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.
- 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.
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.
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.
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
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.