As any dairy farmer will tell you, one of the trickiest reproductive challenges in herd management is silent estrus. Unlike typical estrus, where cows show noticeable signs like restlessness, mounting behavior, or mucus discharge, silent estrus sneaks by almost undetected. That means you could have cows cycling perfectly well—but missing breeding opportunities simply because the signals are too subtle to notice.

Over the years, more and more producers and vets are turning to follicular monitoring using ultrasonography to fill in the gaps. Tracking follicle development offers a unique glimpse into a cow’s reproductive status—even when she’s not “acting in heat.” Understanding how follicles grow, ovulate, and sometimes regress without typical behavioral signs gives us a window into silent estrus that’s been missing for too long.

What Exactly Is Silent Estrus?

Silent estrus, also called subestrus, occurs when a cow experiences normal ovarian cycles and hormonal fluctuations but doesn’t display any obvious external signs of being in heat. This problem is more common than many think, especially in high-yielding dairy cows. Stress, metabolic demands from lactation, and even environmental factors like heat can all contribute to suppressed behavioral signs of estrus.

What’s frustrating is that these cows may be fully fertile. The ovaries are doing their job—growing dominant follicles, releasing hormones, even ovulating. But from a human perspective, nothing seems to be happening.

Why Follicle Monitoring Matters

That’s where tracking follicle development becomes a game changer. The growth and regression of ovarian follicles follow a predictable wave pattern, typically involving two or three waves during an estrous cycle. By using ultrasound to keep tabs on this process, we can:

• Detect when a dominant follicle is nearing ovulation

• Confirm if a cow has ovulated

• Observe if follicles are regressing abnormally

• Identify cystic structures or non-ovulatory follicles

Even without behavioral signs, the ovaries are “telling us” what’s going on. And when silent estrus is suspected, the presence of a mature dominant follicle or a newly formed corpus luteum is a strong indication that the cow is cycling normally beneath the radar.

How Ultrasound Tracks Follicle Development

A skilled technician or vet can visualize follicles as small as 2–3 mm using a rectal ultrasound probe. As follicles mature, they typically grow to 15–20 mm before ovulation. With real-time imaging, you can see:

• Number of follicles in each ovary

• Size and location of the dominant follicle

• Presence of multiple follicular waves in the cycle

• The transformation of a dominant follicle into a corpus luteum (CL)

This is particularly helpful around day 10 to 14 of the estrous cycle. If a CL is present and no signs of estrus were seen earlier, it’s a strong clue the cow went through silent estrus.

What makes this method even more valuable is the ability to repeat it every few days to monitor follicular dynamics over time. Unlike hormone assays, which offer only a snapshot, ultrasound gives a moving picture of the cow’s reproductive rhythm.

Silent Estrus and High-Production Dairy Cows

Research has shown that high-producing cows are more likely to experience silent estrus. Their bodies are so focused on converting energy into milk that reproductive behavior often takes a back seat. Hormonal profiles may be perfectly normal, but mounting activity, standing heat, and other signs can be diminished or absent.

Follicle tracking helps fill in these missing signals. In fact, studies in the U.S. and Europe show that combining timed artificial insemination (TAI) protocols with follicular monitoring improves conception rates in herds plagued by silent estrus. You don’t need to wait around hoping to catch behavioral heat—you can act based on actual ovarian status.

How I Use Follicular Monitoring on the Farm

On our dairy, we started using ultrasound regularly a few years ago. Initially, we just used it for pregnancy checks. But once we began tracking follicle growth as part of our heat detection protocol, everything changed.

For instance, we had a few cows that looked totally inactive—no signs of heat, no mounting behavior, nothing. But when we scanned them on days 8, 11, and 14 of the cycle, we saw clear follicular waves, with dominant follicles growing, regressing, and being replaced. A few even had clear CLs by day 16—meaning they had ovulated silently.

Now, if we suspect a cow is in silent heat, we do a quick scan. If we see a dominant follicle that’s 16 mm or more, we’ll plan a timed AI. We’ve had great success with this approach—much higher than simply relying on visual heat signs alone.

Follicle Development and Hormone Interplay

It’s impossible to talk about follicles without touching on the hormonal environment. The dominant follicle secretes estrogen, which normally triggers heat behavior. But when that behavioral response is muted—whether due to metabolic stress or other factors—we’re left with estrogen spikes that don’t result in any visible signs.

Meanwhile, the release of luteinizing hormone (LH) leads to ovulation, whether or not the cow displays standing heat. The newly formed CL then produces progesterone, which suppresses further heat signs until the next cycle.

By using ultrasound, we’re not guessing what’s happening hormonally—we’re seeing it in action. If there’s a CL, progesterone is high. If a big follicle is present with no CL, ovulation is probably near. This kind of information is golden when you’re managing dozens or hundreds of animals.

Benefits Beyond Estrus Detection

Monitoring follicle development also has benefits beyond silent estrus:

• Cyst detection: You can distinguish between follicular and luteal cysts with ultrasound.

• Cycle staging: Know exactly where a cow is in her cycle to optimize AI timing.

• Postpartum recovery: Check whether the ovaries are resuming normal cycling after calving.

• Reproductive troubleshooting: If a cow isn’t getting pregnant, ultrasound helps narrow down the problem.

It’s not just about seeing follicles—it’s about interpreting what they mean in the broader reproductive picture.

When to Use Follicular Ultrasound

Timing is key. Here are a few situations where I’ve found it especially helpful:

• Day 7–10 postpartum: Check for early signs of follicular activity

• Day 14–17 post-insemination: Look for CL development, which suggests successful ovulation

• No heat signs 21+ days after breeding: Check for new follicular waves or CL regression

• Repeat breeders: Use sequential scans to identify timing mismatches or non-ovulatory cycles

The more familiar you become with your herd’s reproductive rhythms, the easier it is to spot problems and act quickly.

Closing Thoughts

Silent estrus is a frustrating but solvable challenge. By focusing on follicle development through ultrasound, you can take much of the guesswork out of heat detection. It gives you real data, not just observations, and allows for more timely and targeted insemination.

Whether you're running a small dairy or managing a large commercial herd, this tool offers a huge boost to your reproductive efficiency. We’ve seen better pregnancy rates, shorter calving intervals, and fewer open cows since making follicle tracking part of our routine.

Reproduction isn’t always loud—but if you listen closely, and use the right tools, your cows will tell you everything you need to know.