-hour treatments had more P/A.I. than cows in the 32-hour treatment.

Another A.I. timing trial compared Ovsynch 48 (timed A.I. occurred 48 hours after G2), Cosynch 72 (timed A.I. occurred 72 hours after G2) and Ovsynch 56 (timed A.I. occurred 16 hours after G2). Ovsynch 56 resulted in numerically (but not statistically) greater fertility than the other treatments. Data suggest optimal fertility should occur when cows are inseminated 15 to 24 hours before ovulation.

Most dairies using Ovsynch 56 administer G1, PGF2α and timed A.I. in the morning, whereas G2 is administered in the afternoon to achieve a 56-hour interval from the PGF2α treatment to G2, and a 16-hour interval from G2 to timed A.I. Admittedly, some dairy managers find it difficult to implement this protocol due to the inconvenience or inability to handle cows in the afternoon. Despite lower reproductive performance, some farms use Ovsynch 48 or Cosynch 72 for convenience. “Detection of estrus and A.I. between the PGF2α treatment and G2 of Cosynch 72 protocol may help mitigate the decreased fertility to TAI when using this protocol variation,” Fricke said.

The last option is known as five-day Cosynch. This presynchronization protocol decreases the interval between G2 and PGF2α from seven days to five days. “The five-day Cosynch protocol is a good option for dairies that want to administer all protocol treatments and TAI in the morning, thereby simplifying implementation of this protocol,” said Fricke. “In addition, the five-day protocol allows for nonpregnancy diagnoses on Wednesday and Thursday, so cows diagnosed not pregnant can be reinseminated on the following Thursday or Friday.”

New twist: Second PGF2α treatment

A recent Ovsynch protocol change involves giving a second PGF2α treatment 24 hours after the first. “Including a second PGF2α treatment is absolutely necessary for the five-day Cosynch protocol because when a new, younger corpus luteum (CL) forms after G1 and is present at the PGF2α treatment, it will fail to regress after a single PGF2α treatment,” said Fricke. “Adding a second PGF2α treatment is highly recommended for all seven-day protocols, particularly when used for first TAI after a presynchronization strategy that incorporates both GnRH and PGF2α.”

Lack of complete luteal regression, particularly for multiparous cows, was the limiting fertility factor to timed A.I. Fricke reported that submitting lactating Holstein cows to a Double-Ovsynch protocol and timed A.I. for first insemination increased the percentage of cows inseminated by seven days after the end of the voluntary waiting period. Plus, this protocol increased P/A.I. at 33 and 63 days after first insemination – resulting in 64% and 58% more pregnant cows, respectively, than submission of cows for first A.I. after detection of estrus at a similar range of days in milk.

Resynchronization options

“A Resynch strategy is critical for achieving high 21-day pregnancy rates,” said Fricke. Three basic strategies exist. The first requires pregnancy diagnosis before starting the Resynch protocol, whereas the second calls for administering the first GnRH treatment seven days before pregnancy diagnosis.

There are pros and cons to these first two options. The advantage of delaying G1 until the pregnancy diagnosis is that more time is allowed for cows to show estrus for submission to A.I., thereby decreasing the total number of cows submitted to a Resynch protocol. This approach’s disadvantage is that resynchronization is delayed one week because nonpregnant cows must be identified before giving G1. “Overall, P/A.I. did not differ between cows submitted to a Resynch protocol 32 or 39 days after A.I.,” said Fricke.

The third Resynch strategy is based on decreasing the interval between A.I. services by increasing the A.I. service rate. Cows presynchronized with a single PGF2α treatment administered 12 days before G1 (resynchronization) had more P/A.I. than cows with high prostaglandin (greater than 1.0 ng/mL) at G1. When cows were presynchronized with either GnRH or PGF2α seven days before G1 of Resynch, more cows were inseminated to estrus when a PGF2α treatment was added. More cows completed Resynch when a GnRH treatment was added.

CL presence/absence indicates fertility

“Based on progesterone profiles at each treatment during the Ovsynch protocol, the best indicator of poor fertility to TAI is low progesterone [i.e., cows lacking a functional CL] at the PGF2α treatment of the Ovsynch protocol,” said Fricke. “Giving a second PGF2α treatment 24 hours after the first [in Resynch protocol] increases P/AI for cows initiating Resynch in a low-progesterone environment.”

One strategy to treat nonpregnant cows without a CL at G1 is to supplement with exogenous progesterone during Resynch. “Cows without a CL at G1 and treated with a CIDR (controlled internal drug release) for seven days had more P/A.I. at first and Resynch TAI,” Fricke said. “Many veterinarians now use the presence or absence of a CL at nonpregnancy diagnosis to implement a strategy to increase fertility to Resynch protocols or to increase the proportion of cows inseminated to a detected estrus after A.I.”

Development and optimization of fertility programs for first and Resynch timed-A.I. remains an active area of research that has advanced dramatically over the past 20 years and will most certainly change in the future.  

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