The Estrous Cycle
The estrous cycle is divided into three parts: proestrus, estrus and diestrus.
Proestrus starts when the bitch shows her first signs of heat: swelling of the vulva, a blood-tinged vaginal discharge, and attractiveness to male dogs. During this time her estrogen level is rising, and her body is preparing for ovulation. This period lasts 9 days on average, with a range of 2 – 22 days.
Estrus starts when the bitch solicits and permits mating. You may see her flagging (holding her tail to the side) or showing lordosis (arching her back to raise her hind end and vulva up for the male). During this time her estrogen is dropping, her progesterone is rising, and her LH (luteinizing hormone) peaks and falls. This period lasts 9 days on average, with a range of 4 – 21 days.
Diestrus starts when the bitch aggressively prevents mating. During this time her progesterone level is slowly falling. This period lasts 120 days on average in the non-pregnant bitch.
Anestrus is the inactive period until the start of the next estrus.
Natural mating: If you plan to breed by natural mating, you can either put the dog and the bitch together for the entire estrous period, or allow them to mate every other day as long as the bitch allows.
Preferably there should be at least three breedings in the first 6 days after ovulation. In many dogs, this is a successful way to breed. However, closely monitoring the bitch’s hormonal profile is required if you do not have ready access to the dog, do not want to risk passing an infectious disease, the dogs do not mate willingly, the bitch has missed before (been bred but not become pregnant), or you expect that delivery will need to be by caesarian section.
Breeding by following hormones: following the bitch’s hormonal changes allows you to know precisely when she ovulates, and therefore when her best breeding times are, and when she is likely to deliver.
This allows you to breed using fresh chilled semen, frozen semen, or by giving the pair limited access to one-another. It also allows for accurate calculation of the due date, which is especially important if a caesarian section is expected.
1. Measure a baseline progesterone at the first noticeable signs of heat. It usually measures < 1.0 ng/ml at this time.
2. About 4 days later, start measuring progesterone every other day. We save serum each time so that LH can be checked later, if needed. This frequency is necessary to ensure that ovulation is not missed.
3. When progesterone is > 2.0 ng/ml (or twice the baseline level), we measure LH. This rise in progesterone is the best indicator that the LH surge has taken place. Since the LH surge lasts only 12 – 24 hours, it can easily be missed if that was the only level you were following. By following the progesterone, you can narrow down the time of the LH surge very accurately.
4. The LH surge initiates ovulation.
5. Eggs are released (ovulated) 44 hours (2 days) after the LH surge, on average. The eggs are viable for about 3 – 4 days after this (5 – 6 days after the LH surge).
6. Breeding the bitch on days 3 and 5 (or 4 and 6) after the LH surge ensures the maximum conception rate and largest litter sizes. If only one breeding is possible, do it on day 5 or 6 after the LH surge. See our “Canine Breeding Options” handout for more information.
7. Gestation lasts 65 +/- 1 day from the LH surge (63 +/- 1 day from ovulation). If the hormonal information is not available, gestation lasts 63 +/- 8 days from mating.
During the first 20 days, the embryos are free-floating in the uterus. They implant around day 20, and from then until day 40 is when the majority of development takes place. After day 40 the skeletons are mineralizing, and the puppies are steadily growing.