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Predicting fertility

Common sense disclaimer: As with everything else on this blog, it’s critical to seek the advice of a qualified veterinarian, preferably one that is board certified in theriogenology (reproductive science) for reproductive matters. This website, its blog, and its courses are NOT designed nor intended to replace the need for a qualified veterinarian, but instead to help educate people to to work optimally with their veterinarians. All recommendations should be reviewed with qualified professionals, such as a board certified reproductive veterinarian, prior to implementation in a breeding program. Always seek the advice of your veterinarian. Readers assume all risks associated with use of material on this site. More here.


This is a very abbreviated explanation of fertility and timing for dogs, for a complete discussion as please check out my Fertility and Timing course.

The course helps you avoid all the common mistakes and myths that surround fertility and timing for breedings

  • How to pinpoint fertility to avoid small litters, singletons, or failed pregnancies

  • How to time a breeding if you CAN'T get a progesterone test

  • The right way to predict whelping date so you aren’t left wondering and worried for days—or longer

  • How to get started with at-home testing for under $200 and what supplies you need

  • Certificate and badge of completion to enhance your professional image and credibility on your website

  • How and when eggs become fertile, what is ovulation and why is date of ovulation so important

  • What is cytology, and little-known ways it helps pinpoint fertility

The course includes a bunch of DIY at-home bonuses including

  • At-home semen analysis

  • At-home artificial insemination (AI)

  • Other methods for fertility determination if progesterone testing isn’t available

  • Confirming pregnancy at home

  • At-home fecal testing

The "fertility window"

There's a period of time commonly referred to as a "fertility window." Pretty much what it sounds like, the window of time when you can expect a girl to be fertile.

The window starts with ovulation (or LH if your vet prefers LH testing) and ends with going out of cytological estrus.

Best practice is to use cytology to let you know when to start progesterone testing.

The progesterone then tells you when she ovulates.

Cytology tells you when she's out of "cytological estrus," which means her cervix has closed for business along with your fertility window.

I start cytology about 5 days into a cycle, assuming I don't have a girl with a known short cycle.

Ovulation can happen within a few days of the cycle starting or as late as 3 weeks in.

This is why cytology/progesterone is so important. Breeding based on day of heat can very easily miss the fertile window.

Breeding on certain days or using first tie for whelping estimate

Back in the day, progesterone testing was not available, so we typically bred on days 11 and 13, since those are average days of ovulation.

But that method or predicting whelping date based on day of first tie can be off by a week or 10 days.

Now that we have progesterone testing available there's no reason not to know the actual day.

Progesterone, ovulation, and whelping due dates

Even more important about knowing the day of ovulation (or LH) is that ovulation is by far the most accurate predictor of whelping due date than any other method.

Prediction of due date is accurate within 1-2 days plus or minus the due date based on ovulation.

It can be as much as 10 days off plus or minus without it.

Not only is this a matter of convenience, it's a matter of safety for your dam and puppies. If you know when she's due, you can plan to be there. Just as importantly, you can know when she's overdue, which can be deadly for both her and the puppies if not addressed.

Need more help?

You are not alone! Please reach out to us and we will be happy to work with you. Email Ji at


Please comment below if you like this article, have anything to add, or disagree with something in it. We want to hear from you!

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