When a pregnant patient walks into our clinic, it isn’t enough for us to know her due date. It is also critically important for us to know how that date was determined.
Canine gestation length is 63 days from the day of ovulation. However, because we can’t SEE when ovulation happens with our eyes, many people misguidedly substitute the date she was bred for ovulation date, assuming that her breeding date and ovulation date must be “close enough” that it won’t matter.
Unfortunately, biology isn’t that simple. Canine semen can survive in the female’s reproductive tract for up to 9 days, which means that the sperm could be hanging out for a long time before it finds an egg to fertilize. Furthermore, while some females will reliably stand for breeding only when they’re fertile, many others will stand to be bred for days before or after their peak fertility, and some females will not stand to be bred AT ALL – even when their eggs are ready for fertilization!
Because of these factors, when determining due date based on breeding dates, the due date can vary anywhere from 59 to 72 days post breeding. This is a huge window and is typically not very helpful!
Substituting breeding date for ovulation can be a dangerous assumption. Consider, for example, if she was actually bred four days after ovulation. The due date would be incorrectly estimated four days later than her actual due date. She could be past her due date, the puppies could be dying, and the breeder may not suspect anything because they think she isn’t “due” yet.
There are two methods I recommend for identifying due date: serial progesterone measurements and ultrasound. There are also other methods of determining gestation length, including LH testing and identifying the first day of diestrus via vaginal cytology. I personally don’t prefer these methods and so they are not addressed here.
The most specific way of identifying due date is to identify the date of ovulation based on serial progesterone measurements. Progesterone starts at baseline before the female is in heat, then starts to rise. The LH surge happens when progesterone is between 2-3 ng/mL, and ovulation follows approximately 2 days later when progesterone is between 5-10 ng/mL. Gestation length is 63 +/- 1 days from ovulation. This gives us a much tighter window to observe the female and ensure that whelping proceeds in a timely manner.
Ultrasound can also be used to determine due date. Based on the size of the embryonic vesicle and the size of the breed, due date can be calculated mathematically. Although this is not as specific as progesterone, it can be a useful technique in cases when progesterone measurements were not taken to identify timing of ovulation, and it is more specific than relying on breeding dates alone.
In summary, canine gestation length is 63 days from ovulation, which can be determined by measuring progesterone before breeding. Breeding dates provide only a broad estimate of due date, as perceived gestation length from date of breeding can be 59-72 days. If progesterone is not measured prior to breeding, ultrasound can be used to estimate due date.
Yours in healthy, responsibly-bred puppies,