Progesterone Testing in Dogs: When to Breed for the Best Results

Timing is everything in dog breeding — and progesterone is the only reliable way to get it right

One of the most common reasons a breeding fails is not the stud, not the dam, and not bad luck. It is timing. A female dog's fertile window is surprisingly narrow — just a few days within a heat cycle that can last three to four weeks. Breeding even two days outside that window can result in no pregnancy at all.

Progesterone testing removes the guesswork. It is the single most reliable tool available for timing a breeding accurately, and every serious breeder uses it.

What Is Progesterone Testing?

Progesterone is a hormone produced by the ovaries. In female dogs, progesterone levels follow a predictable pattern during the heat cycle:

• They remain very low during proestrus (the early bleeding phase)
• They begin to rise sharply just before ovulation
• They peak and remain elevated during the fertile window
• They drop again if no pregnancy occurs

By measuring progesterone levels in the blood, your veterinarian can tell you exactly where your female is in her cycle and when she is ready to breed.

Why Vaginal Cytology and Day-Counting Are Not Enough

Vaginal cytology tells you that ovulation is approaching, but not exactly when it will occur. Two females with identical cytology results could be days apart in their actual fertility.

Counting days from first bleeding is even less reliable. Heat cycles vary enormously between individual dogs — a female who was ready to breed on day 10 in her last cycle may not be ready until day 16 in the next.

Progesterone testing gives you an actual number in nanograms per milliliter (ng/mL) that tells you precisely where the dog is in her cycle.

Understanding the Numbers

The key threshold most reproductive veterinarians target for breeding is 5–10 ng/mL for the first breeding, with a follow-up breeding 2 days later. Eggs are released at ovulation but require approximately 48–72 hours to mature before they can be fertilized.

When to Start Testing

Start earlier than you think you need to.

Recommended starting point: Day 5–7 from the first sign of bleeding or vulvar swelling.

Some females cycle early and will ovulate before most breeders expect. Starting on day 5 protects you from missing an early peak.

Testing frequency:

• Start every 2–3 days until you reach 2.0 ng/mL
• Once you hit 2.0 ng/mL, test every 1–2 days until you reach the breeding window

Most females will require 4–7 progesterone tests during a single heat cycle. The cost — typically $50–$100 per test — is one of the best investments you can make in a litter.

In-House vs. Reference Lab Testing

In-house analyzers give results within 30–60 minutes. They are convenient but have wider variability between machines.

Reference laboratory testing is more accurate and standardized, but results take 24–48 hours.

The most important rule: use the same machine or lab for all tests in a single cycle. Switching between labs mid-cycle gives you numbers that are not directly comparable.

For Shipped Semen and AI Breedings

If you are using chilled or frozen semen, accurate timing is even more critical. Chilled semen has a viability window of 24–72 hours. Frozen semen is viable for only 12–24 hours after thawing.

For chilled semen: reach 10–15 ng/mL, then inseminate within 24–48 hours, accounting for shipping time.

For frozen semen, the margin for error is even smaller. Coordinate with your vet and the semen bank well in advance. A missed window with frozen semen may mean a missed cycle entirely.

After the Breeding

Progesterone continues to rise after ovulation regardless of whether the female is pregnant. A high progesterone value 3–4 weeks after breeding does not confirm pregnancy. For pregnancy confirmation, use:

• Ultrasound at 25–30 days post-ovulation (most reliable for early detection)
• Relaxin hormone blood test at 28–30 days (confirms pregnancy, not litter size)

Summary

Key points to remember:

• Start testing on day 5–7 from first sign of heat
• Breed at 10–25 ng/mL; ovulation occurs around 5–10 ng/mL
• Use the same lab or machine throughout the cycle
• For AI and shipped semen, timing is even more critical
• Work with a reproductive veterinarian whenever possible

The stud dog you choose matters. The breeding you time correctly is the one that produces a litter.