Timing of Insemination for Dairy Cattle

Many reproductive management activities on dairy farms revolve around timing. Because of labor and animal handling factors, it may not always be feasible to inseminate at a precise time for optimal success rates when using heat detection-based strategies but, establishing a good 12- or 24-hour time window for insemination can still result in good conception rates, with average rates only slightly below the optimum. Timing can be more precise with timed artificial insemination (AI) and pregnancy rates can be improved with a good protocol, but labor and animal handling are still important factors to consider. Regardless of the approach, it is important to keep timing in mind while looking for opportunities to improve efficiency and its associated economic gains.

This article will explain some of the key physiological events that impact timing of insemination and strategies for getting the timing right.

What's Happening Inside

Ovulation is the key event. The timing of ovulation, which is the release of an oocyte (egg) from one of the two ovaries, dictates when everything else needs to happen for insemination to successfully result in a sustained pregnancy. Without ovulation, any other activity related to insemination will be fruitless.

One reason the timing of events is so critical is because the oocyte travels quickly from the ovulation site to the fertilization site in the oviduct, and the fertile lifespan of an oocyte is brief. Ovulated oocytes can remain fertilizable for ten to twenty hours, but with later fertilization comes an increased risk of embryonic loss. Oocytes expected to develop into normal, healthy embryos generally need to be fertilized within ten hours of ovulation. Viable sperm cells should be at the site of fertilization awaiting arrival of the freshly ovulated egg for this to happen.

Another reason timing is important is because sperm cells need to be in the female reproductive tract for six to eight hours before they are capable of fertilizing an oocyte. They, too, have a limited lifespan, though not as brief as that of oocytes. Although live sperm cells have been found in the female tract up to 48 hours after insemination, sperm viability usually lasts for about 18 to 24 hours.

When fertilization is achieved, the resulting embryo makes its way to the uterus within a few days and will hopefully reside there for the duration of a healthy pregnancy.

Heat Detection

Efficient reproductive management often starts with attentive heat (estrus) detection. Regardless of the reproductive management strategies employed in a particular dairy operation, heat activity provides useful information. In some management systems, all inseminations may be based entirely on observed heat activity. Technology tools may be used to help with detection of estrus, providing around the clock coverage, but they are not essential. Sometimes timed AI is used, which lessens dependence on heat detection, but even then, detection of heat activity has value. Heat activity may indicate cyclicity in fresh cows, it may help identify health disorders in some cows, or it may serve to help with more timely reinsemination of cows that did not become pregnant to the previous service.

Historically, and even still today, the onset of standing heat is the best indicator for determining the optimal time for AI. Secondary signs are helpful, but less reliable, especially in terms of timing. With more and more use of automated activity monitoring systems, elevated activity has also proven to also be a fairly reliable indicator, with systems typically designed to identify when a certain threshold has been passed that exceeds normal activity for a particular cow. Whether relying on the onset of standing estrus or increased activity, aiming to perform AI within a certain time window after these events should be the goal, unless the plan is to use timed AI exclusively.

Getting the Timing Right

Ovulation occurs, on average, 28 hours after the onset of standing heat. In general, AI should be performed sometime between the onset of heat activity and time of ovulation. Narrowing the window and getting the timing more precise can oftentimes increase the odds for pregnancy success, but it also needs to be balanced with other management priorities.

The AM-PM rule was developed several decades ago as a guide for timing of AI. Cows first seen in standing heat in the morning are inseminated in the afternoon, and those observed standing later in the afternoon or evening are bred the following morning. Though using the AM-PM rule is still a viable approach, there are some inherent challenges. For one, it relies on a practice of frequent observation throughout the day. Secondly, the frequency of observable estrous behavior can be impacted by a variety of herd and facility conditions, and it will never be 100% reliable. It may not be the most feasible for most herds.

If heat detection is not diligently performed multiple times each day, it is often best to inseminate within six hours after they are first detected in standing heat. Waiting ten or twelve hours may result in cows being bred too late. Breeding within a few hours of first detection is commonly done in herds; it may be that someone walks through all eligible cows once each day, and this is enough to achieve reasonable success. It is not absolutely necessary to inseminate more than once a day, especially when the onset of estrus is not known.

Summarizing results from a large number of research studies, the optimal time for AI is 12 to 24 hours before ovulation, which correlates to 4 to 16 hours after the onset of standing estrus. This timing allows sperm cells to migrate and be prepared for fertilization, meeting a freshly ovulated oocyte at the right place and at the right time. If too early, sperm cells are less likely to be viable and at the site of fertilization when the oocyte is ready. If too late, it has been shown through several research studies that fertilization rates might still be high, but quality has been compromised and there is an increased risk for early embryonic loss.

Early insemination

• risk of reduced sperm viability for fertilization
• good quality embryos

Timely insemination

• best odds for long-lasting pregnancies

Late insemination

• high fertilization
• high embryonic death due to reduced oocyte quality before fertilization

Very early / very late insemination

• low fertility

Activity Monitoring Systems

Interestingly, the average interval to ovulation from the onset of standing estrus closely matches the interval from when an activity threshold is exceeded as detected by an automated activity monitoring system or the interval from gonadotropin-releasing hormone (GnRH) treatment. It is safe to expect all of these intervals to ovulation to be in the 24- to 32-hour range, averaging about 28 hours.

Activity systems monitor activity around the clock. Though they only capture what is typically considered to be a secondary sign of estrus (increased activity, not actual standing estrus events), researchers have demonstrated that it can still be used for determining an appropriate time for AI. There is little adjustment needed from traditional heat detection practices. However, it does take time to define each cow’s threshold, and there are differences between systems and how they are set up.

The increased awareness of animal activity allows for more precise timing of AI, if desired. Using a similar approach as the AM-PM rule, one can wait 4 to 16 hours after a cow surpasses the threshold for increased activity before AI, aiming for the optimal time window.

Timed AI

Timed AI lessens the need for heat detection but requires labor and supplies for management of synchronization treatments. Some of the most convenient protocols are designed with the final GnRH treatment and AI performed at the same time (e.g., Cosynch 72). While convenient, this approach will not lead to as high of conception rates as can be achieved with a slightly more complicated protocol that separates the final GnRH treatment from the time of AI. It has become standard practice in many herds to follow the Ovsynch 56 protocol, which calls for GnRH treatment 16 hours before AI, a more favorable time interval for maximizing conception rates. When presynchronization treatments are added with the more complex protocols, conception rates to timed AI oftentimes exceed what can be achieved with heat detection alone.

Claiming to follow an Ovsynch 56 protocol is not enough. Following through with every treatment (100% compliance) is critical. Though variability of an hour or two may not compromise the protocol too much, missing treatments on individual animals or delaying treatments for half of a day is a different matter. Accurate timing is essential for maximizing the odds of success – pregnancies.

Sexed semen

There is a common perception that inseminations with sexed semen are more fertile if pushed a few hours later than with conventional semen.

In one study (Bombardelli et al., 2016), insemination of lactating Jersey cows with sex-sorted semen closer to the time of expected ovulation (23-41 hours after the onset of estrus) yielded a higher conception rate than at earlier timepoints, and a similar benefit of later AI has been seen in heifers (Guner et al., 2020; Sá Filho et al., 2010). However, in another study using timed AI protocols, moving AI 6 hours later in the protocol did not result in conception rate improvement (Drake et al., 2020). These results suggest a benefit from delaying AI a few hours when using sexed semen after detection of estrus, but if using timed AI, stick with the protocol and do not delay insemination.

Putting it all Together

The scenarios presented below show how timing of insemination can be addressed with different reproductive management strategies. The shaded areas outline the times when insemination likely takes place under the different management systems. The size of the target window varies dramatically.

Scenario #1 – Heat detection & AI once a day

With once-a-day heat detection and AI, some cows will be inseminated at the time of optimum conception rates, but others inseminated at early or late time points will sacrifice a few percentage points. This approach may be efficient in terms of labor and result in acceptable conception rates, but early and late inseminations will have a negative effect on the overall average.

Scenario #2 – Heat detection & AI more than once a day

Following the AM-PM rule or using activity monitoring system can work well, with due diligence. Insemination of cows that have displayed reliable signs of estrus can be performed within a narrower timeframe when average conception rates are maximized.

Scenario #3 – Timed AI

Timed AI helps eliminate a lot of the guesswork; insemination can be performed at the optimal time for establishing new pregnancies – peak conception rate – though it is important to realize that if the timing is off, then the success rights will also likely be off.

In summary, the timing of insemination is an important factor in any dairy reproduction program. It will never be perfect, but the averages established through scientific research are helpful. Ideally, insemination will occur a few hours after the onset of estrus, the onset of elevated activity, or GnRH treatment. If in doubt, inseminate early rather than late, and hope the averages will work in your favor.

References:

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