Progesterone Testing for Dog Breeding: A Complete Guide to Timing
Mistimed breedings are the most common cause of missed conceptions — and most missed breedings are completely preventable with progesterone testing.
Dogs are seasonally monoestrous — they go into heat roughly twice a year, and each cycle offers a narrow ovulation window that must be precisely identified for a successful breeding. Progesterone testing is the gold standard for finding that window.
How Canine Reproduction Works
Unlike many other mammals, the canine estrous cycle has four phases:
Proestrus (typically 7-10 days): Bloody vaginal discharge, swelling of the vulva. The bitch attracts males but will not allow mating. Estrogen is rising. Progesterone is baseline low (under 1 ng/mL).
Estrus (typically 5-9 days): Discharge lightens or clears. The bitch will accept mating. Progesterone rises sharply. Ovulation occurs during this phase. This is the breeding window.
Diestrus: Post-ovulation phase. Progesterone remains elevated whether pregnant or not, then declines over 60-90 days.
Anestrus: The inactive phase between cycles.
What Progesterone Testing Measures
Progesterone is a hormone produced by the corpus luteum after ovulation. Its levels rise predictably around ovulation, providing a measurable marker for cycle timing.
Key progesterone thresholds (ng/mL):
| Progesterone Level | Reproductive Event |
|---|---|
| Under 1.0 ng/mL | Proestrus — not ready |
| 1.0–2.0 ng/mL | LH Surge is occurring or imminent |
| 2.0–5.0 ng/mL | Pre-ovulation rise — getting close |
| 5.0–10.0 ng/mL | Ovulation is occurring or just occurred |
| 10.0–20.0+ ng/mL | Post-ovulation — eggs are maturing |
| 15.0–25.0+ ng/mL | Optimal breeding window (days 2-4 post-ovulation) |
Note: These thresholds can vary slightly between laboratory machines and assay methods. Always interpret results in context of the values from the same laboratory.
When and How Often to Test
Start testing early — ideally at day 5-7 of the cycle (counting day 1 as the first day of bloody discharge). Starting early ensures you don't miss a cycle that progresses faster than expected.
Testing frequency depends on where the bitch is in her cycle:
- Below 1 ng/mL: Retest in 2-3 days
- 1-3 ng/mL: Retest in 1-2 days
- 3-8 ng/mL: Retest in 1 day — breeding window is approaching
- 8+ ng/mL: Breed as soon as possible if not already breeding; determine optimal days
Using in-clinic analyzers vs. reference labs: Most veterinary clinics use in-house progesterone analyzers (Immulite, Siemens Advia, etc.). Reference labs may have slightly different values. Do not mix results from different machines when tracking a single cycle.
The LH Surge and Its Significance
Luteinizing hormone (LH) surges just before ovulation, triggering the ovaries to release eggs. The LH surge lasts only 24-48 hours, making it difficult to capture. When it occurs, progesterone is typically in the 1-2 ng/mL range.
Some veterinary clinics offer LH testing (daily blood draws are required since the surge is brief). When LH is confirmed:
- Ovulation typically occurs 24-48 hours after the LH surge
- Eggs take 48-72 hours post-ovulation to mature and become fertilizable
- Optimal breeding window: 2-4 days after LH surge (which corresponds roughly to progesterone 15-25+ ng/mL)
Timing Different Breeding Methods
Natural tie: Progesterone 10-25 ng/mL. Plan breedings on days 2-4 post-ovulation (when progesterone is 15-25+ ng/mL). A second tie 48 hours later is beneficial.
Fresh-chilled semen AI: Chilled sperm survives 24-72 hours in the female tract. Target the same 15-25 ng/mL range.
Frozen semen: Frozen/thawed sperm survives only 12-24 hours. Timing precision is most critical. Most frozen semen breedings are timed for progesterone 25-30+ ng/mL, very close to the peak. TCI is preferred for frozen semen to place sperm as close to the ovaries as possible.
Common Mistakes
Starting too late: Missing the early rise and breeding too early or too late.
Testing infrequently: Testing every 3-4 days during the critical window means missing the peak.
Using vaginal cytology alone: Vaginal cytology tracks cell maturation and is useful supplemental information but is not a substitute for progesterone testing for precise timing.
Confusing machine values: Different analyzers give different absolute numbers. A value of 6.0 on one machine and 6.0 on another machine may not represent the same biological state.
Summary
Progesterone testing is the most reliable way to time a breeding and should be used for every planned breeding. Start testing at day 5-7 of the cycle. The optimal breeding window corresponds to progesterone levels of approximately 15-25+ ng/mL (2-4 days post-ovulation). Natural tie and fresh AI have more timing flexibility than frozen semen, which requires the tightest precision. Work with a reproduction-experienced veterinarian to interpret values from your specific clinic's machine.