Category: Progesterone Testing

Why your analyzer’s chart differs

Thresholds belong to the assay; day counts travel.

Why test kits are not interchangeable

Not sure whether a box is the right one? Call 1 (866) 375-4357 or email vethelp@wondfousa.com with the lot number, Mon–Fri 9:00 AM – 6:00 PM PT.

Product specifications and equipment requirements cited here are those published by the manufacturer at the time of writing; always confirm against the manual and the insert supplied with your kit. This article is educational and is not a substitute for veterinary advice. Threshold values are assay-dependent and are not interchangeable between analyzers. Breeding decisions and result interpretation should be made in consultation with your veterinarian.

August 25, 2026

What You Need Before Your First Progesterone Test

The analyzer arrives, the kits arrive, and the first cycle is already underway. Then the instructions ask for a calibrated pipette and a centrifuge — neither of which is in the box. This is the most common reason a new analyzer sits unused through a heat it was bought to time.

The analyzer is one piece of a short workflow. Two or three inexpensive items complete it, and they are worth ordering at the same time as the instrument rather than after the first failed attempt.

Key takeaways

A calibrated 20–200 µL pipette is required equipment, not an accessory. The sample volume is too small to estimate.
A micro centrifuge is required for the serum workflow and not needed for the whole-blood workflow. Which kit you buy decides whether you need one.
A vortex mixer is listed as required equipment, though the buffer tube itself is mixed by inversion, not by shaking.
Blood collection supplies — needles, syringes, the correct tubes — are separate again, and are the item most often forgotten.

What ships, and what does not

A typical analyzer bundle contains the instrument, a starter pack of test kits, a tri-level quality control set, the manual and the warranty documentation. That is enough to understand the machine. It is not enough to run a sample.

Item	Needed for	What happens without it
Calibrated pipette, 20–200 µL	Every test, both workflows	The volume transferred is wrong, so the concentration reported is wrong. The result still looks like a normal number.
Micro centrifuge	Serum workflow only	No serum to test. The sample cannot be run at all.
Vortex mixer	Sample handling	Inconsistent mixing between runs, which shows up as scatter in a serial curve.
Pipette tips	Every test	Carryover between samples. Tips are single-use.
Collection tubes and needles	Every draw	No sample. The wrong tube type can also make a sample unusable.

The pipette is the part people underestimate

The sample volume for the canine progesterone test is measured in tens of microlitres. At that scale there is no version of “about right”. A transfer that is ten per cent short does not produce an error message; it produces a number that is ten per cent off, on a scale where a few nanograms per millilitre decide which day you breed.

Three habits matter more than the brand of pipette:

One tip, one sample. Tips are consumable for a reason.
Watch for the air gap. A bubble drawn into the tip is volume you did not transfer.
Keep the pipette vertical when aspirating and let it settle before dispensing. Liquid held on the outside of the tip is volume you did not measure.

Serum or whole blood decides your equipment list

The whole-blood kit removes the centrifuge from the workflow: the sample goes straight into the buffer tube. That is fewer steps and fewer opportunities for error, and for a small programme it can be the difference between testing daily and testing when convenient.

The serum workflow requires the spin, and it requires the serum to be clear. A pink or red tinge is haemolysis, and a haemolysed sample should be redrawn rather than run. We cover why in why two progesterone results disagree.

A checklist for the first week

Analyzer, on a level surface, away from direct sun and draughts
Test kits matching your chosen workflow — serum or whole blood
Calibrated 20–200 µL pipette and a supply of tips
Micro centrifuge, if you are running serum
Vortex mixer
Collection tubes, needles and syringes
The tri-level quality control set that shipped with the instrument — run it once before the first real sample, so you know what normal looks like

Ordering the whole list at once costs very little and removes the most common reason a new analyzer misses its first cycle.

Frequently asked questions

Do I need a centrifuge to run canine progesterone tests?

Only for the serum or plasma workflow, where the sample has to be spun before it can be pipetted. The whole-blood kit skips that step entirely — the sample goes straight into the buffer tube — so which kit you choose decides whether a centrifuge is on your list.

What size pipette do I need?

A calibrated adjustable pipette covering the 20 to 200 microlitre range, plus a supply of single-use tips. The test volume is measured in tens of microlitres, and at that scale there is no version of “about right”: a transfer ten per cent short returns a number ten per cent off, with no error message.

Can I use a syringe or a dropper instead of a pipette?

No. Neither delivers a repeatable volume at microlitre scale, and repeatability is the whole point — ovulation timing is read from the shape of a series, so scatter introduced by inconsistent transfers looks exactly like a biological change.

What should I run before the first real sample?

The tri-level quality control set that ships with the instrument. Running it once, before a bitch is in season, tells you what a normal reading looks like on your analyzer and confirms the pipetting technique before a result matters.

Sources

Wondfo USA. PETlife Pro-DX Immunofluorescence Analyzer, published test menu specifications and operating manual.

PETlife canine progesterone (cProg) test kit package inserts, whole blood and serum or plasma versions.

Keep reading

The calibration lives in the kit, not the analyzer.

Units, sample handling, and platform bias.

Why two results disagree

Setting up and not sure what you have? Call 1 (866) 375-4357 or email vethelp@wondfousa.com, Mon–Fri 9:00 AM – 6:00 PM PT.

August 25, 2026

Matching Insemination Method to the Progesterone Window

The fertile window does not move to fit your breeding method. The method has to fit the window. Progesterone timing tells you where that window is — but how much room you have inside it depends almost entirely on the semen you are breeding with. Fresh, chilled and frozen are three different problems, and the difference between them is measured in hours.

This is the practical payoff of getting Day 0 right. If you have read what the numbers actually mean, you already know progesterone predicts ovulation rather than confirming it. Here we take the next step: once you know when the eggs will be ready, which insemination method can actually reach them, and how tightly it has to be timed.

Key takeaways

Every method aims at the same target — days 4 to 6 after the LH surge. What changes is the margin around it.
Fresh semen forgives. Sperm can survive several days in the tract, so breeding a little early still works.
Chilled semen asks for precision and frozen semen demands it — roughly 12 to 24 hours of useful life after thawing, usually placed intrauterine and usually one attempt.
Timing protects the litter a bitch was already capable of. It does not increase the number of eggs she ovulated.

If you run a Finecare Vet or Pro-DX

The figures above come from laboratory and reference-method literature. This analyzer reads on its own scale and sits systematically higher: independent testing puts the regression at Finecare = 5.87 + 1.28 × reference, so on the Finecare chart estimated ovulation falls at 8–15 ng/mL and the fertile range at 15–40 ng/mL. Time from the chart supplied with your kit lot, not from the numbers in this article. Why thresholds belong to the assay that produced them →

The window everyone is aiming at

Canine breeding timing is counted from the LH surge, not from a raw progesterone number — because the day count is what transfers between analyzers, while the concentration thresholds do not. A widely used sequence looks like this:

Counting from the LH surge

Day 0 — LH surge. Progesterone is typically passing through roughly 2 ng/mL on many analyzers, though the exact number is assay-specific.
Day 2 — ovulation. The follicles release eggs that are not yet fertilizable.
Days 4–6 — the fertile window. The eggs finish maturing about two days after ovulation and remain viable for roughly two days after that. This is the target.

These are commonly reported averages, not guarantees. Individual bitches vary, and the numeric thresholds depend on the platform — which is exactly why one analyzer’s chart does not match another’s.

Every method below aims at the same Days 4–6 target. What changes is how wide a margin the semen gives you around it.

Fresh semen and natural mating: the widest margin

Fresh semen — whether delivered by natural mating or a same-room artificial insemination — is the most forgiving. Healthy fresh sperm can survive several days in the female reproductive tract, so it can be waiting when the eggs mature. In practice this means you can breed a little earlier and let the sperm meet the eggs, and a second mating a day or two later widens the coverage further.

Forgiving is not the same as careless. Sperm longevity depends on the quality of the male and the female’s tract; it is an average that individual pairs can fall short of. Timing still improves the odds, but fresh semen is where a rough estimate is most likely to survive being slightly off.

Chilled (cooled-shipped) semen: a tighter target

Cooling extends semen life long enough to ship overnight, but the trade-off is a shorter useful lifespan once it arrives — often on the order of a day or two of good motility rather than several. That removes most of the “breed early and wait” margin. Chilled semen is usually placed close to the fertile window itself, which means the shipment has to be timed to progesterone, not the other way around.

The logistics compound the biology: the stud owner has to collect, the courier has to deliver, and the eggs have to be ready — all within a window that is now measured in a couple of days. This is the first method where a send-out progesterone test with a slow turnaround starts to cost you options.

Frozen semen: the narrowest window of all

Frozen-thawed semen is the least forgiving material in dog breeding. Once thawed, sperm are typically viable for well under a day — often estimated at around 12 to 24 hours — and they do not travel well through the cervix. Two consequences follow.

First, timing has to land almost exactly on the mature-egg window; there is no reservoir of sperm waiting for the eggs to catch up. Second, the semen usually has to be deposited directly into the uterus — by transcervical insemination (TCI) with an endoscope, or by surgical insemination — rather than relying on natural cervical transit. Both are veterinary procedures, and both are typically single-shot: you generally get one well-placed insemination, so the progesterone timing that positions it has to be right.

The pattern: as semen lifespan drops from days (fresh) to hours (frozen), the margin for a timing error drops with it. The more you have invested in the semen — and frozen straws from a proven or deceased sire are often irreplaceable — the less room you have to be wrong about the window.

Method versus window, at a glance

Method	Usable lifespan	Timing margin	Typical placement
Fresh / natural	Several days	Widest — can breed early	Vaginal; repeat matings
Chilled	~1–2 days after arrival	Narrow — place near the window	Vaginal or intrauterine
Frozen	~12–24 hours post-thaw	Narrowest — near-exact	Intrauterine (TCI / surgical)

Lifespan figures are representative ranges from canine reproduction practice and vary with semen quality, handling and the individual bitch. Treat them as planning guides, not fixed values.

What timing does — and does not — do

It is worth being clear about the limit here, because it is easy to over-promise. Matching the method to the window improves the chance that the sperm and eggs actually meet while both are viable. When that happens, more of the eggs a bitch released can be fertilized, so a well-timed breeding tends to produce a litter closer to the top of that bitch’s own biological range.

What timing cannot do is manufacture puppies beyond the number of eggs she ovulated. Litter size is set mostly by genetics, age and ovulation rate — not by technique. Precise progesterone timing protects the litter a bitch was already capable of; it is not a lever for pushing her past it, and it is no substitute for breeding decisions made in her interest. The honest promise is fewer missed cycles and fewer wasted straws, not bigger litters on demand.

Where accuracy pays off most

Notice where the pressure concentrates. With fresh semen, a day’s error is often absorbed. With chilled and especially frozen semen, the same error can miss the window entirely — and those are the cases where the semen is most expensive, most limited, or impossible to replace.

That is why ovulation timing is really a sampling-frequency problem, not just an accuracy one. The decisions that matter depend on catching the rise as it happens and confirming it the next day, which is difficult when results take a day or more to come back. An in-house quantitative canine test — such as the cProg assay on the PETlife Pro-DX — exists to close that gap in exactly the frozen- and chilled-semen situations where a slow answer costs the breeding.

The takeaway

Pick the method, and you have picked how much margin you have. Fresh semen forgives; chilled semen asks for precision; frozen semen demands it. In every case the target is the same Days 4–6 window after the LH surge — and the tighter your semen’s tolerance, the more the whole breeding rests on getting the progesterone timing right. Plan the test schedule around the method you are actually using, not the other way around.

Frequently asked questions

How many days after the LH surge should I breed with fresh semen?

Days 4 and 6 after the LH surge is the sequence most commonly used, with the eggs fertilizable from roughly day 4 to day 6. Fresh semen survives several days in the female tract, so a mating placed slightly early is usually still in play when the eggs mature.

When is frozen semen inseminated?

Close to the middle of the fertile window, because thawed sperm are typically viable for well under a day and are normally deposited directly into the uterus rather than travelling through the cervix. Both transcervical and surgical insemination are veterinary procedures, and both are usually single-shot, so the day has to be right. Plan it with your veterinarian or a theriogenologist.

Does better progesterone timing produce a bigger litter?

No. Litter size is set mostly by genetics, age and ovulation rate. Good timing means more of the eggs a bitch actually released get fertilized, so a well-timed breeding tends to land nearer the top of her own range — it cannot push her past it.

Do I still need progesterone testing for a natural mating?

It is the case where you have the most margin, not the case where timing stops mattering. Repeat matings across days 4 to 6 cover a lot of error. Testing is what tells you which days those are, and it is what turns a missed cycle into information you can use next season.

Sources

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Wondfo USA. PETlife Pro-DX Immunofluorescence Analyzer, published test menu specifications.

Semen lifespan and placement figures are representative ranges from canine reproduction practice and vary with semen quality, handling and the individual bitch.

Keep reading

Building a testing schedule

When to draw the baseline and how fast to tighten the interval.

Why your analyzer’s chart differs

Thresholds belong to the assay; day counts travel.

This article is educational and is not a substitute for veterinary advice. Transcervical and surgical insemination are veterinary procedures. Threshold values are assay-dependent and are not interchangeable between analyzers. Breeding method, timing and any intervention should be decided with your veterinarian or a board-certified theriogenologist, and in the interest of the health of the dam and litter.

August 25, 2026

Timing an Elective C-Section With Progesterone: What the Data Supports, and What It Doesn’t
In breeds where an elective cesarean is routine, the hardest question is not whether to operate. It is when. Go too early and you deliver puppies that were not ready. Wait too long and you risk being overtaken by labour, or by a complication in the middle of the night.

Progesterone C-section timing is the most objective approach available for that decision, and the numbers behind it are genuinely good. They are also more limited than the confident charts circulating online suggest. This article covers both halves honestly, because the second half is the part that gets left out.

Read this before the numbers

De Cramer and Nöthling, whose 2018 Theriogenology study established the thresholds below, state in that same paper that controlled studies large enough to be convincing are still required before it can be considered safe to routinely perform a cesarean section once progesterone falls below a defined threshold. Nothing on this page is a surgical decision rule. Scheduling a cesarean is a veterinary decision that weighs the dam, the litter, the breed, the history, and the clinical picture — with progesterone as one input among several.
Key takeaways
- Progesterone 5 ng/mL or above means under a 2% chance of spontaneous whelping in the next 12 hours — useful for ruling a night out.
- Below 2.8 ng/mL, 99% whelp within 48 hours. Below 1.0 ng/mL, 100% do.
- The LH surge is the best gestational anchor at about 65 days, but prediction is only within ±1 day about 67% of the time.
- The evidence supports progesterone as an input, not as a standalone trigger for surgery.
If you run a Finecare Vet or Pro-DX
The figures above come from laboratory and reference-method literature. This analyzer reads on its own scale and sits systematically higher: independent testing puts the regression at Finecare = 5.87 + 1.28 × reference, so on the Finecare chart estimated ovulation falls at 8–15 ng/mL and the fertile range at 15–40 ng/mL. Time from the chart supplied with your kit lot, not from the numbers in this article. Why thresholds belong to the assay that produced them →

Why the calendar alone is not enough

Start with what a date can and cannot give you. De Cramer puts the gestational anchors as follows: measured from the LH surge, gestation runs about 65 days; from ovulation, about 63; from fertilization, about 61 — with the latter two explicitly less accurate than the first. Measured from the breeding date it spans roughly 58 to 68 days, which is far too wide to schedule surgery against.

Even the best anchor is a window rather than a point. Kutzler and colleagues, writing in Theriogenology in 2003, measured how precisely the date of the initial preovulatory progesterone rise predicts parturition:

67%

land within ±1 day

90%

land within ±2 days

100%

land within ±3 days

That is genuinely useful for planning. It is not precise enough, on its own, to pick an operating slot. A one-in-three chance of being off by more than 24 hours is exactly the margin that catches breeders who booked travel for the calculated date.

The calendar tells you which week. Progesterone tells you which day. Neither tells you the hour on its own.

What the prepartum numbers actually say

In dogs, labour is preceded by an abrupt collapse in progesterone as the corpora lutea break down. Because that drop is large and tightly coupled to labour onset, it can be read as a countdown in a way that is not possible in most other species.

Figure 1. Probabilities from De Cramer and Nöthling (2018). Note that these describe the likelihood of spontaneous whelping, which is a different question from whether it is safe to operate at a given value.

The most underrated row is the top one

Most attention goes to the low thresholds, but the 5 ng/mL line is arguably the more practical finding for a breeder. Fewer than 2% of pregnant bitches at that concentration enter spontaneous whelping within the following 12 hours, which places her at low risk of needing overnight observation.

Knowing a female is not going to whelp tonight is worth as much to an exhausted breeder in week nine as knowing that she is. It converts a fortnight of broken sleep into targeted vigilance.

Where the evidence stops

This is the section that most articles on progesterone C-section timing omit, and it matters more than any threshold.

The published probabilities describe when a bitch is likely to whelp on her own. They do not, by themselves, establish when it is safe to operate. Those are related questions, but they are not the same question, and the gap between them is exactly what the original authors flagged in the closing line of their own results.

Two practical consequences follow:
- A number is not a green light. A progesterone value below a threshold does not authorise surgery. It contributes evidence that the pregnancy has reached term and that luteolysis has begun.
- Assay differences compound the uncertainty. Thresholds in the literature were established on particular assays. Nöthling and De Cramer found chemiluminescence readings averaging only 85% of paired radioimmunoassay values on canine samples, with a 95% confidence interval spanning 58% to 112% — so a value of “1.9” on one instrument is not necessarily “1.9” on another. Serial testing on a single analyzer, showing the direction of travel, carries more information than one absolute number.
Do not manage this alone

If you are breeding a brachycephalic or otherwise high-risk breed, the planning conversation should begin weeks before the due window, not on the day a number crosses a line. Ask your veterinarian which anchor they want you to record, which analyzer they want results from, and at what point they want to be called.

How progesterone C-section timing works in practice

The workflow that gets the most out of progesterone in the final week looks roughly like this.
1. Record Day 0 during the heat cycle. Everything downstream depends on it. Count 65 days from the LH surge to define the expected window.
2. Agree the plan in advance. Discuss with your veterinarian when to start prepartum sampling, usually a few days before the calculated window opens.
3. Sample daily as the window approaches, on one analyzer, at a consistent time of day.
4. Watch the trajectory, not just the value. A fall from 12 to 6 to 3 over three days tells you more than a single reading of 3.
5. Combine with the other signals your veterinarian uses: rectal temperature, behaviour, and where relevant fetal monitoring.
Step 3 is the one that fails most often, and usually for logistical rather than clinical reasons. Daily sampling in the final week is impractical if every result means a clinic trip and a wait. As De Cramer notes, turnaround time is precisely what impedes the usefulness of commercial laboratory assays in cases where an immediate clinical decision is needed — which is the situation point-of-care progesterone was built for. The PETlife Pro-DX from Wondfo USA returns a quantitative canine progesterone (cProg) result from 75 µL of whole blood, serum or plasma in about 15 minutes, with no calibration step, so a daily reading is realistic rather than aspirational. Results can be exported over Wi-Fi, and logged against the individual dog in the free Pup Planner app so the falling curve is visible to whoever is making the call.

Whatever you use, the same discipline applies as during ovulation timing: one platform for the whole series, the analyzer recorded alongside every value, and interpretation against that instrument’s own reference range rather than a chart written for a different device.

Frequently asked questions

What progesterone level is used to schedule a C-section?
There is no single agreed number, and De Cramer and Nöthling explicitly note that larger controlled studies are still needed before routine threshold-triggered surgery can be called safe. In practice, veterinarians use the fall toward and below roughly 2 ng/mL as one signal that term has been reached, alongside gestational dating and clinical assessment.

Is progesterone better than temperature monitoring?
It measures the underlying event directly rather than a downstream consequence, and it is less easily confounded by ambient conditions, activity, or inconsistent technique. Most clinicians use both rather than choosing between them.

How early should prepartum testing start?
That depends on your gestational anchor and your veterinarian’s protocol. Because Kutzler and colleagues found prediction from the initial progesterone rise correct within ±1 day only about two thirds of the time, starting a few days before the calculated date is usually sensible.

Can I use a value from a different clinic’s analyzer?
It is best avoided. Progesterone platforms disagree systematically on the same sample, so mixing instruments in a prepartum series can create an apparent fall or rise that reflects the machine rather than the dog.

Sources

De Cramer KGM, Nöthling JO. The precision of predicting the time of onset of parturition in the bitch using the level of progesterone in plasma during the preparturient period. Theriogenology. 2018;107:211–218.

Kutzler MA, Mohammed HO, Lamb SV, Meyers-Wallen VN. Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration. Theriogenology. 2003;60(6):1187–1196.

Nöthling JO, De Cramer KGM. Comparison of progesterone assay by chemiluminescence or radioimmunoassay for clinical decision-making in canine reproduction.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Keep reading

Background

Due dates and whelping

Gestational anchors and what progesterone can’t confirm.

Important

Thresholds are analyzer-specific

Why a number from one machine isn’t the same on another.

Related

The false rise

Getting Day 0 right in the first place.

This article is educational and is not a substitute for veterinary advice. It does not provide a threshold at which surgery should be performed. Cesarean section is major surgery and the decision to schedule one, and its timing, must be made by a veterinarian who has examined the animal. Threshold values cited are assay-dependent and are not interchangeable between analyzers.
August 17, 2026

Why Your Analyzer’s Progesterone Chart Doesn’t Match the Textbook

You read that the fertile window starts around 8 to 10 ng/mL. Your analyzer’s chart says to breed at 15 to 35. Your friend’s vet quotes something else again. Everyone sounds confident, and the numbers do not agree.

They can all be right at the same time, because progesterone thresholds are analyzer-specific. Here is why — and, more usefully, which parts of a progesterone chart you can carry between instruments and which parts you absolutely cannot.

Key takeaways

Different assay technologies give systematically different numbers on the same sample. This is expected, not a defect.
Absolute values do not transfer between instruments. A threshold from one analyzer’s chart is meaningless on another.
Day counts do transfer. Breeding on days 4 and 6 after the LH surge is instrument-independent.
Use the reference range published for your analyzer, and stay on one platform for the whole cycle.

The same hormone, measured four different ways

Progesterone in canine serum is a single molecule with a single true concentration. What differs is how each instrument infers that concentration.

Detection principle	Typical platforms
Radioimmunoassay (RIA)	The historical reference method, now rare
Chemiluminescence (CLIA / ECLIA)	Reference-laboratory analyzers adapted from human clinical chemistry
Enzyme-linked fluorescence (ELFA) and fluorescence enzyme immunoassay (FEIA)	Benchtop laboratory analyzers
Fluorescence immunoassay, lateral flow (FIA)	Point-of-care veterinary analyzers, including the PETlife Pro-DX

Each of these uses different antibodies, different reagents, different calibration curves, and a different physical signal. The resulting disagreement has been measured directly. Comparing the Siemens Immulite chemiluminescence assay against the Coat-A-Count radioimmunoassay on paired samples from the same bitches, Nöthling and De Cramer found that Immulite values averaged just 85% of the RIA result, with a wide scatter around that mean (95% confidence interval 58% to 112%), and that 88% of Immulite readings were lower than their RIA counterparts.

A 15% average shift is not a rounding error in a range where the whole decision lives between 1 and 10 ng/mL. And the confidence interval is the more important number: on an individual sample the gap could be 42% low or 12% high.

Running the same progesterone sample on different systems produces different numbers. This is expected. The measurement methods and reagents are not the same, so the results are not the same.

This is why a manufacturer publishes a reference range tied to its own assay, and why textbook thresholds derived on a laboratory analyzer are not drop-in replacements for it. Validation studies are run per platform for the same reason: Milani and colleagues, writing in the Journal of Veterinary Diagnostic Investigation in 2022, had to establish the analytical performance of a fluorescence enzyme immunoassay specifically on canine serum before it could be used for ovulation timing, reporting intra-assay coefficients of variation of 2.6% to 5.2%. Good performance on one instrument says nothing about the numbers another instrument will report.

Progesterone thresholds don’t transfer; day counts do

The most useful mental model is to split a progesterone protocol into two layers and treat them completely differently.

Does NOT transfer

Absolute concentrations

Threshold values, breeding-window ranges, and any “breed at X ng/mL” rule. These belong to the assay that generated them. Borrowing one from another instrument is the fastest way to mistime a breeding.

Transfers freely

Day counts and cycle shape

Ovulation about 2 days after the LH surge. Eggs fertilizable about 2 days later. Breeding on days 4 and 6 after the surge for fresh semen, days 6 and 7 for frozen or chilled. Whelping about 65 days after the surge.

The right-hand column is anchored to events, not to numbers. That is what makes it portable. Once your analyzer has told you where Day 0 is on its own scale, the calendar takes over and the instrument stops mattering.

A worked example

Suppose you are running canine progesterone on a PETlife Pro-DX. The published specification for the cProg test gives a linear range of 1 to 50 ng/mL and a reference range of 15 to 35 ng/mL, on 75 µL of sample with results in about 15 minutes.

Meanwhile, the interpretation table in Kurt De Cramer’s widely used reference on simplifying the canine reproductive cycle — built on laboratory assay values — places the fertilizable period at 8 to 10 ng/mL and above. Those two statements look contradictory. They are not, because they are two different rulers describing the same event: the point in the cycle at which the oocytes have matured. Read each against its own scale and both point at the same days.

The error to avoid

Reading 9 ng/mL on a point-of-care analyzer, recalling that “8 to 10 means fertilizable” from an article written around a different platform, and breeding that afternoon. The number came from one ruler and the rule came from another. Check where you are on your analyzer’s chart, and cross-check it against the day count from Day 0.

What to do about it, practically

Find the reference range for your exact test and instrument. Not the analyzer brand in general, and not a chart someone posted for a different device. If it is not in the kit insert, ask the manufacturer.
Stay on one platform for the entire cycle. Since timing depends on detecting a rise, an assay that reads consistently is usable even if its absolute values differ from a reference laboratory. Mixing platforms mid-cycle destroys the trend.
Record the analyzer alongside every result. A value from two seasons ago is only comparable to today’s if you know it came from the same instrument.
Anchor on Day 0 and count days. This is the layer that survives any platform change.
Check the unit. ng/mL and nmol/L differ by a factor of about 3.18, and a number that looks post-ovulatory in one unit can be a just-surged value in the other.

For the Wondfo cProg test specifically, the published specifications and reference range are listed on the PETlife Pro-DX product page, and technical questions can go to the PETlife support team at vethelp@wondfousa.com or 1-866-375-HELP (4357). Asking the manufacturer for the range that matches your kit is a reasonable request, and a better source than a third-party chart.

The same four events on a miniVIDAS, an IDEXX chart, and the Pro-DX

Many reproduction clinics hand out a two-column card that lists miniVIDAS values next to IDEXX values, row by row, with the LH surge, ovulation, first breeding and the frozen-semen implant marked down the side. The best-known version comes from the International Canine Semen Bank in Colorado (ICSB-CO) and dates from 2004. Breeders who move to a PETlife Pro-DX often ask where its numbers would sit on that card. The table below answers that by anchoring all three columns to the same events rather than by converting any number.

Figure 1. The four events from the ICSB-CO comparison card, drawn where each analyzer reports them, with the Finecare Vet / Pro-DX timing chart on the third row. The horizontal scale is compressed so the 1 to 10 ng/mL region stays readable. *The Pro-DX LH-surge band is distributor guidance, not part of the manufacturer’s timing chart, which begins at 8 ng/mL. This figure shows that the scales differ; it is not a conversion chart.

Event on the cycle	miniVIDAS ICSB-CO chart, 2004	IDEXX ICSB-CO chart, 2004	PETlife Pro-DX ★ Finecare Vet / Pro-DX timing chart, 2025
LH surge, Day 0 “Looking for a significant rise”	≈ 2.0 band 1.5–3.5	≈ 1.5 band 1.5–2.5	≈ 2–4 distributor guidance; the timing chart itself starts at 8 and says “below 8, test again in 3 days”
Ovulation, Day 2 “Breed in 48 hours”	≈ 8.5 band 8.0–10.5	≈ 4.5 band 4.5–5.5	8–15 · “Estimated ovulation” test again the next day to confirm the jump; if still 8–15, she has not ovulated yet
First breeding, Days 4–6 “First breeding ideal”	≈ 17 band 15–20.5	≈ 9 band 8–11	15–40 · “Fertile range” AI or natural tie 1–3 days after ovulation; inseminate twice within the range
Frozen-semen implant, Days 6–7 “Surgical implant of frozen semen ideal, or last time to breed”	≈ 36.5 band 33–40	≈ 19.5 band 18–21.5	Still within 15–40 TCI or surgical 3–5 days after ovulation; the chart gives no separate value and warns that the chance of pregnancy falls after 4 days post-ovulation
Retest cadence	—	—	Below 8: retest in 3 days · 8–15: every 2 days · 15 and above: every day
What the chart is anchored to	The LH surge. Days are counted from the rise.		The ovulation date. The chart asks you to pin down ovulation with a next-day test, then count breeding days from there.

How to read this table

Read across a row, never down a column into another analyzer’s chart. The miniVIDAS and IDEXX columns are one clinic’s working card, compiled from its own paired results in 2004, and the “IDEXX” it refers to is the IDEXX reference-laboratory assay of that time, not the Catalyst One bench analyzer sold today. The spread between those two columns is wider than the published validation work would predict, which is a reminder that a clinic card is a practical tool, not a validation study.

The Pro-DX column is not derived from the other two. It is the manufacturer’s own timing chart, which is written around the ovulation date rather than the LH surge. That is why its “first breeding” and “frozen” rows share one range: on this chart the day count from ovulation does the work, and the number only confirms that she is still inside the fertile range. Follow the chart supplied with your kit lot, since the manufacturer notes the ranges can shift slightly between lots.

The practical translation for someone switching from a miniVIDAS card to a Pro-DX: the moment you would have circled on the card as “ovulation, breed in 48 hours” is the moment the Pro-DX reads 8 to 15 ng/mL and jumps clear of that band the next day. The “first breeding ideal” row on the card corresponds to the Pro-DX result entering the fertile range at 15, one to three days after that jump. And the “frozen implant” row is not a number on the Pro-DX at all. It is three to five days after the confirmed ovulation, with the result still inside 15 to 40.

Why point-of-care testing still wins on timing

A fair question follows from all of this: if reference-laboratory chemiluminescence correlates most closely with mass spectrometry, why not simply send everything out?

Because ovulation timing is not an accuracy problem. It is a sampling frequency problem. As De Cramer puts it, turnaround time impedes the usefulness of commercial laboratory assays precisely in the cases where an immediate clinical decision is needed — which is the reason point-of-care progesterone exists at all. The decisions that matter depend on catching a rise as it happens and confirming it the next day, and a highly accurate result that arrives 36 hours later can be worth less than a slightly different scale you can read this morning and again tomorrow.

What matters is not that two instruments produce identical absolute numbers, but that the one you use generates internally consistent, clinically interpretable results across the concentrations where the decisions live. That is a lower bar than laboratory equivalence, and a more relevant one.

One caution about semi-quantitative kits

Everything above assumes a quantitative result. Kits that report a band or a category rather than a number are a different proposition: De Cramer notes that semi-quantitative progesterone tests proved much less useful and reliable than quantitative assays returning an actual numerical value. They can answer “has anything started yet”, which is genuinely useful early in the cycle, but they cannot distinguish 2.2 from 3.4 ng/mL — and that distinction can move Day 0 by a full day.

Frequently asked questions

Why does my analyzer’s chart show higher numbers than the articles I read?

Because the chart is calibrated to that assay. Different detection principles and reagents produce systematically different values on the same sample — Nöthling and De Cramer measured chemiluminescence readings averaging 85% of radioimmunoassay values on paired canine samples. Both charts can be correct for their own instrument while disagreeing numerically.

Is there a conversion factor between analyzers?

Not one you should rely on. Published cross-platform conversion equations for canine progesterone are not generally available, and the relationship is not a simple constant: the 95% confidence interval in the Immulite-versus-RIA comparison spanned 58% to 112%. Stay on one instrument rather than trying to convert.

Which numbers from a breeding article can I actually use?

The day counts. Ovulation roughly 2 days after the LH surge, eggs fertilizable roughly 2 days after that, breeding on days 4 and 6 after the surge for fresh semen and days 6 and 7 for frozen or chilled, whelping about 65 days after the surge. These are anchored to events, not to a scale.

What is the reference range for the Wondfo cProg test?

The published linear range is 1 to 50 ng/mL and the listed reference range is 15 to 35 ng/mL, on 75 µL of sample with results in about 15 minutes. Confirm against the insert for your specific kit and version, since whole blood and serum or plasma kits are supplied separately.

My clinic gave me a miniVIDAS-versus-IDEXX card. Where does the Pro-DX sit on it?

Nowhere directly, because the Pro-DX chart is anchored to the ovulation date rather than to the LH surge. The event the card marks as “ovulation, breed in 48 hours” (about 8.5 on the miniVIDAS column, about 4.5 on the IDEXX column) is the Pro-DX “estimated ovulation” band of 8 to 15 ng/mL, confirmed by a jump the next day. The card’s “first breeding ideal” row corresponds to the Pro-DX result entering the 15 to 40 fertile range one to three days later, and the card’s frozen-semen row corresponds to three to five days after confirmed ovulation, not to a separate number. See the three-analyzer table above.

Sources

Nöthling JO, De Cramer KGM. Comparison of progesterone assay by chemiluminescence or radioimmunoassay for clinical decision-making in canine reproduction.

Milani C, Boscato EL, Gabai G, et al. Analytical and clinical performance of a fluorescence enzyme immunoassay for progesterone and determination of ovulation day in bitches. J Vet Diagn Invest. 2022.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Wondfo USA. PETlife Pro-DX Immunofluorescence Analyzer, published test menu specifications.

International Canine Semen Bank – Colorado (Brighton Animal Clinic). Progesterone value comparisons for ovulation timing: miniVIDAS and IDEXX. Clinic comparison chart, ICSB-CO 08/04.

MR Diagnostic Services / CanineP4. Finecare Vet & Pro-Dx Progesterone Timing Chart, 2025 update (FM01.30116.03). Estimated ovulation 8–15 ng/mL; fertile range 15–40 ng/mL; AI or natural tie 1–3 days and TCI or surgical 3–5 days after ovulation.

Keep reading

Units, sample handling, and platform bias.

Why two results disagree

Important

The false rise

Why one reading above 2 ng/mL isn’t Day 0.

Product specifications cited here are those published by the manufacturer at the time of writing; always confirm against the insert supplied with your kit. This article is educational and is not a substitute for veterinary advice. Breeding decisions and result interpretation should be made in consultation with your veterinarian.

Building a testing schedule

The False Rise: Why One Reading Above 2 ng/mL Isn’t Day 0

A bitch reads 2.6 ng/mL on day 6 of her heat. The breeder marks it as Day 0, counts forward, and books the stud for days 10 and 12. The breeding fails. Nothing was wrong with the dog, the semen, or the analyzer. The problem is that day 6 was never Day 0.

The false progesterone rise is the single most consequential misread in canine ovulation timing, and it is entirely avoidable once you know it exists.

Key takeaways

Some bitches show a spurious rise, sometimes as high as 2 to 3 ng/mL, during estrus, followed by several days back well below 2.
A single reading above 2 ng/mL is not Day 0. Day 0 is only confirmed by the next sample showing a continued rise.
The target is a sharp, continued rise to 6 ng/mL or above, not a single threshold crossing.
If progesterone falls back below 2, discard the anchor and keep testing.

If you run a Finecare Vet or Pro-DX

The laboratory-scale figures in this article come from reference-method literature. This analyzer reads on its own scale and sits systematically higher: independent testing puts the regression at Finecare = 5.87 + 1.28 × reference, so on the Finecare chart estimated ovulation falls at 8–15 ng/mL and the fertile range at 15–40 ng/mL. Time from the chart supplied with your kit lot, not from the numbers in this article. See how the common analyzers compare, and why thresholds belong to the assay that produced them →

What a false progesterone rise actually looks like

The phenomenon is described directly by Kurt De Cramer in his reference on simplifying the canine reproductive cycle. Clinical experience, he writes, shows that some bitches have a spurious rise of progesterone — sometimes as high as 2 to 3 ng/mL — that occurs during estrus and is followed by several days where progesterone remains well below 2 ng/mL. That spurious rise may then be followed by a second but true rise above 2 ng/mL, with an immediate and steep continued climb in the days thereafter.

He gives the failure mode explicitly: if a practitioner had noticed progesterone rising to, say, 2.6 ng/mL and had taken only a single blood sample, the timing would be incorrect.

Plotted, the trap is obvious. Sampled once, it is invisible.

Figure 1. Illustrative, based on the pattern described by De Cramer, with values on the reference laboratory (CLIA) scale. Both circles are readings above 2 ng/mL. Only the second one is Day 0. A breeder who anchored on day 6 would inseminate around days 10 to 12 — roughly five days before the eggs are fertilizable. On a Vcheck, Finecare/Pro-DX or other point-of-care analyzer the trap looks the same but sits at that machine’s own numbers — see how the common analyzers compare.

Why the cost of this error is so high

Anchoring on a false rise does not shift your timing by a few hours. It shifts it by the entire gap between the false and true rises, which in the example above is five days. Every downstream calculation inherits the error:

The breeding days are wrong, usually far too early
The stud is booked, shipped, or collected on the wrong dates
The predicted whelping date is wrong by the same margin
The cycle looks like an inexplicable failure rather than a timing error

And this is not a rare footnote. Mistimed breeding is by far the most common cause of failure to conceive in the bitch, ahead of any real fertility problem. Mistaking a spurious rise for the LH surge is one of the mechanisms behind that statistic.

Crossing 2 ng/mL is a candidate for Day 0, not a confirmation of it. Confirmation always comes from the next sample.

The confirmation rule

Treat Day 0 as provisional until a follow-up sample proves the rise is real. In practice that means three states rather than two.

State 1

Provisional

First reading above 2 ng/mL. Note the date, but commit to nothing. Retest within 24 to 48 hours.

State 2

Confirmed

Next sample is clearly higher and heading toward 6 ng/mL or above. Day 0 is now locked in. Count forward.

State 3

Retracted

Next sample is flat or fell back below 2. That was a false rise. Delete the anchor and resume testing.

State 3 is the one most breeders have no plan for. The instinct on seeing a lower number is to assume a bad sample or a bad test. Sometimes that is true, but a drop back below 2 after a brief excursion above it is a recognized pattern, not necessarily an error. The correct response is not to discard the low reading. It is to discard the anchor.

What confirmation should look like

A true rise is not subtle. De Cramer’s sampling guidance is built around exactly this: as soon as progesterone has risen above 2 ng/mL, the practitioner should collect blood daily, or at least every second day, specifically to confirm a sharp and continued rise to 6 ng/mL or above.

Situation	Sampling interval	What you are looking for
Near baseline, around 1 ng/mL, during proestrus and early estrus	About every 4 days	Any movement off baseline. This can stay flat for 10 days or longer
Authentic signs of estrus have appeared	Every 2 days	The start of the rise
Any reading above 2 ng/mL	Daily, or at minimum every 2 days	A sharp, continued rise to 6 ng/mL or above

The 2 and 6 ng/mL triggers above are on the reference laboratory scale — translate them to your analyzer’s own chart before applying them. The confirmation logic itself is scale-free: what confirms Day 0 on any machine is the shape, a sharp continued rise across consecutive samples, not any particular number.

Why single-sample timing is discouraged

De Cramer allows that a lone reading around 6 ng/mL during estrus is more likely to be reliable, and that good results can be obtained on that basis with fresh semen. Even so, he states that a single progesterone reading is generally not advised. For critical breedings — frozen or chilled semen, compromised semen, or an atypical cycle — an accurate estimate is best achieved using three, four, or more assays to cover the LH peak, ovulation, and onset of the fertile period.

The arithmetic that makes daily testing obvious

The reason breeders anchor on a single crossing is almost never ignorance. It is friction: another clinic visit, another appointment, another wait for a send-out result. De Cramer identifies the same barrier from the clinical side — progesterone assays have been available from commercial laboratories for years, but turnaround time impedes their usefulness in cases where an immediate decision is needed. When each additional data point is expensive and slow, the temptation to act on the one you already have is strong.

That calculus changes when testing happens where the dog already is. An in-house quantitative analyzer removes the two frictions that cause under-sampling — travel and turnaround — which is exactly what the confirmation rule requires. The PETlife Pro-DX Immunofluorescence Analyzer from Wondfo USA runs the canine progesterone (cProg) test on 75 µL of sample with results in about 15 minutes, with no calibration or maintenance step, and it accepts either whole blood or serum and plasma depending on the kit. A same-day answer is what lets you retest tomorrow instead of guessing today.

Log the whole curve, not the last number

A false rise is only visible as a shape. Two numbers in a notebook will not reveal it; a plotted series will. Recording every result — including the one that fell back — is what turns a confusing cycle into a readable one, and gives you a reference for how this particular bitch behaves next season. The free Pup Planner app plots test results over time and keeps them attached to the dog rather than to a notebook.

Frequently asked questions

My dog’s progesterone went up and then came back down. Is the test broken?

Not necessarily. A spurious rise as high as 2 to 3 ng/mL followed by several days well below 2 is a recognized pattern described in the clinical literature. Keep testing on the same analyzer and wait for the second, true rise. If you suspect a genuine testing problem, sample handling and platform differences are the usual causes.

How do I tell a false rise from a slow true rise?

You cannot, from a single pair of readings. That is the point of the confirmation rule: a true rise continues steeply toward 6 ng/mL and above, a false rise returns below 2. Only additional samples separate them, which is why daily testing starts the moment you cross 2.

Does a false rise mean something is wrong with my dog?

Not in itself. It is described as a clinical observation in otherwise normal cycles. Persistent failure of progesterone to rise across a full estrus is a different situation and is worth discussing with your veterinarian.

Sources

Merck Veterinary Manual. Breeding Management of Bitches. In: Management of Reproduction: Dogs and Cats. Merck & Co., accessed September 2026.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00. Sections on the number of assays required, sampling intervals, and spurious progesterone rises.

Wondfo USA. PETlife Pro-DX Immunofluorescence Analyzer, published test menu specifications.

Keep reading

When to start and how often to test.

Thresholds are analyzer-specific

Which numbers transfer between machines.

Threshold values in this article are drawn from published veterinary literature and are assay-dependent: absolute numbers are not interchangeable between analyzers. Always interpret results against the reference range for the instrument you are using. This article is educational and is not a substitute for veterinary advice.

Dog Progesterone vs. Human Progesterone: Same Hormone, Different Rules

Progesterone is one molecule. The version circulating in a Labrador is chemically identical to the version circulating in a person, which is precisely why laboratory instruments designed for human medicine can measure canine samples at all.

Almost everything else about how that molecule behaves is different between the two species, which is what makes the dog vs human progesterone comparison worth laying out properly. And because most people arrive at canine breeding with some background intuition from human reproductive health, those differences are a persistent source of confusion. Several widely held assumptions about progesterone are correct for humans and flatly wrong for dogs.

The four differences that matter most

In dogs progesterone rises before ovulation. In humans it rises after.
Dogs release immature eggs that need about 2 more days. Breeding on ovulation day is breeding early.
The canine placenta makes no progesterone. The corpus luteum is the sole source for the entire pregnancy.
Dogs have no maternal recognition of pregnancy, so progesterone cannot reveal whether a bitch conceived.

1. In humans it confirms ovulation. In dogs it predicts it.

This is the most consequential difference, and everything else in breeding management follows from it.

Figure 1. Schematic, not to scale. The canine follicle luteinizes strongly before it ruptures, so progesterone is already climbing on the approach to ovulation. This is the entire basis of canine ovulation timing.

In humans, the follicle releases the egg first and only then collapses into a corpus luteum, which begins producing progesterone. A rise during the second half of the cycle is therefore retrospective evidence: it tells you ovulation has already occurred. That is exactly how mid-luteal progesterone testing and at-home ovulation confirmation products are used in human fertility care.

The canine follicle luteinizes unusually strongly before rupture. Concannon, Hansel and McEntee documented this preovulatory luteinization in Biology of Reproduction as early as 1977, showing progesterone rising in step with the LH surge rather than after it. Progesterone therefore begins climbing in the days leading up to ovulation, which converts it from a confirmation tool into a forecasting tool.

In a woman, a progesterone rise means the window has closed. In a dog, it means the window is about to open.

2. Dogs ovulate eggs that are not ready yet

Human oocytes are released mature and are fertilizable almost immediately, with a viable window measured in roughly 12 to 24 hours. Insemination is therefore timed to coincide with ovulation.

Bitches release primary oocytes that require a further 2 days of maturation inside the oviduct before fertilization is possible. As Kurt De Cramer summarises it in his reference on the canine reproductive cycle: canine eggs cannot be fertilized immediately after ovulation because they need another 2 days to mature. Breeding on the day of ovulation is, in dogs, breeding early.

3. The cycle structure is not comparable

Humans are polyestrous with roughly monthly cycles and no true anestrus. Dogs are monoestrous, typically cycling once or twice per year, with a long obligatory anestrus between cycles.

The canine cycle is also far more elastic than a human one. Drawing on Johnston, Root Kustritz and Olson’s Canine and Feline Theriogenology, proestrus averages 9 days but can range from 1 to 27 days in extreme cases; Beijerink’s work puts estrus at an average of 9 days with a range of 3 to 21. No human cycle varies like that, and it is why counting days from the first sign of heat does not work in dogs.

One further practical consequence: a missed canine cycle is not a matter of trying again in four weeks. It may mean waiting six months or more. That asymmetry is why breeders invest in precise timing at all.

4. Where the progesterone comes from during pregnancy

In human pregnancy, the corpus luteum supports the early weeks, then hands over. Around weeks seven to nine, the placenta becomes the dominant source of progesterone in what is known as the luteal-placental shift. After that transition, the ovaries are no longer required to maintain the pregnancy.

Dogs have no such shift. As Kowalewski and colleagues have documented across a series of reviews on canine luteal and placental function, the absence of placental steroidogenic activity in this species makes the corpus luteum the sole source of pregnancy-supporting progesterone. There is no backup system and no handover. Gorlinger and colleagues established that concentrations above roughly 2.6 ng/mL are required throughout the entire pregnancy to maintain it.

Dog

Corpus luteum → corpus luteum → corpus luteum. One source, start to finish. Removing the ovaries at any stage ends the pregnancy, generally within 48 to 56 hours.

Human

Corpus luteum → luteal-placental shift at weeks 7–9 → placenta. After the handover, the ovaries are no longer required.

5. Dogs have no maternal recognition of pregnancy

In humans and most other mammals, the embryo must actively signal its presence to keep the corpus luteum alive. In humans that signal is hCG, and it is the basis of every pregnancy test on a pharmacy shelf. Without it, the corpus luteum regresses and the cycle restarts.

Dogs skip this step entirely. The canine corpus luteum persists for roughly two months after every ovulation regardless of whether conception occurred, so no rescue signal is needed. De Cramer states the clinical consequence flatly: the progesterone profiles of pregnant and non-pregnant bitches do not differ significantly, and therefore progesterone cannot be used for pregnancy diagnosis.

Two things follow from this, and both trip people up:

There is no progesterone-based pregnancy test in dogs, and there never will be. A bitch who did not conceive shows the same elevated progesterone as a pregnant one. Canine pregnancy testing uses relaxin, which is produced by placental tissue and is therefore genuinely pregnancy-specific.
Pseudopregnancy in dogs is a normal endocrine state, not a disorder. A non-pregnant bitch is, hormonally speaking, running a pregnancy program. Nesting behavior, mammary development, and even lactation can follow, and none of it indicates anything went wrong.

6. The end of pregnancy looks completely different

Human progesterone stays high through to delivery. Labor onset involves a functional withdrawal at the tissue level rather than a dramatic collapse in circulating concentration, which is why measuring progesterone is not a useful way to predict when a woman will go into labor.

Dogs undergo an abrupt prepartum luteolysis. De Cramer and Nöthling, writing in Theriogenology in 2018, quantified how tightly this tracks labour: below 2.8 ng/mL there is a 99% probability of whelping within 48 hours, and below 1.0 ng/mL that probability reaches 100%. Because the drop is both large and closely linked to labor onset, it is genuinely usable as a clinical predictor in dogs in a way it is not in humans. It underpins the temperature drop breeders traditionally watch for, and it is one input into timing an elective cesarean.

7. Dog vs human progesterone numbers are not comparable

Even when both species are measured in the same units on the same instrument, the reference points do not map onto each other.

	Dog	Human
Rise relative to ovulation	Before	After
Value at ovulation	Approximately 5 to 8 ng/mL	Still near baseline
Peak in a non-pregnant cycle	Wide range, often 15 to 90 ng/mL	Roughly 5 to 20 ng/mL mid-luteal
Source in pregnancy	Corpus luteum only, throughout	Corpus luteum, then placenta
Distinguishes pregnant from non-pregnant	No	Yes, in combination with hCG
Predicts onset of labor	Yes, via a sharp prepartum drop	Not usefully
Cycle frequency	Once or twice per year	Roughly monthly

The row that surprises people most is the peak. A non-pregnant bitch in diestrus routinely reaches progesterone concentrations several times higher than a woman’s mid-luteal peak, and sustains them for weeks. Nothing is wrong. That is simply what a normal canine luteal phase looks like.

One caution on the canine column: those figures come from laboratory assays, and progesterone values are not interchangeable between analyzers. Nöthling and De Cramer measured chemiluminescence readings averaging only 85% of paired radioimmunoassay values on canine samples, with a 95% confidence interval spanning 58% to 112%. Read your own results against the reference range for your instrument, as covered in why your analyzer’s chart doesn’t match the textbook.

8. Why human progesterone tests are not a shortcut

Given the molecule is identical, it is a reasonable question: why not use an inexpensive human at-home progesterone test on a bitch?

Four reasons it does not transfer

Sample type. Many consumer products measure a urinary metabolite (PdG) or use saliva. Neither has an established, validated relationship to serum progesterone in dogs.
Calibration range. Human assays are optimized around human decision points. The canine critical range of roughly 1 to 10 ng/mL is where breeding decisions live.
Reporting format. Consumer tests report a threshold crossing. De Cramer notes that semi-quantitative progesterone kits proved much less useful and reliable than quantitative assays returning an actual number.
The question is different. A human test answers “did ovulation happen.” A breeder needs “when will it happen, and when should I breed.”

Human laboratory analyzers, on the other hand, are widely and legitimately used for canine samples in veterinary reference laboratories. Dedicated veterinary assays go a step further and are calibrated specifically for canine serum — the canine progesterone (cProg) test on the PETlife Pro-DX, for example, is supplied in whole-blood and serum/plasma versions with its own published reference range. The important caveat either way is that different platforms produce meaningfully different numbers on the same canine sample.

Buying a test? Check it is built for dogs

The same molecule is sometimes an opening for a human-market kit to be repackaged and sold for canine use far below the price of a validated veterinary test. It may return a number, but a number measured and interpreted by the wrong rulebook is worse than no number at all. Before you rely on any progesterone test for breeding, confirm all five:

Validated for canine samples. The manufacturer states canine (not only human) validation and publishes a canine reference range — not a human one you are expected to reinterpret.
Quantitative, not a threshold. It returns an actual concentration in ng/mL, not a “positive/negative” line or a coarse band. Semi-quantitative kits have repeatedly proven less reliable for breeding.
Covers the canine decision range. Resolution across roughly 1–10 ng/mL, where every breeding decision is made, rather than a range centred on human physiology.
Right sample type. Serum, plasma or whole blood — not a urinary metabolite (PdG) or saliva, neither of which has a validated relationship to serum progesterone in dogs.
Platform-honest thresholds. Its cut-offs cite canine breeding literature and it does not claim a number is comparable across instruments. Thresholds belong to the assay that produced them — see why your analyzer’s chart doesn’t match the textbook.

If a test cannot answer these, treat an unusually low price as the tell: it is often a human assay sold without the canine validation, range or interpretation that breeding decisions require.

A brief note on cats

Queens differ again. Cats are induced ovulators: ovulation is triggered by mating rather than occurring spontaneously on a cycle. Without a mating stimulus there is generally no ovulation and no luteal progesterone rise at all. This means the entire logic of serial progesterone testing for ovulation timing, so central to dog breeding, does not transfer to cats.

The takeaway

Comparative physiology is not trivia here. Nearly every common progesterone mistake in dog breeding traces back to importing a human assumption:

Breeding on the day progesterone confirms ovulation, because in humans that is the fertile moment
Interpreting sustained high progesterone in a non-pregnant bitch as evidence of pregnancy
Assuming a single test can answer the timing question, as a single mid-luteal draw often can in human care
Expecting a consumer progesterone product to translate across species

The molecule is the same. The rules are not. Working from the canine rules is what makes the testing worth doing.

Frequently asked questions

Is dog progesterone the same hormone as human progesterone?

Yes, chemically identical. That is why human laboratory analyzers can measure canine samples. What differs is the timing, the source during pregnancy, the concentrations, and what the result means.

Can I use a human progesterone test on my dog?

Consumer at-home tests, no. They typically measure a urinary metabolite or saliva rather than serum, report a yes or no rather than a value, and are calibrated for human decision points. Veterinary laboratories do routinely run canine serum on human-derived analyzer platforms, and dedicated veterinary assays are calibrated for canine samples — both are a different thing from a pharmacy test.

Why is a dog’s progesterone so much higher than a woman’s?

The canine luteal phase is simply built differently. Peak concentrations in diestrus can run several times a human mid-luteal peak and stay elevated for weeks, in pregnant and non-pregnant bitches alike. It is normal.

Do dogs have hCG?

No. hCG is the human pregnancy-recognition signal, and dogs have no equivalent. Canine pregnancy testing relies on relaxin, which comes from placental tissue and only appears once placentation is underway.

Sources

Concannon PW, Hansel W, McEntee K. Changes in LH, progesterone and sexual behavior associated with preovulatory luteinization in the bitch. Biol Reprod. 1977;17(4):604–613.

Kowalewski MP. Endocrine and molecular control of luteal and placental function in dogs: a review. Reprod Domest Anim. 2012.

Gorlinger S, Galac S, Kooistra HS, Okkens AC. Hypoluteoidism in a bitch. Theriogenology. 2005;64(1):213–219.

De Cramer KGM, Nöthling JO. The precision of predicting the time of onset of parturition in the bitch using the level of progesterone in plasma during the preparturient period. Theriogenology. 2018;107:211–218.

Johnston SD, Root Kustritz MV, Olson PNS. Canine and Feline Theriogenology. WB Saunders; 2001.

Beijerink N. Endocrinology of physiological and progestin-induced canine anoestrus [dissertation]. Utrecht University; 2007.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Keep reading

Practical guide

Applying the canine rules to a real cycle.

After the breeding

Due dates, whelping, and pregnancy diagnosis.

Thresholds are analyzer-specific

Which numbers transfer between machines.

Threshold values in this article are drawn from published veterinary literature and are assay-dependent: absolute numbers are not interchangeable between analyzers. This article is educational and describes general comparative physiology. It is not veterinary or human medical advice. Consult your veterinarian for breeding and reproductive decisions in animals, and a physician for questions about human reproductive health.

Progesterone After the Breeding: Due Dates, Whelping, and What It Cannot Confirm

Most discussion of progesterone in breeding programs stops at the moment of insemination. That is understandable, since timing is where the tool earns its keep. But progesterone has two further jobs after the breeding, and one very prominent job it cannot do at all. The first is the progesterone whelping date: the most accurate due-date prediction available in dogs.

Key takeaways

The LH surge is the most accurate whelping anchor: about 65 days. Ovulation gives 63 days and fertilization 61 days, both less accurate.
Prediction from the first rise past ~2 ng/mL lands within ±1 day 67% of the time, ±2 days 90%, ±3 days 100%.
Below 2.8 ng/mL there is a 99% probability of whelping within 48 hours; below 1.0 ng/mL, 100%.
Progesterone cannot diagnose pregnancy in dogs. Use relaxin, ultrasound, or radiography instead.

If you run a Finecare Vet or Pro-DX

The progesterone whelping date: the best due date you will get

Canine gestation is often quoted as 58 to 68 days, which sounds imprecise enough to be nearly useless for planning. That range exists almost entirely because it is measured from the breeding date, and breeding dates are a poor anchor. Fresh sperm can wait several days in the reproductive tract, so a bitch bred on the same calendar day as another may fertilize two or three days later.

Measured from a hormonal event instead, gestation is far more consistent. Kurt De Cramer sets out the three anchors and, importantly, ranks them: pregnancy lengths based on the LH surge, ovulation and fertilization are respectively 65, 63 and 61 days, with the latter two less accurate than the former. The order surprises people, because ovulation feels like the more concrete event.

Anchor point	Days to whelping	Relative accuracy
LH surge / Day 0 (progesterone around 2 ng/mL)	65	The most accurate of the three
Ovulation (progesterone 5 to 8 ng/mL)	63	Less accurate than the LH surge
Fertilization (progesterone around 10 ng/mL)	61	Least accurate of the three
Date of breeding	58 to 68	Poor

The LH surge, not the breeding date, is the best predictor of whelping. If you recorded nothing else during the cycle, record Day 0.

How accurate is “accurate”?

It is worth being precise about this, because “progesterone predicts the due date to the day” is an overstatement that gets repeated a lot. Kutzler, Mohammed, Lamb and Meyers-Wallen, publishing in Theriogenology in 2003, measured the accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone. Using the date on which progesterone first exceeded 1.8 ng/mL, they found:

67%

land within ±1 day

90%

land within ±2 days

100%

land within ±3 days

So plan the whelping window, not the whelping day. A one-in-three chance of being off by more than 24 hours is exactly the margin that catches breeders who booked travel for the calculated date.

The two curves that look almost the same

Before going further, it helps to see what progesterone actually does across the eight or nine weeks after ovulation — and, crucially, what it does in a bitch who did not conceive.

Figure 1. Schematic comparison. For roughly fifty days the two profiles are practically indistinguishable. Only the sharp prepartum luteolysis in the pregnant bitch separates them — and by then the puppies are arriving.

The prepartum drop

In the bitch, labor is preceded by a sharp collapse in progesterone as the corpora lutea are actively broken down. De Cramer and Nöthling quantified how tightly this tracks parturition in Theriogenology in 2018, and their thresholds are what turn the number into a usable countdown.

Progesterone	What it means	What to do
5 ng/mL or above	Under 2% chance of spontaneous whelping in the next 12 hours	Low risk. Overnight observation is probably not needed tonight
Below 2.8 ng/mL	99% probability of whelping within 48 hours	Prepare
Below 2 ng/mL	Most are within 48 hours of onset of parturition	High alert for 48 hours
Below 1 ng/mL	100% probability of whelping within 48 hours; very likely within 24	High alert for 24 hours

That top row is the underrated one. Knowing a bitch is not going to whelp tonight is worth as much to a tired breeder as knowing that she is.

An important limitation on cesarean timing

De Cramer and Nöthling state directly, in the same work that produced these thresholds, that controlled studies large enough to be convincing are still required before it can be considered safe to routinely perform a cesarean section once progesterone has decreased below a defined threshold. Use these numbers as one input to a conversation with your veterinarian, not as a surgical decision rule. This is covered in more depth in timing an elective C-section.

Temperature monitoring at home remains valuable, but it is noisy. It is easily confounded by ambient conditions, activity, and inconsistent technique, and a single reading is difficult to interpret. Progesterone measures the underlying event directly, which is why in-clinic and in-house analyzers that return a quantitative result the same day — such as the PETlife Pro-DX, which runs a canine progesterone (cProg) test on 75 µL of whole blood, serum, or plasma in about 15 minutes — are useful in the final week.

Black and white photograph of a dam nursing her litter, born within the window a progesterone whelping date predicts — A due date accurate to within a couple of days changes how a whelping is staffed and supplied. *Photo via Pexels.*

What progesterone will never tell you

This surprises people

Progesterone cannot diagnose pregnancy in dogs. Not with a better assay, not with more frequent sampling. As De Cramer puts it: the progesterone profiles of pregnant and non-pregnant bitches do not differ significantly, therefore progesterone cannot be used for pregnancy diagnosis.

The reason is a genuine peculiarity of canine reproductive physiology. In dogs, the corpus luteum forms and persists after every ovulation, whether or not conception occurs, and it produces progesterone on essentially the same schedule either way. Dogs lack the maternal recognition of pregnancy signal that most species use to rescue the corpus luteum. There is nothing to rescue, because it was never going to regress on schedule in the first place.

The consequence is the pair of curves in Figure 1 above: profiles that run nearly in parallel through most of diestrus, diverging only at the very end. A non-pregnant bitch spends roughly two months with progesterone concentrations that would indicate pregnancy in almost any other species. This is also why pseudopregnancy is so common and so convincing in dogs.

What to use for pregnancy diagnosis instead

Days 21–28

Relaxin test

Pregnancy-specific. Relaxin comes from placental tissue, so a positive means placentation.

Days 25–30

Ultrasound

Confirms pregnancy and fetal viability. Unreliable for counting puppies.

Day 55+

Radiography

The most reliable puppy count, once fetal skeletons mineralize.

Days 25–30

Palpation

Operator-dependent, and the window closes quickly.

A common and sensible protocol combines relaxin or ultrasound in the fourth week to confirm pregnancy, then radiography in the final week to establish the count before whelping.

Progesterone during pregnancy, and a word on supplementation

Although progesterone cannot tell you whether a bitch is pregnant, it does have a role once pregnancy is confirmed by another method. Drawing on Gorlinger and colleagues’ work on hypoluteoidism, concentrations above roughly 2.6 ng/mL are required throughout the entire pregnancy to maintain it, and midpregnancy peaks typically run 15 to 90 ng/mL before declining. Following Verstegen-Onclin and Verstegen’s review of canine pregnancy endocrinology, serum progesterone is commonly monitored every one to two weeks in females with a history of pregnancy failure or luteal insufficiency.

Because dogs depend entirely on luteal progesterone throughout gestation, with no placental production to take over, supplementing a bitch with a history of loss has obvious intuitive appeal. It is also a decision that belongs firmly with a veterinarian. True luteal insufficiency is uncommon, most pregnancy losses have other causes, and De Cramer is explicit that progestogen supplementation must be discontinued before the expected parturition date to avoid prolonged gestation and fetal death.

Frequently asked questions

How accurate is a due date calculated from progesterone?

Counting 65 days from the LH surge is the most accurate approach. Kutzler and colleagues found prediction from the first rise past about 2 ng/mL correct within ±1 day in 67% of cases, ±2 days in 90%, and ±3 days in 100%. Plan a window, not a date.

What progesterone level means whelping is close?

De Cramer and Nöthling found that below 2.8 ng/mL there is a 99% probability of whelping within 48 hours, and below 1.0 ng/mL that probability reaches 100%. Conversely, 5 ng/mL or above means under a 2% chance of spontaneous whelping in the next 12 hours.

Can progesterone be used to schedule a cesarean section?

It is used as an input, but the researchers behind the thresholds explicitly note that sufficiently large controlled studies are still needed to confirm it is safe to schedule surgery routinely on a progesterone threshold alone. This is a veterinary decision.

Why can’t a progesterone test confirm pregnancy in a dog?

Because the corpus luteum persists after every ovulation whether or not conception occurred. Pregnant and non-pregnant bitches produce nearly identical progesterone profiles for most of the luteal phase, so there is no signal to detect.

Sources

Kutzler MA, Mohammed HO, Lamb SV, Meyers-Wallen VN. Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration. Theriogenology. 2003;60(6):1187–1196.

Gorlinger S, Galac S, Kooistra HS, Okkens AC. Hypoluteoidism in a bitch. Theriogenology. 2005;64(1):213–219.

Verstegen-Onclin K, Verstegen J. Endocrinology of pregnancy in the dog: a review. Theriogenology. 2008;70(3):291–299.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Keep reading

Timing an elective C-section

What the prepartum thresholds support, and what they don’t.

Why this happens

Dog vs. human progesterone

The physiology behind the missing pregnancy signal.

Milestone concentrations and breeding windows.

Your analyzer’s chart vs. the textbook

Why Two Progesterone Results Disagree: Assays, Units, and Sample Handling

It is a scenario that unsettles a lot of breeders the first time it happens. A sample drawn Monday morning at one clinic reads 4.2 ng/mL. The same bitch, sampled the same day and sent to a reference laboratory, comes back at 7.8. One of them must be wrong.

Usually neither is wrong. Understanding why progesterone results differ across platforms turns a confusing result into a manageable one — the measurement is genuinely more variable than most people expect.

Key takeaways

Different assay platforms produce genuinely different numbers on the same canine sample, by margins large enough to move a breeding decision.
Because timing depends on detecting a rise, internal consistency matters more than absolute accuracy. Pick one platform and stay on it for the whole cycle.
Check the unit on every report. ng/mL and nmol/L differ by a factor of about 3.18.
Separate serum promptly and avoid hemolysis. Handling changes the answer.

Why progesterone results differ between methods

Several distinct technologies are in routine use for canine progesterone, and they do not produce interchangeable numbers.

Radioimmunoassay (RIA). Historically the reference method, and the basis for many of the threshold values breeders still quote. Increasingly rare in practice.
Chemiluminescence immunoassay (CLIA and ECLIA). The current workhorse of reference laboratories, adapted from human clinical chemistry platforms.
Dry-slide and cartridge-based immunoassays. In-house bench analyzers offering same-day results in the clinic.
Fluorescence immunoassay, including lateral-flow point-of-care systems. Widely used for in-clinic veterinary testing.
Semi-quantitative visual or reader-based kits. Report bands or ranges rather than a precise concentration.

The gaps between them have been measured directly. Nöthling and De Cramer compared the Siemens Immulite chemiluminescence assay against the Coat-A-Count radioimmunoassay on blood collected at the same time from the same bitches. On average, the Immulite result was just 85% of the RIA value, with a wide scatter around that mean (95% confidence interval 58% to 112%), and 88% of Immulite readings were lower than their RIA counterparts.

Read that confidence interval again, because it is the number that matters. A 15% average shift you could in principle correct for. A spread running from 42% low to 12% high on an individual sample you cannot.

In-house analyzers show the same pattern. Østergård Jensen and colleagues, publishing in Veterinary Clinical Pathology, validated a dry-slide immunoassay for canine plasma against both chemiluminescence and mass spectrometry. They found a significant difference between the dry-slide and chemiluminescence results, and a proportional bias when the dry-slide method was compared with mass spectrometry — with chemiluminescence correlating more closely to the mass spectrometry reference.

Figure 1. Illustrative, not measured data. The point is the spread: one draw can read anywhere from “just surged” to “ovulating” depending on the platform, which is why mixing methods mid-cycle destroys the trend you are trying to read.

Put plainly: a 2.0 ng/mL threshold established on one platform is not automatically a 2.0 ng/mL threshold on another. This has direct consequences for how you read your own analyzer’s chart, which is covered in more depth in why your analyzer’s chart doesn’t match the textbook.

The one rule that solves most of this

Pick one testing method and stay on it for the entire cycle. Internal consistency matters more than absolute accuracy.

Because canine ovulation timing is fundamentally about detecting a rise rather than hitting an exact value, an assay that reads consistently low is still perfectly usable, as long as every sample in that cycle went through the same instrument. What breaks the reading is mixing platforms mid-cycle, because you can no longer tell whether a change reflects the dog or the machine.

If you genuinely must switch mid-cycle, note it prominently in your records and expect a step change that has nothing to do with physiology.

Units: ng/mL versus nmol/L

This one catches people out constantly, particularly when a report comes from a laboratory outside the United States or from a platform configured for human medicine. Progesterone is reported in nanograms per millilitre (ng/mL) in most North American veterinary practice and in nanomoles per litre (nmol/L) in much of Europe and in many clinical chemistry systems.

ng/mL	nmol/L (approx.)	Interpretation
1.0	3.2	Baseline
2.0	6.4	LH surge / Day 0
2.5	8.0	Day 0 confirmed
5.0	15.9	Ovulation
10.0	31.8	Approaching fertile window
20.0	63.6	Established luteal phase

The trap

A result of “6.4” looks like a comfortable post-ovulation number to anyone reading in ng/mL. In nmol/L it means the bitch has only just surged and the breeding is still four days out. The arithmetic is easy — multiply ng/mL by 3.18, or divide nmol/L by 3.18. The danger is failing to notice the unit at all.

Sample handling changes the answer

A laboratory technician preparing a canine blood sample, since handling is one reason progesterone results differ between labs — What happens between the draw and the analyzer matters. Validation work has measured losses after only 12 to 24 hours at room temperature. *Photo via Pexels.*

Progesterone is reasonably robust compared with some hormones, but it is not indestructible. The Østergård Jensen validation put numbers on this, and they are larger than most breeders assume:

Handling condition	Measured effect
Stored at room temperature for 12 to 24 hours	Concentrations fell to 57% to 96% of the initial value
Frozen at −80°C	Concentrations reduced by 17% to 27%
Hemolytic and lipemic samples	Minor changes observed

The freezing result is the counterintuitive one. Freezing feels like preservation; here it was associated with a measurable loss rather than a hold. That alone is a reason not to bank samples and run them later during a cycle you are actively timing.

Separate serum promptly. Leaving whole blood sitting on the clot allows drift.
Avoid hemolysis and lipemia. Both can interfere with immunoassay readings. A fasted sample and clean venipuncture help.
Confirm the accepted sample type. Some analyzers are validated for serum only, others accept whole blood or plasma, and some manufacturers supply separate kits for each. EDTA and heparin are not always interchangeable.
Do not assume freezing preserves the value. See the table above.
Sample at a consistent time of day. This does not eliminate variation, but it removes one source of noise from a serial curve.

Point-of-care systems differ in what they accept. The PETlife Pro-DX, for example, supplies the canine progesterone (cProg) test in separate whole-blood and serum/plasma versions, both running on 75 µL with results in about 15 minutes. Using the kit that matches your sampling workflow removes one avoidable source of variation, and testing on site removes the room-temperature transit window entirely.

When semi-quantitative kits are enough, and when they are not

Kits that report a range rather than a number have a legitimate role. If your question is “has the rise started yet, or should I test again in three days,” a categorical answer is entirely sufficient and considerably cheaper.

Where they fall short is at the decision point. De Cramer is blunt about it: progesterone test kits performing semiquantitative evaluation proved much less useful and reliable than quantitative assays that give an accurate numerical value. Distinguishing 2.2 from 3.4 ng/mL can move Day 0 by a full day, and with frozen semen a full day is the whole margin. For high-stakes breedings, use a quantitative method through the critical window even if a screening kit got you there.

What to record alongside the number

Date and time of the draw

Location and analyzer or lab

The unit as printed on the report

Sample type, if known

Cycle day from first proestrus signs

Keeping the platform recorded alongside each result is what makes a multi-year record genuinely comparable. Without it, a value from two seasons ago is a number you cannot safely trust against today’s. The free Pup Planner app keeps test results plotted against the individual dog, which makes the series readable rather than a stack of loose slips.

Frequently asked questions

Which progesterone test is the most accurate?

Chemiluminescence assays correlate most closely with mass spectrometry among the widely available methods, as Østergård Jensen and colleagues found, and radioimmunoassay was the historical reference. But for ovulation timing, the practical answer is that consistency across the cycle matters more than which platform you chose.

How do I convert nmol/L to ng/mL?

Divide by 3.18. So 6.4 nmol/L is about 2.0 ng/mL, and 15.9 nmol/L is about 5.0 ng/mL. To go the other way, multiply ng/mL by 3.18.

Can I switch labs partway through a cycle?

It is best avoided. If circumstances force it, record the switch clearly and expect a step change in the numbers that reflects the instrument rather than the dog. Do not read that step as a physiological event.

Sources

Nöthling JO, De Cramer KGM. Comparison of progesterone assay by chemiluminescence or radioimmunoassay for clinical decision-making in canine reproduction.

Østergård Jensen S, et al. Validation of a dry-slide immunoassay for progesterone analysis in canine plasma in a clinical setting. Vet Clin Pathol. 2022.

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.

Keep reading

Which numbers transfer between machines, and which never do.

Milestone concentrations and breeding windows.

The false rise

Why one reading above 2 ng/mL isn’t Day 0.

This article is educational and is not a substitute for veterinary advice. Assay selection, sample handling protocols, and result interpretation should be discussed with your veterinarian or testing laboratory.

Why one reading above 2 ng/mL isn’t Day 0.

Building a Progesterone Testing Schedule: When to Start and How Often to Test

Most missed breedings do not come from misreading a progesterone result. They come from not having enough results to read. A bitch tested on day 8 of proestrus and again on day 14 has left a six-day hole in the record, and the LH surge almost certainly happened inside it.

A good progesterone testing schedule is not about testing constantly. It is about testing loosely when nothing is happening and tightly when everything is. This article covers how to build that cadence.

Before you use any number on this page

Progesterone thresholds are specific to the assay that produced them. Different analyzers report systematically different values on the same blood sample, so a threshold from one instrument is not valid on another. Read your results against the reference range published for your analyzer. What does transfer between machines is the pattern — baseline, rise, confirmation — and the day counts. See how Mini Vidas, Vcheck and Finecare readings compare and why your analyzer’s chart doesn’t match the textbook.

Key takeaways

Draw a baseline sample around days 5 to 7 of proestrus. A confirmed low result is what makes every later result meaningful.
Let the result, not the calendar, decide the next interval: about every 4 days near baseline, every 2 days once estrus signs appear, daily once you pass 2 ng/mL.
Keep testing until you see a sharp continued rise to 6 ng/mL or above. A single crossing of 2 is not Day 0.
Critical breedings need three, four or more assays. A single reading is not advised.

If you run a Finecare Vet or Pro-DX

Start earlier than feels necessary

The single most common scheduling error is starting late. Breeders often wait until the bitch is clearly flagging and standing, at which point ovulation may already be behind them. Kurt De Cramer gives the same advice from the clinical side: less experienced practitioners are specifically advised to start collecting blood earlier in the estrous cycle rather than later, because experienced clinicians are better at judging when the rise is likely to begin.

A reasonable default is to draw a baseline sample around days 5 to 7 after the first sign of proestrus bleeding. That first result is usually well under 1 ng/mL, and that is exactly the point. A confirmed baseline tells you the rise has not started yet, which converts every subsequent result into a comparison rather than an isolated number.

Two situations argue for starting even earlier:

Bitches with a history of early ovulation. If a previous cycle surged on day 7, start on day 4 this time. Individual dogs repeat their own pattern more closely than they follow the breed average.
Bitches with minimal or hidden discharge. Small breeds and fastidious groomers can obscure the onset of proestrus by several days, meaning your “day 5” may actually be day 9.

The escalating interval

Think of the schedule as tightening in stages, triggered by the result rather than by the calendar. The pattern looks like this across a typical cycle:

Figure 1. An illustrative six-test cycle following De Cramer’s sampling guidance, with values on the reference laboratory (CLIA) scale. Note that D12 is only a candidate Day 0 — it is the confirmed rise past 6 ng/mL on D14 that makes it real. The sampling is densest exactly where that confirmation has to happen. The values in this example run ahead of the day-by-day bands in the milestone table — 5.1 the day after Day 0, 11 the day after that. Individual cycles differ by that much, which is precisely why the confirmation step exists; what transfers from this figure is the sampling interval, not these particular numbers. On a Vcheck, Finecare/Pro-DX or other point-of-care analyzer the same trigger points sit at different numbers — see how the common analyzers compare — but the intervals transfer unchanged.

The intervals themselves come straight from De Cramer’s guidance on blood collection. The trigger values in the table are on the reference laboratory scale; on your analyzer the same triggers sit at different numbers, but the logic — loose near baseline, daily once the rise starts, stop only after confirmation — transfers to every machine.

Situation	Next test	Why
Near baseline, around 1 ng/mL	In about 4 days	Progesterone can remain close to basal for 10 days or longer during proestrus and early estrus.
Authentic signs of estrus have appeared	Every 2 days	Move on the behaviour, not on the number.
Any reading above 2 ng/mL	Daily, or at minimum every 2 days	A single crossing of 2 is not Day 0 on its own. Keep testing until a sharp continued rise is confirmed.
Confirmed sharp rise to 6 ng/mL or above	Testing has done its job	Day 0 is confirmed retrospectively. Now count forward from it.

Most straightforward cycles resolve in four to six tests. For critical breedings — frozen or chilled semen, compromised semen, or an atypical cycle — De Cramer recommends three, four, or if required even more assays, specifically to cover the three key events: the LH peak, ovulation, and the onset of the fertile period.

Do not let the calendar create gaps

Bitches do not schedule the LH surge around clinic hours. If a bitch reads 1.8 ng/mL on a Friday afternoon and your clinic is closed until Monday, you have a problem that no amount of interpretation will fix.

Plan the weekend before you reach it. A Thursday result above 1 ng/mL is the moment to confirm Saturday availability, not Friday evening.

This is one of the strongest practical arguments for in-house or in-clinic testing. As De Cramer notes, progesterone assays have been available from commercial laboratories for years, but turnaround time impedes their usefulness in cases where an immediate clinical decision is needed — which is precisely why point-of-care assays exist. A highly accurate result that arrives 36 hours later can be worth less than a slightly different scale you can read this morning and again tomorrow. Systems such as the PETlife Pro-DX return a quantitative canine progesterone (cProg) result from 75 µL of whole blood, serum or plasma in about 15 minutes, which is what makes a daily interval realistic rather than aspirational.

How frozen semen changes the plan

Everything above assumes a natural or fresh breeding, where sperm longevity absorbs some timing error. Frozen semen removes that cushion almost entirely: thawed sperm survive in the female genital tract for a period probably not exceeding 12 hours.

Frozen semen protocol adjustments

Move to daily testing once progesterone passes 1 ng/mL, rather than waiting for 2
Aim to identify Day 0 within a 12 to 24 hour window, not a 48 hour one
Consider adding direct LH testing, which requires daily sampling but pins Day 0 precisely
Book the insemination team provisionally as soon as the rise starts, targeting Days 6 and 7 after the LH surge, one day apart — the timing established by Steckler, Nöthling and Harper in a multi-sire frozen-semen insemination trial

The economics support this. Additional progesterone tests are inexpensive compared with the cost of a frozen semen shipment, a surgical or transcervical insemination, and a lost breeding season that may not come around again for six months.

Watch the shape of the curve, not just the threshold

Two results are a line. Four results are a curve, and the curve carries information the individual points do not. A bitch climbing from 0.8 to 2.4 to 9.0 ng/mL over four days is behaving very differently from one moving 0.9 to 1.6 to 2.8 over the same period, even though both crossed the same threshold.

A slow or stalling rise is worth raising with your veterinarian. It may be nothing more than individual variation, but it can also be a false rise that will fall back below 2 before the real one arrives. Either way it is a reason to keep testing rather than to assume the timeline from here is standard.

Cycles that need a different approach

Split heats

Proestrus signs appear, regress without ovulation, then return weeks later. Progesterone that never leaves baseline across a full estrus is the clue.

Silent heats

Minimal external signs with a normal underlying cycle. Found by testing on suspicion rather than on observation.

Uncertain history

Older bitches or previously mistimed cycles. Treat as a first cycle: start early, confirm a baseline.

All three are made harder by how elastic the canine cycle is. Drawing on Johnston, Root Kustritz and Olson, proestrus averages 9 days but ranges from 1 to 27 days in extreme cases; Beijerink puts estrus at an average of 9 days with a range of 3 to 21. Nothing about the calendar is reliable enough to substitute for testing.

A working progesterone testing schedule

Record the first day of proestrus discharge as accurately as you can
Draw a baseline sample around day 5 to 7
Test about every 4 days while results stay near baseline
Tighten to every 2 days once authentic estrus signs appear
Move to daily testing the moment any result exceeds 2 ng/mL
Do not lock in Day 0 until a sharp continued rise to 6 ng/mL or above is confirmed
Keep every result, including the boring baseline ones, for next cycle’s planning

That last step matters more than it looks. The baseline results are what let you start at the right point next time, and over two or three cycles they turn a generic schedule into one tuned to the individual dog. The free Pup Planner app keeps those results plotted against the dog rather than scattered across notebooks and text messages.

Frequently asked questions

When should the first progesterone test of the cycle be taken?

Around days 5 to 7 after the first sign of proestrus bleeding for most bitches. Start earlier if she has surged early in a previous cycle, or if her discharge is easy to miss. Starting too early costs one inexpensive test; starting too late can cost the season.

Is testing every other day enough?

Every 2 days is the right interval once estrus signs appear, but once any result exceeds 2 ng/mL you should move to daily. A 48 hour gap there can move your Day 0 estimate by a full day, which is most of the available margin with frozen semen.

Can I stop testing once progesterone is clearly rising?

Once you have confirmed a sharp continued rise to 6 ng/mL or above, yes. Day 0 is established and the calendar takes over. Stopping before that confirmation is what leaves you exposed to anchoring on a false rise.

Sources

De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00. Sections on the number of assays required and the interval between blood collections.

Steckler D, Nöthling JO, Harper C. Prediction of the optimal time for insemination using frozen-thawed semen in a multi-sire insemination trial in bitches. Anim Reprod Sci. 2013;142(3–4):191–197.

Johnston SD, Root Kustritz MV, Olson PNS. Canine and Feline Theriogenology. WB Saunders; 2001.

Beijerink N. Endocrinology of physiological and progestin-induced canine anoestrus [dissertation]. Utrecht University; 2007.

Keep reading

Important

The false rise

Milestone concentrations and breeding windows.

After the breeding

Due dates, whelping, and what it cannot confirm.