Last reviewed: May 2026 · BreedTools Editorial Team · Sources cited inline and at the end of the article.
Why progesterone testing matters
Breeding at the wrong time is the single most common cause of small litters and missed pregnancies in dogs. Unlike many species, canine ovulation timing is highly variable — even between cycles in the same dog. A bitch may stand for the male on day 9 of one cycle and day 15 of the next.[1] Without progesterone testing, you are guessing.
Progesterone testing removes the guesswork. By measuring the hormone progesterone in the blood, you can pinpoint ovulation to within 24–48 hours.[1] This precision matters most for frozen semen AI (where the window is very narrow — sperm survives only 12–24 hours post-thaw),[2] but it significantly improves results for fresh-chilled AI and natural breedings as well.
Interactive — click any point
Progesterone curve through a heat cycle
Tap or click any reading to see the breeder action for that day.
Optimal — fresh AI
Best day for natural breeding or fresh AI.
2 ng/mL
LH surge
Ovulation
20 ng/mL
Eggs mature
≥25 ng/mL
Optimal AI
The hormonal timeline
Hormonal mechanism
LH surge → ovulation → fertile window
Progesterone testing detects the LH surge indirectly. Once progesterone hits ~2 ng/mL, the LH peak is happening in real time. Ovulation follows in 48 hours.
Brief surge — usually missed without daily testing. Progesterone crosses 2 ng/mL at this moment.
≈48 hours after LH peak. Progesterone reaches ~5 ng/mL. Eggs released but immature.
3. Fertile window (Day 13–16)
Eggs mature 48 hours post-ovulation. Optimal breeding day depends on AI method.
Understanding the sequence of hormonal events is essential for interpreting progesterone results. Here is what happens during a typical canine estrous cycle:
| Event | Progesterone Level | What's Happening |
|---|---|---|
| Baseline (proestrus) | < 1.0 ng/ml | Estrogen rising, follicles developing. Not yet fertile. |
| LH surge | 2.0–3.0 ng/ml | Luteinizing hormone spike triggers ovulation. Day 0 of the fertile timeline. |
| Ovulation | 5.0–8.0 ng/ml | Eggs released ~2 days after LH surge. Eggs are immature and need 48 hours to mature. |
| Oocyte maturation | 8.0–15.0 ng/ml | Eggs mature and become fertilizable. The fertile window opens. |
| Optimal breeding | 15.0–25.0 ng/ml | Peak fertility. Natural breeding or fresh AI is most effective here. |
| Late window | > 25.0 ng/ml | Fertility declining. Eggs aging. Last chance for breeding. |
| Post-fertile | > 40.0 ng/ml | Eggs no longer viable. Too late to breed this cycle. |
When to start testing
Begin progesterone testing around day 5–7 of the heat cycle (counting from the first sign of vulvar swelling or bloody discharge). For bitches with irregular cycles or a history of variable timing, start at day 3–5.
If you have access to vaginal cytology, start progesterone testing when cytology shows 50% or more cornified cells — this indicates estrogen is peaking and the LH surge is approaching.
Track your bitch's cycle history with the Heat Cycle Tracker so you have historical data to guide when to start testing in future cycles.
Testing frequency
- Every 2–3 days while progesterone is below 2.0 ng/ml (baseline)
- Every 1–2 days once progesterone rises above 2.0 ng/ml (LH surge occurring)
- Daily once progesterone is between 5.0–15.0 ng/ml (critical window)
Once you have confirmed ovulation (progesterone 5.0–8.0 ng/ml), you can calculate the optimal breeding day with confidence. Use the Breeding Window Calculator to interpret your readings and get exact breeding day recommendations for your method (natural, fresh-chilled, or frozen).
How the test works in practice
Progesterone testing is a simple blood draw — usually 1–2 mL from the jugular vein or cephalic vein. The visit takes 10–15 minutes. Your dam doesn't need to be fasted, and the test is generally well-tolerated even by anxious dogs.
- Sample type:Serum (red-top tube) is preferred. Whole blood and plasma can be used in some in-house machines but check the manufacturer's spec.
- Time of day:Morning testing is most common because most labs process samples mid-day. For in-house machines, time of day doesn't matter.
- Sample handling for shipped tests: Sample must be centrifuged within 2 hours of draw. Serum should be shipped chilled (not frozen) overnight. Hemolyzed (broken-cell) samples can give falsely elevated readings — re-draw if your vet flags hemolysis.
- Fasting: Not required, but avoid testing right after a meal — lipemic (fatty) samples can interfere with some assays.
- What you bring home: A ng/mL number (quantitative) or a range (semi-quantitative). Record it with the date, exact time, and which machine/lab was used.
Cost per test
$50–$100
Quantitative lab. In-house may be $35–$75.
Tests per cycle
4–8
Depending on how rapidly the curve moves.
Total per cycle
$200–$600
A small or missed litter costs far more.
Common mistakes (and how to avoid them)
- Testing once and assuming you have your answer. A single reading is a snapshot. You need a series to identify the LH surge and ovulation. The shape of the curve matters more than any one number.
- Starting too late. If you wait until your dam is in standing heat to test, you may miss the LH surge entirely. Begin testing every 2–3 days from day 5 of the cycle.
- Comparing across machines. A reading of 4.0 ng/mL on one in-house analyzer may correspond to 3.5 or 4.5 on another. Stick to one testing method per cycle so the curve is internally consistent.
- Ignoring vaginal cytology. Cytology (a vaginal swab examined under the microscope) shows whether estrogen is peaking. Combined with progesterone, it gives you a more complete picture — especially in dams with silent or atypical heats.
- Stopping after ovulation is confirmed. Continue testing through to 25+ ng/mL if you are using frozen semen — the optimal AI window is at peak, not just past ovulation.
- Forgetting to record. Track every reading with date, exact time, and method. Your dam will likely follow a similar pattern in future cycles, and historical data is gold.
Breeding timing by method
The optimal breeding time differs depending on the breeding method, because fresh sperm live longer than chilled sperm, which lives longer than frozen sperm.
Natural mating
2–4 days after ovulation. Sperm survive 5–7 days.
Fresh-chilled AI
2–3 days after ovulation. Sperm survive 24–48 hours.
Frozen AI
2–2.5 days after ovulation. Sperm survive 12–24 hours.
| Method | Optimal Timing | Sperm Viability | Progesterone Range |
|---|---|---|---|
| Natural mating | 2–4 days after ovulation | 5–7 days in the tract | 15–25 ng/ml |
| Fresh-chilled AI | 2–3 days after ovulation | 24–48 hours | 15–20 ng/ml |
| Frozen semen AI | 2–2.5 days after ovulation | 12–24 hours | 15–20 ng/ml (narrow window) |
Lab vs. in-house testing
Quantitative lab testing (IDEXX, Antech, or university labs) provides a precise ng/ml value and is the gold standard. Results typically take 4–24 hours depending on the lab. Cost: $50–$100 per test.
In-house machines(Mini VIDAS, Finecare, or similar immunoassay analyzers) give results in 15–30 minutes at your vet's office. These are accurate enough for breeding timing decisions but may show slight variations between machines. If your vet uses an in-house machine, ask which one — different machines use different reference ranges.
Semi-quantitative test kits (color-change kits) are less accurate and only show broad ranges. They can identify the LH surge but are not precise enough for frozen semen timing. Use them only as a screening tool, not as your primary timing method.
Reading the progesterone curve
A single progesterone reading tells you where you are right now. A series of readings tells you where you are going. The rate of rise is as important as the absolute number:
- Slow rise (0.5–1.0 ng/ml per day) — normal pre-ovulatory pattern, continue testing every 2 days
- Rapid rise (jumping from 2.0 to 8.0+ in 48 hours) — ovulation has occurred, plan breeding immediately
- Plateau (same level for 2+ days below 5.0 ng/ml) — LH surge may not have occurred yet; continue testing
- Decline — unusual in a progressing cycle; retest to confirm, and consult your reproductive vet
Record every reading with the date, time, and lab used. This historical data becomes invaluable for timing future cycles with the same bitch — many bitches follow similar patterns across cycles.
What to ask your vet
Not all veterinarians are experienced with breeding timing. If you are working with a reproductive specialist, they will guide the testing protocol. If you are working with a general practice vet, ask:
- What progesterone testing method do you use? (Quantitative lab or in-house machine?)
- What are the reference ranges for your machine?
- Can I get same-day results?
- Do you offer weekend testing? (Ovulation does not wait for Monday.)
- Can you perform vaginal cytology alongside progesterone testing?
Once you have your progesterone results, enter them into the Breeding Window Calculator for machine-specific interpretation and breeding day recommendations. After a successful breeding, calculate your expected due date with the Whelping Date Calculator.
References & further reading
- [1] Concannon PW. Reproductive cycles of the domestic bitch. Animal Reproduction Science (2011) 124:200–210. — Canonical reference on canine cycle hormonal events including progesterone, LH surge, and ovulation timing.
- [2] Linde-Forsberg C. Achieving canine pregnancy by using frozen or chilled extended semen. Veterinary Clinics of North America: Small Animal Practice (1991) 21(3):467–485. — Foundational research on frozen semen viability windows and AI timing.
- Johnston SD, Root Kustritz MV, Olson PNS. Canine and Feline Theriogenology. W.B. Saunders Company, 2001. — Standard reproductive medicine textbook used in vet school curricula.
- England GCW, von Heimendahl A (eds). BSAVA Manual of Canine and Feline Reproduction and Neonatology, 2nd Edition. British Small Animal Veterinary Association, 2010. — Practical clinical reference with detailed progesterone protocols.
- American College of Theriogenologists. Position on Canine Reproduction. theriogenology.org — Professional standards for breeding management and reproductive testing.
Related Tools
Sources: Merck Veterinary Manual (Canine Reproduction and Estrous Cycle Management); Concannon PW. Reproductive cycles of the domestic bitch (Animal Reproduction Science / Theriogenology); Society for Theriogenology (SFT) reproduction resources and continuing education materials; Davidson AP. Small Animal Theriogenology (Saunders / Elsevier). This article is for educational purposes and does not replace professional veterinary care.
Progesterone testing FAQs
1When should I start progesterone testing?
Take a baseline reading early — around day 5–7 of proestrus, or once vaginal cytology shows the bitch is moving toward estrus. It is far better to start too early (and see a flat baseline) than to start late and miss the rise through the LH surge. A single late test can leave you guessing where you are on the curve.
2How often do I need to test?
Test every other day while progesterone is still at baseline, then move to daily — or at least every second day — as soon as it starts climbing above roughly 2 ng/mL. The LH surge and ovulation happen over just a few days, so spacing tests too far apart is the most common way breeders miss the fertile window.
3What progesterone level signals the LH surge and ovulation?
As a rule of thumb, the LH surge occurs when progesterone first rises to about 2–3 ng/mL, and ovulation follows roughly two days later at around 5 ng/mL. Because a dog ovulates immature eggs, the most fertile days come several days after that. Treat these numbers as a guide, not gospel — the exact targets depend on which analyzer your vet uses.
4When do I breed for natural mating vs. fresh-chilled vs. frozen semen?
Timing tightens as sperm longevity drops. Natural and fresh breedings have the widest window — generally from a couple of days after ovulation. Fresh-chilled AI is often a single insemination about 48 hours after the ~5 ng/mL mark. Frozen semen demands the most precision — usually days 5–6 after the LH surge — because thawed sperm survive only about 12–24 hours.
5Do different progesterone machines give the same numbers?
No — and this trips up many breeders. In-clinic analyzers (IDEXX Catalyst, Finecare, miniVidas) and send-out reference labs can report meaningfully different values for the same sample. Run the whole cycle on one machine and interpret the numbers against that machine's scale; never compare a Finecare reading to an IDEXX target or switch analyzers mid-cycle.
6Why can't a single progesterone test tell me when to breed?
One value is just a snapshot. Accurate timing comes from the trend — watching progesterone climb through the LH surge to ovulation and beyond. Two bitches can sit at the same number on different days of their cycle, so the rate and direction of change, not a lone reading, is what pins down the fertile days.
7My lab reports nmol/L instead of ng/mL — how do I convert?
Multiply ng/mL by about 3.18 to get nmol/L, or divide nmol/L by 3.18 to get ng/mL. For example, 5 ng/mL is roughly 16 nmol/L. Always confirm which unit your report uses before comparing it to a breeding target, since mixing the two can put your timing off by days.
8Does my dog need to fast before a progesterone test?
No. Progesterone testing does not require fasting — it is a simple blood draw that can be done at any time of day. Drawing at a consistent time does make a tidy day-to-day trend, but it is not essential, and you should never delay a needed test just to fit a fasting schedule.
9Is progesterone testing worth the cost?
For artificial insemination, shipped fresh-chilled or frozen semen, a maiden bitch, or any history of missed or small litters, yes — the cost of testing is small next to a wasted breeding, a shipped semen unit, or an entire empty season. Some breeders of proven natural pairs test more selectively, but timing errors remain the most common cause of breeding failure.